rusty_pool/

lib.rs

#[cfg(feature = "async")]
use futures::{
    future::BoxFuture,
    task::{waker_ref, ArcWake},
};
use futures_channel::oneshot;
use futures_executor::block_on;
use std::future::Future;
use std::option::Option;
use std::sync::{
    atomic::{AtomicUsize, Ordering},
    Arc, Condvar, Mutex,
};
#[cfg(feature = "async")]
use std::task::Context;
use std::thread;
use std::time::Duration;

const BITS: usize = std::mem::size_of::<usize>() * 8;
/// The absolute maximum number of workers. This corresponds to the maximum value that can be stored within half the bits of usize,
/// as two counters (total workers and idle workers) are stored in one AtomicUsize.
pub const MAX_SIZE: usize = (1 << (BITS / 2)) - 1;

type Job = Box<dyn FnOnce() + Send + 'static>;

/// Trait to implement for all items that may be executed by the `ThreadPool`.
pub trait Task<R: Send>: Send {
    /// Execute this task and return its result.
    fn run(self) -> R;

    /// Transform this `Task` into a heap allocated `FnOnce` if possible.
    ///
    /// Used by [`ThreadPool::execute`](struct.ThreadPool.html#method.execute) to turn this `Task` into a `Job`
    /// directly without having to create an additional `Job` that calls this `Task`.
    fn into_fn(self) -> Option<Box<dyn FnOnce() -> R + Send + 'static>>;

    /// Return `true` if calling [`Task::into_fn`] on this `Task` returns `Some`.
    fn is_fn(&self) -> bool;
}

/// Implement the `Task` trait for any FnOnce closure that returns a thread-safe result.
impl<R, F> Task<R> for F
where
    R: Send,
    F: FnOnce() -> R + Send + 'static,
{
    fn run(self) -> R {
        self()
    }

    fn into_fn(self) -> Option<Box<dyn FnOnce() -> R + Send + 'static>> {
        Some(Box::new(self))
    }

    fn is_fn(&self) -> bool {
        true
    }
}

/// Handle returned by [`ThreadPool::evaluate`](struct.ThreadPool.html#method.evaluate) and [`ThreadPool::complete`](struct.ThreadPool.html#method.complete)
/// that allows to block the current thread and wait for the result of a submitted task. The returned `JoinHandle` may also be sent to the [`ThreadPool`](struct.ThreadPool.html)
/// to create a task that blocks a worker thread until the task is completed and then does something with the result. This handle communicates with the worker thread
/// using a oneshot channel blocking the thread when [`try_await_complete()`](struct.JoinHandle.html#method.try_await_complete) is called until a message, i.e. the result of the
/// task, is received.
pub struct JoinHandle<T: Send> {
    pub receiver: oneshot::Receiver<T>,
}

impl<T: Send> JoinHandle<T> {
    /// Block the current thread until the result of the task is received.
    ///
    /// # Errors
    ///
    /// This function might return a `oneshot::Canceled` if the channel was broken
    /// before the result was received. This is generally the case if execution of
    /// the task panicked.
    pub fn try_await_complete(self) -> Result<T, oneshot::Canceled> {
        block_on(self.receiver)
    }

    /// Block the current thread until the result of the task is received.
    ///
    /// # Panics
    ///
    /// This function might panic if [`try_await_complete()`](struct.JoinHandle.html#method.try_await_complete) returns `oneshot::Canceled`.
    /// This is generally the case if execution of the task panicked and the sender was dropped before sending a result to the receiver.
    pub fn await_complete(self) -> T {
        self.try_await_complete()
            .expect("could not receive message because channel was cancelled")
    }
}

#[cfg(feature = "async")]
struct AsyncTask {
    future: Mutex<Option<BoxFuture<'static, ()>>>,
    pool: ThreadPool,
}

/// Implement `ArcWake` for `AsyncTask` by re-submitting the `AsyncTask` i.e. the `Future` to the pool.
#[cfg(feature = "async")]
impl ArcWake for AsyncTask {
    fn wake_by_ref(arc_self: &Arc<Self>) {
        let cloned_task = arc_self.clone();
        arc_self
            .pool
            .try_execute(cloned_task)
            .expect("failed to wake future because message could not be sent to pool");
    }
}

/// Implement the `Task` trait for `AsyncTask` in order to make it executable for the pool by
/// creating a waker and polling the future.
#[cfg(feature = "async")]
impl Task<()> for Arc<AsyncTask> {
    fn run(self) {
        let mut future_slot = self.future.lock().expect("failed to acquire mutex");
        if let Some(mut future) = future_slot.take() {
            let waker = waker_ref(&self);
            let context = &mut Context::from_waker(&*waker);
            if future.as_mut().poll(context).is_pending() {
                *future_slot = Some(future);
            }
        }
    }

    fn into_fn(self) -> Option<Box<dyn FnOnce() + Send + 'static>> {
        None
    }

    fn is_fn(&self) -> bool {
        false
    }
}

// assert that Send is implemented
trait ThreadSafe: Send {}

impl<R: Send> ThreadSafe for dyn Task<R> {}

impl<R: Send> ThreadSafe for JoinHandle<R> {}

impl ThreadSafe for ThreadPool {}

/// Self growing / shrinking `ThreadPool` implementation based on crossbeam's
/// multi-producer multi-consumer channels that enables awaiting the result of a
/// task and offers async support.
///
/// This `ThreadPool` has two different pool sizes; a core pool size filled with
/// threads that live for as long as the channel and a max pool size which describes
/// the maximum amount of worker threads that may live at the same time.
/// Those additional non-core threads have a specific keep_alive time described when
/// creating the `ThreadPool` that defines how long such threads may be idle for
/// without receiving any work before giving up and terminating their work loop.
///
/// This `ThreadPool` does not spawn any threads until a task is submitted to it.
/// Then it will create a new thread for each task until the core pool size is full.
/// After that a new thread will only be created upon an `execute()` call if the
/// current pool is lower than the max pool size and there are no idle threads.
///
/// Functions like `evaluate()` and `complete()` return a `JoinHandle` that may be used
/// to await the result of a submitted task or future. JoinHandles may be sent to the
/// thread pool to create a task that blocks a worker thread until it receives the
/// result of the other task and then operates on the result. If the task panics the
/// `JoinHandle` receives a cancellation error. This is implemented using a futures
/// oneshot channel to communicate with the worker thread.
///
/// This `ThreadPool` may be used as a futures executor if the "async" feature is enabled,
/// which is the case by default. The "async" feature includes the `spawn()` and
/// `try_spawn()` functions which create a task that polls the future one by one and
/// creates a waker that re-submits the future to the pool when it can make progress.
/// Without the "async" feature, futures can simply be executed to completion using
/// the `complete` function, which simply blocks a worker thread until the future has
/// been polled to completion.
///
/// The "async" feature can be disabled if not need by adding the following to your
/// Cargo dependency:
/// ```toml
/// [dependencies.rusty_pool]
/// default-features = false
/// version = "*"
/// ```
///
/// When creating a new worker this `ThreadPool` tries to increment the worker count
/// using a compare-and-swap mechanism, if the increment fails because the total worker
/// count has been incremented to the specified limit (the core_size when trying to
/// create a core thread, else the max_size) by another thread, the pool tries to create
/// a non-core worker instead (if previously trying to create a core worker and no idle
/// worker exists) or sends the task to the channel instead. Panicking workers are always
/// cloned and replaced.
///
/// Locks are only used for the join functions to lock the `Condvar`, apart from that
/// this `ThreadPool` implementation fully relies on crossbeam and atomic operations.
/// This `ThreadPool` decides whether it is currently idle (and should fast-return
/// join attempts) by comparing the total worker count to the idle worker count, which
/// are two values stored in one `AtomicUsize` (both half the size of usize) making sure
/// that if both are updated they may be updated in a single atomic operation.
///
/// The thread pool and its crossbeam channel can be destroyed by using the shutdown
/// function, however that does not stop tasks that are already running but will
/// terminate the thread the next time it will try to fetch work from the channel.
/// The channel is only destroyed once all clones of the `ThreadPool` have been
/// shut down / dropped.
///
/// # Usage
/// Create a new `ThreadPool`:
/// ```rust
/// use rusty_pool::Builder;
/// use rusty_pool::ThreadPool;
/// // Create default `ThreadPool` configuration with the number of CPUs as core pool size
/// let pool = ThreadPool::default();
/// // Create a `ThreadPool` with default naming:
/// use std::time::Duration;
/// let pool2 = ThreadPool::new(5, 50, Duration::from_secs(60));
/// // Create a `ThreadPool` with a custom name:
/// let pool3 = ThreadPool::new_named(String::from("my_pool"), 5, 50, Duration::from_secs(60));
/// // using the Builder struct:
/// let pool4 = Builder::new().core_size(5).max_size(50).build();
/// ```
///
/// Submit a closure for execution in the `ThreadPool`:
/// ```rust
/// use rusty_pool::ThreadPool;
/// use std::thread;
/// use std::time::Duration;
/// let pool = ThreadPool::default();
/// pool.execute(|| {
///     thread::sleep(Duration::from_secs(5));
///     print!("hello");
/// });
/// ```
///
/// Submit a task and await the result:
/// ```rust
/// use rusty_pool::ThreadPool;
/// use std::thread;
/// use std::time::Duration;
/// let pool = ThreadPool::default();
/// let handle = pool.evaluate(|| {
///     thread::sleep(Duration::from_secs(5));
///     return 4;
/// });
/// let result = handle.await_complete();
/// assert_eq!(result, 4);
/// ```
///
/// Spawn futures using the `ThreadPool`:
/// ```rust
/// async fn some_async_fn(x: i32, y: i32) -> i32 {
///     x + y
/// }
///
/// async fn other_async_fn(x: i32, y: i32) -> i32 {
///     x - y
/// }
///
/// use rusty_pool::ThreadPool;
/// let pool = ThreadPool::default();
///
/// // simply complete future by blocking a worker until the future has been completed
/// let handle = pool.complete(async {
///     let a = some_async_fn(4, 6).await; // 10
///     let b = some_async_fn(a, 3).await; // 13
///     let c = other_async_fn(b, a).await; // 3
///     some_async_fn(c, 5).await // 8
/// });
/// assert_eq!(handle.await_complete(), 8);
///
/// use std::sync::{Arc, atomic::{AtomicI32, Ordering}};
///
/// // spawn future and create waker that automatically re-submits itself to the threadpool if ready to make progress, this requires the "async" feature which is enabled by default
/// let count = Arc::new(AtomicI32::new(0));
/// let clone = count.clone();
/// pool.spawn(async move {
///     let a = some_async_fn(3, 6).await; // 9
///     let b = other_async_fn(a, 4).await; // 5
///     let c = some_async_fn(b, 7).await; // 12
///     clone.fetch_add(c, Ordering::Relaxed);
/// });
/// pool.join();
/// assert_eq!(count.load(Ordering::Relaxed), 12);
/// ```
///
/// Join and shut down the `ThreadPool`:
/// ```rust
/// use std::thread;
/// use std::time::Duration;
/// use rusty_pool::ThreadPool;
/// use std::sync::{Arc, atomic::{AtomicI32, Ordering}};
///
/// let pool = ThreadPool::default();
/// for _ in 0..10 {
///     pool.execute(|| { thread::sleep(Duration::from_secs(10)) })
/// }
/// // wait for all threads to become idle, i.e. all tasks to be completed including tasks added by other threads after join() is called by this thread or for the timeout to be reached
/// pool.join_timeout(Duration::from_secs(5));
///
/// let count = Arc::new(AtomicI32::new(0));
/// for _ in 0..15 {
///     let clone = count.clone();
///     pool.execute(move || {
///         thread::sleep(Duration::from_secs(5));
///         clone.fetch_add(1, Ordering::Relaxed);
///     });
/// }
///
/// // shut down and drop the only instance of this `ThreadPool` (no clones) causing the channel to be broken leading all workers to exit after completing their current work
/// // and wait for all workers to become idle, i.e. finish their work.
/// pool.shutdown_join();
/// assert_eq!(count.load(Ordering::Relaxed), 15);
/// ```
#[derive(Clone)]
pub struct ThreadPool {
    core_size: usize,
    max_size: usize,
    keep_alive: Duration,
    channel_data: Arc<ChannelData>,
    worker_data: Arc<WorkerData>,
}

impl ThreadPool {
    /// Construct a new `ThreadPool` with the specified core pool size, max pool size
    /// and keep_alive time for non-core threads. This function does not spawn any
    /// threads. This `ThreadPool` will receive a default name in the following format:
    /// "rusty_pool_" + pool number.
    ///
    /// `core_size` specifies the amount of threads to keep alive for as long as
    /// the `ThreadPool` exists and its channel remains connected.
    ///
    /// `max_size` specifies the maximum number of worker threads that may exist
    /// at the same time.
    ///
    /// `keep_alive` specifies the duration for which to keep non-core pool
    /// worker threads alive while they do not receive any work.
    ///
    /// # Panics
    ///
    /// This function will panic if max_size is 0, lower than core_size or exceeds half
    /// the size of usize. This restriction exists because two counters (total workers and
    /// idle counters) are stored within one AtomicUsize.
    pub fn new(core_size: usize, max_size: usize, keep_alive: Duration) -> Self {
        static POOL_COUNTER: AtomicUsize = AtomicUsize::new(1);
        let name = format!(
            "rusty_pool_{}",
            POOL_COUNTER.fetch_add(1, Ordering::Relaxed)
        );
        ThreadPool::new_named(name, core_size, max_size, keep_alive)
    }

    /// Construct a new `ThreadPool` with the specified name, core pool size, max pool size
    /// and keep_alive time for non-core threads. This function does not spawn any
    /// threads.
    ///
    /// `name` the name of the `ThreadPool` that will be used as prefix for each
    /// thread.
    ///
    /// `core_size` specifies the amount of threads to keep alive for as long as
    /// the `ThreadPool` exists and its channel remains connected.
    ///
    /// `max_size` specifies the maximum number of worker threads that may exist
    /// at the same time.
    ///
    /// `keep_alive` specifies the duration for which to keep non-core pool
    /// worker threads alive while they do not receive any work.
    ///
    /// # Panics
    ///
    /// This function will panic if max_size is 0, lower than core_size or exceeds half
    /// the size of usize. This restriction exists because two counters (total workers and
    /// idle counters) are stored within one AtomicUsize.
    pub fn new_named(
        name: String,
        core_size: usize,
        max_size: usize,
        keep_alive: Duration,
    ) -> Self {
        let (sender, receiver) = crossbeam_channel::unbounded();

        if max_size == 0 || max_size < core_size {
            panic!("max_size must be greater than 0 and greater or equal to the core pool size");
        } else if max_size > MAX_SIZE {
            panic!(
                "max_size may not exceed {}, the maximum value that can be stored within half the bits of usize ({} -> {} bits in this case)",
                MAX_SIZE,
                BITS,
                BITS / 2
            );
        }

        let worker_data = WorkerData {
            pool_name: name,
            worker_count_data: WorkerCountData::default(),
            worker_number: AtomicUsize::new(1),
            join_notify_condvar: Condvar::new(),
            join_notify_mutex: Mutex::new(()),
            join_generation: AtomicUsize::new(0),
        };

        let channel_data = ChannelData { sender, receiver };

        Self {
            core_size,
            max_size,
            keep_alive,
            channel_data: Arc::new(channel_data),
            worker_data: Arc::new(worker_data),
        }
    }

    /// Get the number of live workers, includes all workers waiting for work or executing tasks.
    ///
    /// This counter is incremented when creating a new worker. The value is increment just before
    /// the worker starts executing its initial task. Incrementing the worker total might fail
    /// if the total has already reached the specified limit (either core_size or max_size) after
    /// being incremented by another thread, as of rusty_pool 0.5.0 failed attempts to create a worker
    /// no longer skews the worker total as failed attempts to increment the worker total does not
    /// increment the value at all.
    /// This counter is decremented when a worker reaches the end of its working loop, which for non-core
    /// threads might happen if it does not receive any work during its keep alive time,
    /// for core threads this only happens once the channel is disconnected.
    pub fn get_current_worker_count(&self) -> usize {
        self.worker_data.worker_count_data.get_total_worker_count()
    }

    /// Get the number of workers currently waiting for work. Those threads are currently
    /// polling from the crossbeam receiver. Core threads wait indefinitely and might remain
    /// in this state until the `ThreadPool` is dropped. The remaining threads give up after
    /// waiting for the specified keep_alive time.
    pub fn get_idle_worker_count(&self) -> usize {
        self.worker_data.worker_count_data.get_idle_worker_count()
    }

    /// Send a new task to the worker threads. This function is responsible for sending the message through the
    /// channel and creating new workers if needed. If the current worker count is lower than the core pool size
    /// this function will always create a new worker. If the current worker count is equal to or greater than
    /// the core pool size this function only creates a new worker if the worker count is below the max pool size
    /// and there are no idle threads.
    ///
    /// When attempting to increment the total worker count before creating a worker fails due to the
    /// counter reaching the provided limit (core_size when attempting to create core thread, else
    /// max_size) after being incremented by another thread, the pool tries to create
    /// a non-core worker instead (if previously trying to create a core worker and no idle
    /// worker exists) or sends the task to the channel instead. If incrementing the counter succeeded,
    /// either because the current value of the counter matched the expected value or because the
    /// last observed value was still below the limit, the worker starts with the provided task as
    /// initial task and spawns its thread.
    ///
    /// # Panics
    ///
    /// This function might panic if `try_execute` returns an error when the crossbeam channel has been
    /// closed unexpectedly.
    /// This should never occur under normal circumstances using safe code, as shutting down the `ThreadPool`
    /// consumes ownership and the crossbeam channel is never dropped unless dropping the `ThreadPool`.
    pub fn execute<T: Task<()> + 'static>(&self, task: T) {
        if self.try_execute(task).is_err() {
            panic!("the channel of the thread pool has been closed");
        }
    }

    /// Send a new task to the worker threads. This function is responsible for sending the message through the
    /// channel and creating new workers if needed. If the current worker count is lower than the core pool size
    /// this function will always create a new worker. If the current worker count is equal to or greater than
    /// the core pool size this function only creates a new worker if the worker count is below the max pool size
    /// and there are no idle threads.
    ///
    /// When attempting to increment the total worker count before creating a worker fails due to the
    /// counter reaching the provided limit (core_size when attempting to create core thread, else
    /// max_size) after being incremented by another thread, the pool tries to create
    /// a non-core worker instead (if previously trying to create a core worker and no idle
    /// worker exists) or sends the task to the channel instead. If incrementing the counter succeeded,
    /// either because the current value of the counter matched the expected value or because the
    /// last observed value was still below the limit, the worker starts with the provided task as
    /// initial task and spawns its thread.
    ///
    /// # Errors
    ///
    /// This function might return `crossbeam_channel::SendError` if the sender was dropped unexpectedly.
    pub fn try_execute<T: Task<()> + 'static>(
        &self,
        task: T,
    ) -> Result<(), crossbeam_channel::SendError<Job>> {
        if task.is_fn() {
            self.try_execute_task(
                task.into_fn()
                    .expect("Task::into_fn returned None despite is_fn returning true"),
            )
        } else {
            self.try_execute_task(Box::new(move || {
                task.run();
            }))
        }
    }

    /// Send a new task to the worker threads and return a [`JoinHandle`](struct.JoinHandle.html) that may be used to await
    /// the result. This function is responsible for sending the message through the channel and creating new
    /// workers if needed. If the current worker count is lower than the core pool size this function will always
    /// create a new worker. If the current worker count is equal to or greater than the core pool size this
    /// function only creates a new worker if the worker count is below the max pool size and there are no idle
    /// threads.
    ///
    /// When attempting to increment the total worker count before creating a worker fails due to the
    /// counter reaching the provided limit (core_size when attempting to create core thread, else
    /// max_size) after being incremented by another thread, the pool tries to create
    /// a non-core worker instead (if previously trying to create a core worker and no idle
    /// worker exists) or sends the task to the channel instead. If incrementing the counter succeeded,
    /// either because the current value of the counter matched the expected value or because the
    /// last observed value was still below the limit, the worker starts with the provided task as
    /// initial task and spawns its thread.
    ///
    /// # Panics
    ///
    /// This function might panic if `try_execute` returns an error when the crossbeam channel has been
    /// closed unexpectedly.
    /// This should never occur under normal circumstances using safe code, as shutting down the `ThreadPool`
    /// consumes ownership and the crossbeam channel is never dropped unless dropping the `ThreadPool`.
    pub fn evaluate<R: Send + 'static, T: Task<R> + 'static>(&self, task: T) -> JoinHandle<R> {
        match self.try_evaluate(task) {
            Ok(handle) => handle,
            Err(e) => panic!("the channel of the thread pool has been closed: {:?}", e),
        }
    }

    /// Send a new task to the worker threads and return a [`JoinHandle`](struct.JoinHandle.html) that may be used to await
    /// the result. This function is responsible for sending the message through the channel and creating new
    /// workers if needed. If the current worker count is lower than the core pool size this function will always
    /// create a new worker. If the current worker count is equal to or greater than the core pool size this
    /// function only creates a new worker if the worker count is below the max pool size and there are no idle
    /// threads.
    ///
    /// When attempting to increment the total worker count before creating a worker fails due to the
    /// counter reaching the provided limit (core_size when attempting to create core thread, else
    /// max_size) after being incremented by another thread, the pool tries to create
    /// a non-core worker instead (if previously trying to create a core worker and no idle
    /// worker exists) or sends the task to the channel instead. If incrementing the counter succeeded,
    /// either because the current value of the counter matched the expected value or because the
    /// last observed value was still below the limit, the worker starts with the provided task as
    /// initial task and spawns its thread.
    ///
    /// # Errors
    ///
    /// This function might return `crossbeam_channel::SendError` if the sender was dropped unexpectedly.
    pub fn try_evaluate<R: Send + 'static, T: Task<R> + 'static>(
        &self,
        task: T,
    ) -> Result<JoinHandle<R>, crossbeam_channel::SendError<Job>> {
        let (sender, receiver) = oneshot::channel::<R>();
        let join_handle = JoinHandle { receiver };
        let job = || {
            let result = task.run();
            // if the receiver was dropped that means the caller was not interested in the result
            let _ignored_result = sender.send(result);
        };

        let execute_attempt = self.try_execute_task(Box::new(job));
        execute_attempt.map(|_| join_handle)
    }

    /// Send a task to the `ThreadPool` that completes the given `Future` and return a [`JoinHandle`](struct.JoinHandle.html)
    /// that may be used to await the result. This function simply calls [`evaluate()`](struct.ThreadPool.html#method.evaluate)
    /// with a closure that calls `block_on` with the provided future.
    ///
    /// # Panic
    ///
    /// This function panics if the task fails to be sent to the `ThreadPool` due to the channel being broken.
    pub fn complete<R: Send + 'static>(
        &self,
        future: impl Future<Output = R> + 'static + Send,
    ) -> JoinHandle<R> {
        self.evaluate(|| block_on(future))
    }

    /// Send a task to the `ThreadPool` that completes the given `Future` and return a [`JoinHandle`](struct.JoinHandle.html)
    /// that may be used to await the result. This function simply calls [`try_evaluate()`](struct.ThreadPool.html#method.try_evaluate)
    /// with a closure that calls `block_on` with the provided future.
    ///
    /// # Errors
    ///
    /// This function returns `crossbeam_channel::SendError` if the task fails to be sent to the `ThreadPool` due to the channel being broken.
    pub fn try_complete<R: Send + 'static>(
        &self,
        future: impl Future<Output = R> + 'static + Send,
    ) -> Result<JoinHandle<R>, crossbeam_channel::SendError<Job>> {
        self.try_evaluate(|| block_on(future))
    }

    /// Submit a `Future` to be polled by this `ThreadPool`. Unlike [`complete()`](struct.ThreadPool.html#method.complete) this does not
    /// block a worker until the `Future` has been completed but polls the `Future` once at a time and creates a `Waker`
    /// that re-submits the Future to this pool when awakened. Since `Arc<AsyncTask>` implements the [`Task`](trait.Task.html) trait this
    /// function simply constructs the `AsyncTask` and calls [`execute()`](struct.ThreadPool.html#method.execute).
    ///
    /// # Panic
    ///
    /// This function panics if the task fails to be sent to the `ThreadPool` due to the channel being broken.
    #[cfg(feature = "async")]
    pub fn spawn(&self, future: impl Future<Output = ()> + 'static + Send) {
        let future_task = Arc::new(AsyncTask {
            future: Mutex::new(Some(Box::pin(future))),
            pool: self.clone(),
        });

        self.execute(future_task)
    }

    /// Submit a `Future` to be polled by this `ThreadPool`. Unlike [`try_complete()`](struct.ThreadPool.html#method.try_complete) this does not
    /// block a worker until the `Future` has been completed but polls the `Future` once at a time and creates a `Waker`
    /// that re-submits the Future to this pool when awakened. Since `Arc<AsyncTask>` implements the [`Task`](trait.Task.html) trait this
    /// function simply constructs the `AsyncTask` and calls [`try_execute()`](struct.ThreadPool.html#method.try_execute).
    ///
    /// # Errors
    ///
    /// This function returns `crossbeam_channel::SendError` if the task fails to be sent to the `ThreadPool` due to the channel being broken.
    #[cfg(feature = "async")]
    pub fn try_spawn(
        &self,
        future: impl Future<Output = ()> + 'static + Send,
    ) -> Result<(), crossbeam_channel::SendError<Job>> {
        let future_task = Arc::new(AsyncTask {
            future: Mutex::new(Some(Box::pin(future))),
            pool: self.clone(),
        });

        self.try_execute(future_task)
    }

    /// Create a top-level `Future` that awaits the provided `Future` and then sends the result to the
    /// returned [`JoinHandle`](struct.JoinHandle.html). Unlike [`complete()`](struct.ThreadPool.html#method.complete) this does not
    /// block a worker until the `Future` has been completed but polls the `Future` once at a time and creates a `Waker`
    /// that re-submits the Future to this pool when awakened. Since `Arc<AsyncTask>` implements the [`Task`](trait.Task.html) trait this
    /// function simply constructs the `AsyncTask` and calls [`execute()`](struct.ThreadPool.html#method.execute).
    ///
    /// This enables awaiting the final result outside of an async context like [`complete()`](struct.ThreadPool.html#method.complete) while still
    /// polling the future lazily instead of eagerly blocking the worker until the future is done.
    ///
    /// # Panic
    ///
    /// This function panics if the task fails to be sent to the `ThreadPool` due to the channel being broken.
    #[cfg(feature = "async")]
    pub fn spawn_await<R: Send + 'static>(
        &self,
        future: impl Future<Output = R> + 'static + Send,
    ) -> JoinHandle<R> {
        match self.try_spawn_await(future) {
            Ok(handle) => handle,
            Err(e) => panic!("the channel of the thread pool has been closed: {:?}", e),
        }
    }

    /// Create a top-level `Future` that awaits the provided `Future` and then sends the result to the
    /// returned [`JoinHandle`](struct.JoinHandle.html). Unlike [`try_complete()`](struct.ThreadPool.html#method.try_complete) this does not
    /// block a worker until the `Future` has been completed but polls the `Future` once at a time and creates a `Waker`
    /// that re-submits the Future to this pool when awakened. Since `Arc<AsyncTask>` implements the [`Task`](trait.Task.html) trait this
    /// function simply constructs the `AsyncTask` and calls [`try_execute()`](struct.ThreadPool.html#method.try_execute).
    ///
    /// This enables awaiting the final result outside of an async context like [`complete()`](struct.ThreadPool.html#method.complete) while still
    /// polling the future lazily instead of eagerly blocking the worker until the future is done.
    ///
    /// # Errors
    ///
    /// This function returns `crossbeam_channel::SendError` if the task fails to be sent to the `ThreadPool` due to the channel being broken.
    #[cfg(feature = "async")]
    pub fn try_spawn_await<R: Send + 'static>(
        &self,
        future: impl Future<Output = R> + 'static + Send,
    ) -> Result<JoinHandle<R>, crossbeam_channel::SendError<Job>> {
        let (sender, receiver) = oneshot::channel::<R>();
        let join_handle = JoinHandle { receiver };

        self.try_spawn(async {
            let result = future.await;
            // if the receiver was dropped that means the caller was not interested in the result
            let _ignored_result = sender.send(result);
        })
        .map(|_| join_handle)
    }

    #[inline]
    fn try_execute_task(&self, task: Job) -> Result<(), crossbeam_channel::SendError<Job>> {
        // create a new worker either if the current worker count is lower than the core pool size
        // or if there are no idle threads and the current worker count is lower than the max pool size
        let worker_count_data = &self.worker_data.worker_count_data;
        let mut worker_count_val = worker_count_data.worker_count.load(Ordering::Relaxed);
        let (mut curr_worker_count, idle_worker_count) = WorkerCountData::split(worker_count_val);
        let mut curr_idle_count = idle_worker_count;

        // always create a new worker if current pool size is below core size
        if curr_worker_count < self.core_size {
            let witnessed =
                worker_count_data.try_increment_worker_total(worker_count_val, self.core_size);

            // the witnessed value matched the expected value, meaning the initial exchange succeeded, or the final witnessed
            // value is still below the coreSize, meaning the increment eventually succeeded
            if witnessed == worker_count_val
                || WorkerCountData::get_total_count(witnessed) < self.core_size
            {
                let worker = Worker::new(
                    self.channel_data.receiver.clone(),
                    Arc::clone(&self.worker_data),
                    None,
                );

                worker.start(Some(task));
                return Ok(());
            }

            curr_worker_count = WorkerCountData::get_total_count(witnessed);
            curr_idle_count = WorkerCountData::get_idle_count(witnessed);
            worker_count_val = witnessed;
        }

        // create a new worker if the current worker count is below the maxSize and the pool has been observed to be busy
        // (no idle workers) during the invocation of this function
        if curr_worker_count < self.max_size && (idle_worker_count == 0 || curr_idle_count == 0) {
            let witnessed =
                worker_count_data.try_increment_worker_total(worker_count_val, self.max_size);

            if witnessed == worker_count_val
                || WorkerCountData::get_total_count(witnessed) < self.max_size
            {
                let worker = Worker::new(
                    self.channel_data.receiver.clone(),
                    Arc::clone(&self.worker_data),
                    Some(self.keep_alive),
                );

                worker.start(Some(task));
                return Ok(());
            }
        }

        self.send_task_to_channel(task)
    }

    /// Blocks the current thread until there aren't any non-idle threads anymore.
    /// This includes work started after calling this function.
    /// This function blocks until the next time this `ThreadPool` completes all of its work,
    /// except if all threads are idle and the channel is empty at the time of calling this
    /// function, in which case it will fast-return.
    ///
    /// This utilizes a `Condvar` that is notified by workers when they complete a job and notice
    /// that the channel is currently empty and it was the last thread to finish the current
    /// generation of work (i.e. when incrementing the idle worker counter brings the value
    /// up to the total worker counter, meaning it's the last thread to become idle).
    pub fn join(&self) {
        self.inner_join(None);
    }

    /// Blocks the current thread until there aren't any non-idle threads anymore or until the
    /// specified time_out Duration passes, whichever happens first.
    /// This includes work started after calling this function.
    /// This function blocks until the next time this `ThreadPool` completes all of its work,
    /// (or until the time_out is reached) except if all threads are idle and the channel is
    /// empty at the time of calling this function, in which case it will fast-return.
    ///
    /// This utilizes a `Condvar` that is notified by workers when they complete a job and notice
    /// that the channel is currently empty and it was the last thread to finish the current
    /// generation of work (i.e. when incrementing the idle worker counter brings the value
    /// up to the total worker counter, meaning it's the last thread to become idle).
    pub fn join_timeout(&self, time_out: Duration) {
        self.inner_join(Some(time_out));
    }

    /// Destroy this `ThreadPool` by claiming ownership and dropping the value,
    /// causing the `Sender` to drop thus disconnecting the channel.
    /// Threads in this pool that are currently executing a task will finish what
    /// they're doing until they check the channel, discovering that it has been
    /// disconnected from the sender and thus terminate their work loop.
    ///
    /// If other clones of this `ThreadPool` exist the sender will remain intact
    /// and tasks submitted to those clones will succeed, this includes pending
    /// `AsyncTask` instances as they hold an owned clone of the `ThreadPool`
    /// to re-submit awakened futures.
    pub fn shutdown(self) {
        drop(self);
    }

    /// Destroy this `ThreadPool` by claiming ownership and dropping the value,
    /// causing the `Sender` to drop thus disconnecting the channel.
    /// Threads in this pool that are currently executing a task will finish what
    /// they're doing until they check the channel, discovering that it has been
    /// disconnected from the sender and thus terminate their work loop.
    ///
    /// If other clones of this `ThreadPool` exist the sender will remain intact
    /// and tasks submitted to those clones will succeed, this includes pending
    /// `AsyncTask` instances as they hold an owned clone of the `ThreadPool`
    /// to re-submit awakened futures.
    ///
    /// This function additionally joins all workers after dropping the pool to
    /// wait for all work to finish.
    /// Blocks the current thread until there aren't any non-idle threads anymore.
    /// This function blocks until this `ThreadPool` completes all of its work,
    /// except if all threads are idle and the channel is empty at the time of
    /// calling this function, in which case the join will fast-return.
    /// If other live clones of this `ThreadPool` exist this behaves the same as
    /// calling [`join`](struct.ThreadPool.html#method.join) on a live `ThreadPool` as tasks submitted
    /// to one of the clones will be joined as well.
    ///
    /// The join utilizes a `Condvar` that is notified by workers when they complete a job and notice
    /// that the channel is currently empty and it was the last thread to finish the current
    /// generation of work (i.e. when incrementing the idle worker counter brings the value
    /// up to the total worker counter, meaning it's the last thread to become idle).
    pub fn shutdown_join(self) {
        self.inner_shutdown_join(None);
    }

    /// Destroy this `ThreadPool` by claiming ownership and dropping the value,
    /// causing the `Sender` to drop thus disconnecting the channel.
    /// Threads in this pool that are currently executing a task will finish what
    /// they're doing until they check the channel, discovering that it has been
    /// disconnected from the sender and thus terminate their work loop.
    ///
    /// If other clones of this `ThreadPool` exist the sender will remain intact
    /// and tasks submitted to those clones will succeed, this includes pending
    /// `AsyncTask` instances as they hold an owned clone of the `ThreadPool`
    /// to re-submit awakened futures.
    ///
    /// This function additionally joins all workers after dropping the pool to
    /// wait for all work to finish.
    /// Blocks the current thread until there aren't any non-idle threads anymore or until the
    /// specified time_out Duration passes, whichever happens first.
    /// This function blocks until this `ThreadPool` completes all of its work,
    /// (or until the time_out is reached) except if all threads are idle and the channel is
    /// empty at the time of calling this function, in which case the join will fast-return.
    /// If other live clones of this `ThreadPool` exist this behaves the same as
    /// calling [`join`](struct.ThreadPool.html#method.join) on a live `ThreadPool` as tasks submitted
    /// to one of the clones will be joined as well.
    ///
    /// The join utilizes a `Condvar` that is notified by workers when they complete a job and notice
    /// that the channel is currently empty and it was the last thread to finish the current
    /// generation of work (i.e. when incrementing the idle worker counter brings the value
    /// up to the total worker counter, meaning it's the last thread to become idle).
    pub fn shutdown_join_timeout(self, timeout: Duration) {
        self.inner_shutdown_join(Some(timeout));
    }

    /// Return the name of this pool, used as prefix for each worker thread.
    pub fn get_name(&self) -> &str {
        &self.worker_data.pool_name
    }

    /// Starts all core workers by creating core idle workers until the total worker count reaches the core count.
    ///
    /// Returns immediately if the current worker count is already >= core size.
    pub fn start_core_threads(&self) {
        let worker_count_data = &self.worker_data.worker_count_data;

        let core_size = self.core_size;
        let mut curr_worker_count = worker_count_data.worker_count.load(Ordering::Relaxed);
        if WorkerCountData::get_total_count(curr_worker_count) >= core_size {
            return;
        }

        loop {
            let witnessed = worker_count_data.try_increment_worker_count(
                curr_worker_count,
                INCREMENT_TOTAL | INCREMENT_IDLE,
                core_size,
            );

            if WorkerCountData::get_total_count(witnessed) >= core_size {
                return;
            }

            let worker = Worker::new(
                self.channel_data.receiver.clone(),
                Arc::clone(&self.worker_data),
                None,
            );

            worker.start(None);
            curr_worker_count = witnessed;
        }
    }

    #[inline]
    fn send_task_to_channel(&self, task: Job) -> Result<(), crossbeam_channel::SendError<Job>> {
        self.channel_data.sender.send(task)?;

        Ok(())
    }

    #[inline]
    fn inner_join(&self, time_out: Option<Duration>) {
        ThreadPool::_do_join(&self.worker_data, &self.channel_data.receiver, time_out);
    }

    #[inline]
    fn inner_shutdown_join(self, timeout: Option<Duration>) {
        let current_worker_data = self.worker_data.clone();
        let receiver = self.channel_data.receiver.clone();
        drop(self);
        ThreadPool::_do_join(&current_worker_data, &receiver, timeout);
    }

    #[inline]
    fn _do_join(
        current_worker_data: &Arc<WorkerData>,
        receiver: &crossbeam_channel::Receiver<Job>,
        time_out: Option<Duration>,
    ) {
        // no thread is currently doing any work, return
        if ThreadPool::is_idle(current_worker_data, receiver) {
            return;
        }

        let join_generation = current_worker_data.join_generation.load(Ordering::SeqCst);
        let guard = current_worker_data
            .join_notify_mutex
            .lock()
            .expect("could not get join notify mutex lock");

        match time_out {
            Some(time_out) => {
                let _ret_guard = current_worker_data
                    .join_notify_condvar
                    .wait_timeout_while(guard, time_out, |_| {
                        join_generation
                            == current_worker_data.join_generation.load(Ordering::Relaxed)
                            && !ThreadPool::is_idle(current_worker_data, receiver)
                    })
                    .expect("could not wait for join condvar");
            }
            None => {
                let _ret_guard = current_worker_data
                    .join_notify_condvar
                    .wait_while(guard, |_| {
                        join_generation
                            == current_worker_data.join_generation.load(Ordering::Relaxed)
                            && !ThreadPool::is_idle(current_worker_data, receiver)
                    })
                    .expect("could not wait for join condvar");
            }
        };

        // increment generation if current thread is first thread to be awakened from wait in current generation
        let _ = current_worker_data.join_generation.compare_exchange(
            join_generation,
            join_generation.wrapping_add(1),
            Ordering::SeqCst,
            Ordering::SeqCst,
        );
    }

    #[inline]
    fn is_idle(
        current_worker_data: &Arc<WorkerData>,
        receiver: &crossbeam_channel::Receiver<Job>,
    ) -> bool {
        let (current_worker_count, current_idle_count) =
            current_worker_data.worker_count_data.get_both();
        current_idle_count == current_worker_count && receiver.is_empty()
    }
}

impl Default for ThreadPool {
    /// create default ThreadPool with the core pool size being equal to the number of cpus
    /// and the max_size being twice the core size with a 60 second timeout
    fn default() -> Self {
        let num_cpus = num_cpus::get();
        ThreadPool::new(
            num_cpus,
            std::cmp::max(num_cpus, num_cpus * 2),
            Duration::from_secs(60),
        )
    }
}

/// A helper struct to aid creating a new `ThreadPool` using default values where no value was
/// explicitly specified.
#[derive(Default)]
pub struct Builder {
    name: Option<String>,
    core_size: Option<usize>,
    max_size: Option<usize>,
    keep_alive: Option<Duration>,
}

impl Builder {
    /// Create a new `Builder`.
    pub fn new() -> Builder {
        Builder::default()
    }

    /// Specify the name of the `ThreadPool` that will be used as prefix for the name of each worker thread.
    /// By default the name is "rusty_pool_x" with x being a static pool counter.
    pub fn name(mut self, name: String) -> Builder {
        self.name = Some(name);
        self
    }

    /// Specify the core pool size for the `ThreadPool`. The core pool size is the number of threads that stay alive
    /// for the entire lifetime of the `ThreadPool` or, to be more precise, its channel. These threads are spawned if
    /// a task is submitted to the `ThreadPool` and the current worker count is below the core pool size.
    pub fn core_size(mut self, size: usize) -> Builder {
        self.core_size = Some(size);
        self
    }

    /// Specify the maximum pool size this `ThreadPool` may scale up to. This numbers represents the maximum number
    /// of threads that may be alive at the same time within this pool. Additional threads above the core pool size
    /// only remain idle for the duration specified by the `keep_alive` parameter before terminating. If the core pool
    /// is full, the current pool size is below the max size and there are no idle threads then additional threads
    /// will be spawned.
    pub fn max_size(mut self, size: usize) -> Builder {
        self.max_size = Some(size);
        self
    }

    /// Specify the duration for which additional threads outside the core pool remain alive while not receiving any
    /// work before giving up and terminating.
    pub fn keep_alive(mut self, keep_alive: Duration) -> Builder {
        self.keep_alive = Some(keep_alive);
        self
    }

    /// Build the `ThreadPool` using the parameters previously supplied to this `Builder` using the number of CPUs as
    /// default core size if none provided, twice the core size as max size if none provided, 60 seconds keep_alive
    /// if none provided and the default naming (rusty_pool_{pool_number}) if none provided.
    /// This function calls [`ThreadPool::new`](struct.ThreadPool.html#method.new) or
    /// [`ThreadPool::new_named`](struct.ThreadPool.html#method.new_named) depending on whether a name was provided.
    ///
    /// # Panics
    ///
    /// Building might panic if the `max_size` is 0 or lower than `core_size` or exceeds half
    /// the size of usize. This restriction exists because two counters (total workers and
    /// idle counters) are stored within one AtomicUsize.
    pub fn build(self) -> ThreadPool {
        use std::cmp::{max, min};

        let core_size = self.core_size.unwrap_or_else(|| {
            let num_cpus = num_cpus::get();
            if let Some(max_size) = self.max_size {
                min(MAX_SIZE, min(num_cpus, max_size))
            } else {
                min(MAX_SIZE, num_cpus)
            }
        });
        // handle potential overflow: try using twice the core_size or return core_size
        let max_size = self
            .max_size
            .unwrap_or_else(|| min(MAX_SIZE, max(core_size, core_size * 2)));
        let keep_alive = self.keep_alive.unwrap_or_else(|| Duration::from_secs(60));

        if let Some(name) = self.name {
            ThreadPool::new_named(name, core_size, max_size, keep_alive)
        } else {
            ThreadPool::new(core_size, max_size, keep_alive)
        }
    }
}

#[derive(Clone)]
struct Worker {
    receiver: crossbeam_channel::Receiver<Job>,
    worker_data: Arc<WorkerData>,
    keep_alive: Option<Duration>,
}

impl Worker {
    fn new(
        receiver: crossbeam_channel::Receiver<Job>,
        worker_data: Arc<WorkerData>,
        keep_alive: Option<Duration>,
    ) -> Self {
        Worker {
            receiver,
            worker_data,
            keep_alive,
        }
    }

    fn start(self, task: Option<Job>) {
        let worker_name = format!(
            "{}_thread_{}",
            self.worker_data.pool_name,
            self.worker_data
                .worker_number
                .fetch_add(1, Ordering::Relaxed)
        );

        thread::Builder::new()
            .name(worker_name)
            .spawn(move || {
                let mut sentinel = Sentinel::new(&self);

                if let Some(task) = task {
                    self.exec_task_and_notify(&mut sentinel, task);
                }

                loop {
                    // the two functions return different error types, but since the error type doesn't matter it is mapped to unit to make them compatible
                    let received_task: Result<Job, _> = match self.keep_alive {
                        Some(keep_alive) => self.receiver.recv_timeout(keep_alive).map_err(|_| ()),
                        None => self.receiver.recv().map_err(|_| ()),
                    };

                    match received_task {
                        Ok(task) => {
                            // mark current as no longer idle and execute task
                            self.worker_data.worker_count_data.decrement_worker_idle();
                            self.exec_task_and_notify(&mut sentinel, task);
                        }
                        Err(_) => {
                            // either channel was broken because the sender disconnected or, if can_timeout is true, the Worker has not received any work during
                            // its keep_alive period and will now terminate, break working loop
                            break;
                        }
                    }
                }

                // can decrement both at once as the thread only gets here from an idle state
                // (if waiting for work and receiving an error)
                self.worker_data.worker_count_data.decrement_both();
            })
            .expect("could not spawn thread");
    }

    #[inline]
    fn exec_task_and_notify(&self, sentinel: &mut Sentinel, task: Job) {
        sentinel.is_working = true;
        task();
        sentinel.is_working = false;
        // can already mark as idle as this thread will continue the work loop
        self.mark_idle_and_notify_joiners_if_no_work();
    }

    #[inline]
    fn mark_idle_and_notify_joiners_if_no_work(&self) {
        let (old_total_count, old_idle_count) = self
            .worker_data
            .worker_count_data
            .increment_worker_idle_ret_both();
        // if the last task was the last one in the current generation,
        // i.e. if incrementing the idle count leads to the idle count
        // being equal to the total worker count, notify joiners
        if old_total_count == old_idle_count + 1 && self.receiver.is_empty() {
            let _lock = self
                .worker_data
                .join_notify_mutex
                .lock()
                .expect("could not get join notify mutex lock");
            self.worker_data.join_notify_condvar.notify_all();
        }
    }
}

/// Type that exists to manage worker exit on panic.
///
/// This type is constructed once per `Worker` and implements `Drop` to handle proper worker exit
/// in case the worker panics when executing the current task or anywhere else in its work loop.
/// If the `Sentinel` is dropped at the end of the worker's work loop and the current thread is
/// panicking, handle worker exit the same way as if the task completed normally (if the worker
/// panicked while executing a submitted task) then clone the worker and start it with an initial
/// task of `None`.
struct Sentinel<'s> {
    is_working: bool,
    worker_ref: &'s Worker,
}

impl Sentinel<'_> {
    fn new(worker_ref: &Worker) -> Sentinel<'_> {
        Sentinel {
            is_working: false,
            worker_ref,
        }
    }
}

impl Drop for Sentinel<'_> {
    fn drop(&mut self) {
        if thread::panicking() {
            if self.is_working {
                // worker thread panicked in the process of executing a submitted task,
                // run the same logic as if the task completed normally and mark it as
                // idle, since a clone of this worker will start the work loop as idle
                // thread
                self.worker_ref.mark_idle_and_notify_joiners_if_no_work();
            }

            let worker = self.worker_ref.clone();
            worker.start(None);
        }
    }
}

const WORKER_IDLE_MASK: usize = MAX_SIZE;
const INCREMENT_TOTAL: usize = 1 << (BITS / 2);
const INCREMENT_IDLE: usize = 1;

/// Struct that stores and handles an `AtomicUsize` that stores the total worker count
/// in the higher half of bits and the idle worker count in the lower half of bits.
/// This allows to to increment / decrement both counters in a single atomic operation.
#[derive(Default)]
struct WorkerCountData {
    worker_count: AtomicUsize,
}

impl WorkerCountData {
    fn get_total_worker_count(&self) -> usize {
        let curr_val = self.worker_count.load(Ordering::Relaxed);
        WorkerCountData::get_total_count(curr_val)
    }

    fn get_idle_worker_count(&self) -> usize {
        let curr_val = self.worker_count.load(Ordering::Relaxed);
        WorkerCountData::get_idle_count(curr_val)
    }

    fn get_both(&self) -> (usize, usize) {
        let curr_val = self.worker_count.load(Ordering::Relaxed);
        WorkerCountData::split(curr_val)
    }

    // keep for testing and completion's sake
    #[allow(dead_code)]
    fn increment_both(&self) -> (usize, usize) {
        let old_val = self
            .worker_count
            .fetch_add(INCREMENT_TOTAL | INCREMENT_IDLE, Ordering::Relaxed);
        WorkerCountData::split(old_val)
    }

    fn decrement_both(&self) -> (usize, usize) {
        let old_val = self
            .worker_count
            .fetch_sub(INCREMENT_TOTAL | INCREMENT_IDLE, Ordering::Relaxed);
        WorkerCountData::split(old_val)
    }

    fn try_increment_worker_total(&self, expected: usize, max_total: usize) -> usize {
        self.try_increment_worker_count(expected, INCREMENT_TOTAL, max_total)
    }

    fn try_increment_worker_count(
        &self,
        mut expected: usize,
        increment: usize,
        max_total: usize,
    ) -> usize {
        loop {
            match self.worker_count.compare_exchange_weak(
                expected,
                expected + increment,
                Ordering::Relaxed,
                Ordering::Relaxed,
            ) {
                Ok(witnessed) => return witnessed,
                Err(witnessed) if WorkerCountData::get_total_count(witnessed) >= max_total => {
                    return witnessed
                }
                Err(witnessed) => expected = witnessed,
            }
        }
    }

    // keep for testing and completion's sake
    #[allow(dead_code)]
    fn increment_worker_total(&self) -> usize {
        let old_val = self
            .worker_count
            .fetch_add(INCREMENT_TOTAL, Ordering::Relaxed);
        WorkerCountData::get_total_count(old_val)
    }

    // keep for testing and completion's sake
    #[allow(dead_code)]
    fn increment_worker_total_ret_both(&self) -> (usize, usize) {
        let old_val = self
            .worker_count
            .fetch_add(INCREMENT_TOTAL, Ordering::Relaxed);
        WorkerCountData::split(old_val)
    }

    // keep for testing and completion's sake
    #[allow(dead_code)]
    fn decrement_worker_total(&self) -> usize {
        let old_val = self
            .worker_count
            .fetch_sub(INCREMENT_TOTAL, Ordering::Relaxed);
        WorkerCountData::get_total_count(old_val)
    }

    // keep for testing and completion's sake
    #[allow(dead_code)]
    fn decrement_worker_total_ret_both(&self) -> (usize, usize) {
        let old_val = self
            .worker_count
            .fetch_sub(INCREMENT_TOTAL, Ordering::Relaxed);
        WorkerCountData::split(old_val)
    }

    // keep for testing and completion's sake
    #[allow(dead_code)]
    fn increment_worker_idle(&self) -> usize {
        let old_val = self
            .worker_count
            .fetch_add(INCREMENT_IDLE, Ordering::Relaxed);
        WorkerCountData::get_idle_count(old_val)
    }

    fn increment_worker_idle_ret_both(&self) -> (usize, usize) {
        let old_val = self
            .worker_count
            .fetch_add(INCREMENT_IDLE, Ordering::Relaxed);
        WorkerCountData::split(old_val)
    }

    fn decrement_worker_idle(&self) -> usize {
        let old_val = self
            .worker_count
            .fetch_sub(INCREMENT_IDLE, Ordering::Relaxed);
        WorkerCountData::get_idle_count(old_val)
    }

    // keep for testing and completion's sake
    #[allow(dead_code)]
    fn decrement_worker_idle_ret_both(&self) -> (usize, usize) {
        let old_val = self
            .worker_count
            .fetch_sub(INCREMENT_IDLE, Ordering::Relaxed);
        WorkerCountData::split(old_val)
    }

    #[inline]
    fn split(val: usize) -> (usize, usize) {
        let total_count = val >> (BITS / 2);
        let idle_count = val & WORKER_IDLE_MASK;
        (total_count, idle_count)
    }

    #[inline]
    fn get_total_count(val: usize) -> usize {
        val >> (BITS / 2)
    }

    #[inline]
    fn get_idle_count(val: usize) -> usize {
        val & WORKER_IDLE_MASK
    }
}

/// struct containing data shared between workers
struct WorkerData {
    pool_name: String,
    worker_count_data: WorkerCountData,
    worker_number: AtomicUsize,
    join_notify_condvar: Condvar,
    join_notify_mutex: Mutex<()>,
    join_generation: AtomicUsize,
}

struct ChannelData {
    sender: crossbeam_channel::Sender<Job>,
    receiver: crossbeam_channel::Receiver<Job>,
}

#[cfg(test)]
mod tests {

    use std::sync::{
        atomic::{AtomicUsize, Ordering},
        Arc,
    };
    use std::thread;
    use std::time::Duration;

    use super::Builder;
    use super::ThreadPool;
    use super::WorkerCountData;

    #[test]
    fn it_works() {
        let pool = ThreadPool::new(2, 10, Duration::from_secs(5));
        let count = Arc::new(AtomicUsize::new(0));

        let count1 = count.clone();
        pool.execute(move || {
            count1.fetch_add(1, Ordering::Relaxed);
            thread::sleep(std::time::Duration::from_secs(4));
        });
        let count2 = count.clone();
        pool.execute(move || {
            count2.fetch_add(1, Ordering::Relaxed);
            thread::sleep(std::time::Duration::from_secs(4));
        });
        let count3 = count.clone();
        pool.execute(move || {
            count3.fetch_add(1, Ordering::Relaxed);
            thread::sleep(std::time::Duration::from_secs(4));
        });
        let count4 = count.clone();
        pool.execute(move || {
            count4.fetch_add(1, Ordering::Relaxed);
            thread::sleep(std::time::Duration::from_secs(4));
        });
        thread::sleep(std::time::Duration::from_secs(20));
        let count5 = count.clone();
        pool.execute(move || {
            count5.fetch_add(1, Ordering::Relaxed);
            thread::sleep(std::time::Duration::from_secs(4));
        });
        let count6 = count.clone();
        pool.execute(move || {
            count6.fetch_add(1, Ordering::Relaxed);
            thread::sleep(std::time::Duration::from_secs(4));
        });
        let count7 = count.clone();
        pool.execute(move || {
            count7.fetch_add(1, Ordering::Relaxed);
            thread::sleep(std::time::Duration::from_secs(4));
        });
        let count8 = count.clone();
        pool.execute(move || {
            count8.fetch_add(1, Ordering::Relaxed);
            thread::sleep(std::time::Duration::from_secs(4));
        });
        thread::sleep(std::time::Duration::from_secs(20));

        let count = count.load(Ordering::Relaxed);
        let worker_count = pool.get_current_worker_count();

        assert_eq!(count, 8);
        // assert that non-core threads were dropped
        assert_eq!(worker_count, 2);
        assert_eq!(pool.get_idle_worker_count(), 2);
    }

    #[test]
    #[ignore]
    fn stress_test() {
        let pool = Arc::new(ThreadPool::new(3, 50, Duration::from_secs(30)));
        let counter = Arc::new(AtomicUsize::new(0));

        for _ in 0..5 {
            let pool_1 = pool.clone();
            let clone = counter.clone();
            pool.execute(move || {
                for _ in 0..160 {
                    let clone = clone.clone();
                    pool_1.execute(move || {
                        clone.fetch_add(1, Ordering::Relaxed);
                        thread::sleep(Duration::from_secs(10));
                    });
                }

                thread::sleep(Duration::from_secs(20));

                for _ in 0..160 {
                    let clone = clone.clone();
                    pool_1.execute(move || {
                        clone.fetch_add(1, Ordering::Relaxed);
                        thread::sleep(Duration::from_secs(10));
                    });
                }
            });
        }

        thread::sleep(Duration::from_secs(10));
        assert_eq!(pool.get_current_worker_count(), 50);

        pool.join();
        assert_eq!(counter.load(Ordering::Relaxed), 1600);
        thread::sleep(Duration::from_secs(31));
        assert_eq!(pool.get_current_worker_count(), 3);
    }

    #[test]
    fn test_join() {
        // use a thread pool with one thread max to make sure the second task starts after
        // pool.join() is called to make sure it joins future tasks as well
        let pool = ThreadPool::new(0, 1, Duration::from_secs(5));
        let counter = Arc::new(AtomicUsize::new(0));

        let clone_1 = counter.clone();
        pool.execute(move || {
            thread::sleep(Duration::from_secs(5));
            clone_1.fetch_add(1, Ordering::Relaxed);
        });

        let clone_2 = counter.clone();
        pool.execute(move || {
            thread::sleep(Duration::from_secs(5));
            clone_2.fetch_add(1, Ordering::Relaxed);
        });

        pool.join();

        assert_eq!(counter.load(Ordering::Relaxed), 2);
    }

    #[test]
    fn test_join_timeout() {
        let pool = ThreadPool::new(0, 1, Duration::from_secs(5));
        let counter = Arc::new(AtomicUsize::new(0));

        let clone = counter.clone();
        pool.execute(move || {
            thread::sleep(Duration::from_secs(10));
            clone.fetch_add(1, Ordering::Relaxed);
        });

        pool.join_timeout(Duration::from_secs(5));
        assert_eq!(counter.load(Ordering::Relaxed), 0);
        pool.join();
        assert_eq!(counter.load(Ordering::Relaxed), 1);
    }

    #[test]
    fn test_shutdown() {
        let pool = ThreadPool::new(1, 3, Duration::from_secs(5));
        let counter = Arc::new(AtomicUsize::new(0));

        let clone_1 = counter.clone();
        pool.execute(move || {
            thread::sleep(Duration::from_secs(5));
            clone_1.fetch_add(1, Ordering::Relaxed);
        });

        let clone_2 = counter.clone();
        pool.execute(move || {
            thread::sleep(Duration::from_secs(5));
            clone_2.fetch_add(1, Ordering::Relaxed);
        });

        let clone_3 = counter.clone();
        pool.execute(move || {
            thread::sleep(Duration::from_secs(5));
            clone_3.fetch_add(1, Ordering::Relaxed);
        });

        // since the pool only allows three threads this won't get the chance to run
        let clone_4 = counter.clone();
        pool.execute(move || {
            thread::sleep(Duration::from_secs(5));
            clone_4.fetch_add(1, Ordering::Relaxed);
        });

        pool.join_timeout(Duration::from_secs(2));
        pool.shutdown();

        thread::sleep(Duration::from_secs(5));

        assert_eq!(counter.load(Ordering::Relaxed), 3);
    }

    #[should_panic(
        expected = "max_size must be greater than 0 and greater or equal to the core pool size"
    )]
    #[test]
    fn test_panic_on_0_max_pool_size() {
        ThreadPool::new(0, 0, Duration::from_secs(2));
    }

    #[should_panic(
        expected = "max_size must be greater than 0 and greater or equal to the core pool size"
    )]
    #[test]
    fn test_panic_on_smaller_max_than_core_pool_size() {
        ThreadPool::new(10, 4, Duration::from_secs(2));
    }

    #[should_panic(expected = "max_size may not exceed")]
    #[test]
    fn test_panic_on_max_size_exceeds_half_usize() {
        ThreadPool::new(
            10,
            1 << ((std::mem::size_of::<usize>() * 8) / 2),
            Duration::from_secs(2),
        );
    }

    #[test]
    fn test_empty_join() {
        let pool = ThreadPool::new(3, 10, Duration::from_secs(10));
        pool.join();
    }

    #[test]
    fn test_join_when_complete() {
        let pool = ThreadPool::new(3, 10, Duration::from_secs(5));

        pool.execute(|| {
            thread::sleep(Duration::from_millis(5000));
        });

        thread::sleep(Duration::from_millis(5000));
        pool.join();
    }

    #[test]
    fn test_full_usage() {
        let pool = ThreadPool::new(5, 50, Duration::from_secs(10));

        for _ in 0..100 {
            pool.execute(|| {
                thread::sleep(Duration::from_secs(30));
            });
        }

        thread::sleep(Duration::from_secs(10));
        assert_eq!(pool.get_current_worker_count(), 50);

        pool.join();
        thread::sleep(Duration::from_secs(15));
        assert_eq!(pool.get_current_worker_count(), 5);
    }

    #[test]
    fn test_shutdown_join() {
        let pool = ThreadPool::new(1, 1, Duration::from_secs(5));
        let counter = Arc::new(AtomicUsize::new(0));

        let clone = counter.clone();
        pool.execute(move || {
            thread::sleep(Duration::from_secs(10));
            clone.fetch_add(1, Ordering::Relaxed);
        });

        pool.shutdown_join();
        assert_eq!(counter.load(Ordering::Relaxed), 1);
    }

    #[test]
    fn test_shutdown_join_timeout() {
        let pool = ThreadPool::new(1, 1, Duration::from_secs(5));
        let counter = Arc::new(AtomicUsize::new(0));

        let clone = counter.clone();
        pool.execute(move || {
            thread::sleep(Duration::from_secs(10));
            clone.fetch_add(1, Ordering::Relaxed);
        });

        pool.shutdown_join_timeout(Duration::from_secs(5));
        assert_eq!(counter.load(Ordering::Relaxed), 0);
    }

    #[test]
    fn test_empty_shutdown_join() {
        let pool = ThreadPool::new(1, 5, Duration::from_secs(5));
        pool.shutdown_join();
    }

    #[test]
    fn test_shutdown_core_pool() {
        let pool = ThreadPool::new(5, 5, Duration::from_secs(1));
        let counter = Arc::new(AtomicUsize::new(0));
        let worker_data = pool.worker_data.clone();

        for _ in 0..7 {
            let clone = counter.clone();
            pool.execute(move || {
                thread::sleep(Duration::from_secs(2));
                clone.fetch_add(1, Ordering::Relaxed);
            });
        }

        assert_eq!(pool.get_current_worker_count(), 5);
        assert_eq!(pool.get_idle_worker_count(), 0);
        pool.shutdown_join();
        assert_eq!(counter.load(Ordering::Relaxed), 7);

        // give the workers time to exit
        thread::sleep(Duration::from_millis(50));
        assert_eq!(worker_data.worker_count_data.get_total_worker_count(), 0);
        assert_eq!(worker_data.worker_count_data.get_idle_worker_count(), 0);
    }

    #[test]
    fn test_shutdown_idle_core_pool() {
        let pool = ThreadPool::new(5, 5, Duration::from_secs(1));
        let counter = Arc::new(AtomicUsize::new(0));
        let worker_data = pool.worker_data.clone();

        for _ in 0..5 {
            let clone = counter.clone();
            pool.execute(move || {
                clone.fetch_add(1, Ordering::Relaxed);
            });
        }

        pool.shutdown_join();
        assert_eq!(counter.load(Ordering::Relaxed), 5);

        // give the workers time to exit
        thread::sleep(Duration::from_millis(50));
        assert_eq!(worker_data.worker_count_data.get_total_worker_count(), 0);
        assert_eq!(worker_data.worker_count_data.get_idle_worker_count(), 0);
    }

    #[test]
    fn test_shutdown_on_complete() {
        let pool = ThreadPool::new(3, 10, Duration::from_secs(5));

        pool.execute(|| {
            thread::sleep(Duration::from_millis(5000));
        });

        thread::sleep(Duration::from_millis(5000));
        pool.shutdown_join();
    }

    #[test]
    fn test_shutdown_after_complete() {
        let pool = ThreadPool::new(3, 10, Duration::from_secs(5));

        pool.execute(|| {
            thread::sleep(Duration::from_millis(5000));
        });

        thread::sleep(Duration::from_millis(7000));
        pool.shutdown_join();
    }

    #[test]
    fn worker_count_test() {
        let worker_count_data = WorkerCountData::default();

        assert_eq!(worker_count_data.get_total_worker_count(), 0);
        assert_eq!(worker_count_data.get_idle_worker_count(), 0);

        worker_count_data.increment_both();

        assert_eq!(worker_count_data.get_total_worker_count(), 1);
        assert_eq!(worker_count_data.get_idle_worker_count(), 1);

        for _ in 0..10 {
            worker_count_data.increment_both();
        }

        assert_eq!(worker_count_data.get_total_worker_count(), 11);
        assert_eq!(worker_count_data.get_idle_worker_count(), 11);

        for _ in 0..15 {
            worker_count_data.increment_worker_total();
        }

        for _ in 0..7 {
            worker_count_data.increment_worker_idle();
        }

        assert_eq!(worker_count_data.get_total_worker_count(), 26);
        assert_eq!(worker_count_data.get_idle_worker_count(), 18);
        assert_eq!(worker_count_data.get_both(), (26, 18));

        for _ in 0..5 {
            worker_count_data.decrement_both();
        }

        assert_eq!(worker_count_data.get_total_worker_count(), 21);
        assert_eq!(worker_count_data.get_idle_worker_count(), 13);

        for _ in 0..13 {
            worker_count_data.decrement_worker_total();
        }

        for _ in 0..4 {
            worker_count_data.decrement_worker_idle();
        }

        assert_eq!(worker_count_data.get_total_worker_count(), 8);
        assert_eq!(worker_count_data.get_idle_worker_count(), 9);

        for _ in 0..456789 {
            worker_count_data.increment_worker_total();
        }

        assert_eq!(worker_count_data.get_total_worker_count(), 456797);
        assert_eq!(worker_count_data.get_idle_worker_count(), 9);
        assert_eq!(worker_count_data.get_both(), (456797, 9));

        for _ in 0..23456 {
            worker_count_data.increment_worker_idle();
        }

        assert_eq!(worker_count_data.get_total_worker_count(), 456797);
        assert_eq!(worker_count_data.get_idle_worker_count(), 23465);

        for _ in 0..150000 {
            worker_count_data.decrement_worker_total();
        }

        assert_eq!(worker_count_data.get_total_worker_count(), 306797);
        assert_eq!(worker_count_data.get_idle_worker_count(), 23465);

        for _ in 0..10000 {
            worker_count_data.decrement_worker_idle();
        }

        assert_eq!(worker_count_data.get_total_worker_count(), 306797);
        assert_eq!(worker_count_data.get_idle_worker_count(), 13465);
    }

    #[test]
    fn test_try_increment_worker_total() {
        let worker_count_data = WorkerCountData::default();

        let witness = worker_count_data.try_increment_worker_total(0, 5);
        assert_eq!(witness, 0);
        assert_eq!(worker_count_data.get_total_worker_count(), 1);
        assert_eq!(worker_count_data.get_idle_worker_count(), 0);

        let witness = worker_count_data.try_increment_worker_total(0, 5);
        assert_eq!(witness, 0x0000_0001_0000_0000);
        assert_eq!(worker_count_data.get_total_worker_count(), 2);
        assert_eq!(worker_count_data.get_idle_worker_count(), 0);

        worker_count_data.try_increment_worker_total(2, 5);
        worker_count_data.try_increment_worker_total(2, 5);
        worker_count_data.try_increment_worker_total(4, 5);
        worker_count_data.try_increment_worker_total(4, 5);
        let witness = worker_count_data.try_increment_worker_total(2, 5);
        assert_eq!(WorkerCountData::get_total_count(witness), 5);
        assert_eq!(WorkerCountData::get_idle_count(witness), 0);
        assert_eq!(worker_count_data.get_total_worker_count(), 5);
        assert_eq!(worker_count_data.get_idle_worker_count(), 0);

        let worker_count_data = Arc::new(worker_count_data);

        let mut join_handles = Vec::with_capacity(5);
        for _ in 0..5 {
            let worker_count_data = worker_count_data.clone();
            let join_handle = thread::spawn(move || {
                for i in 0..5 {
                    worker_count_data.try_increment_worker_total(5 + i, 15);
                }
            });

            join_handles.push(join_handle);
        }

        for join_handle in join_handles {
            join_handle.join().unwrap();
        }

        assert_eq!(worker_count_data.get_total_worker_count(), 15);
        assert_eq!(worker_count_data.get_idle_worker_count(), 0);
    }

    #[test]
    fn test_join_enqueued_task() {
        let pool = ThreadPool::new(3, 50, Duration::from_secs(20));
        let counter = Arc::new(AtomicUsize::new(0));

        for _ in 0..160 {
            let clone = counter.clone();
            pool.execute(move || {
                thread::sleep(Duration::from_secs(10));
                clone.fetch_add(1, Ordering::Relaxed);
            });
        }

        thread::sleep(Duration::from_secs(5));
        assert_eq!(pool.get_current_worker_count(), 50);

        pool.join();
        assert_eq!(counter.load(Ordering::Relaxed), 160);
        thread::sleep(Duration::from_secs(21));
        assert_eq!(pool.get_current_worker_count(), 3);
    }

    #[test]
    fn test_panic_all() {
        let pool = ThreadPool::new(3, 10, Duration::from_secs(2));

        for _ in 0..10 {
            pool.execute(|| {
                panic!("test");
            })
        }

        pool.join();
        thread::sleep(Duration::from_secs(5));
        assert_eq!(pool.get_current_worker_count(), 3);
        assert_eq!(pool.get_idle_worker_count(), 3);
    }

    #[test]
    fn test_panic_some() {
        let pool = ThreadPool::new(3, 10, Duration::from_secs(5));
        let counter = Arc::new(AtomicUsize::new(0));

        for i in 0..10 {
            let clone = counter.clone();
            pool.execute(move || {
                if i < 3 || i % 2 == 0 {
                    thread::sleep(Duration::from_secs(5));
                    clone.fetch_add(1, Ordering::Relaxed);
                } else {
                    thread::sleep(Duration::from_secs(5));
                    panic!("test");
                }
            })
        }

        pool.join();
        assert_eq!(counter.load(Ordering::Relaxed), 6);
        assert_eq!(pool.get_current_worker_count(), 10);
        assert_eq!(pool.get_idle_worker_count(), 10);
        thread::sleep(Duration::from_secs(10));
        assert_eq!(pool.get_current_worker_count(), 3);
        assert_eq!(pool.get_idle_worker_count(), 3);
    }

    #[test]
    fn test_panic_all_core_threads() {
        let pool = ThreadPool::new(3, 3, Duration::from_secs(1));
        let counter = Arc::new(AtomicUsize::new(0));

        for _ in 0..3 {
            pool.execute(|| {
                panic!("test");
            })
        }

        pool.join();

        for i in 0..10 {
            let clone = counter.clone();
            pool.execute(move || {
                if i < 3 || i % 2 == 0 {
                    clone.fetch_add(1, Ordering::Relaxed);
                } else {
                    thread::sleep(Duration::from_secs(5));
                    panic!("test");
                }
            })
        }

        pool.join();
        assert_eq!(counter.load(Ordering::Relaxed), 6);
        assert_eq!(pool.get_current_worker_count(), 3);
        assert_eq!(pool.get_idle_worker_count(), 3);
    }

    #[test]
    fn test_drop_all_receivers() {
        let pool = ThreadPool::new(0, 3, Duration::from_secs(5));
        let counter = Arc::new(AtomicUsize::new(0));

        for _ in 0..3 {
            let clone = counter.clone();
            pool.execute(move || {
                clone.fetch_add(1, Ordering::Relaxed);
            })
        }

        pool.join();
        assert_eq!(counter.load(Ordering::Relaxed), 3);
        thread::sleep(Duration::from_secs(10));
        assert_eq!(pool.get_current_worker_count(), 0);

        for _ in 0..3 {
            let clone = counter.clone();
            pool.execute(move || {
                clone.fetch_add(1, Ordering::Relaxed);
            })
        }

        pool.join();
        assert_eq!(counter.load(Ordering::Relaxed), 6);
    }

    #[test]
    fn test_evaluate() {
        let pool = ThreadPool::new(0, 3, Duration::from_secs(5));

        let count = AtomicUsize::new(0);

        let handle = pool.evaluate(move || {
            count.fetch_add(1, Ordering::Relaxed);
            thread::sleep(Duration::from_secs(5));
            count.fetch_add(1, Ordering::Relaxed)
        });

        let result = handle.await_complete();
        assert_eq!(result, 1);
    }

    #[test]
    fn test_multiple_evaluate() {
        let pool = ThreadPool::new(0, 3, Duration::from_secs(5));

        let count = AtomicUsize::new(0);
        let handle_1 = pool.evaluate(move || {
            for _ in 0..10000 {
                count.fetch_add(1, Ordering::Relaxed);
            }

            thread::sleep(Duration::from_secs(5));

            for _ in 0..10000 {
                count.fetch_add(1, Ordering::Relaxed);
            }

            count.load(Ordering::Relaxed)
        });

        let handle_2 = pool.evaluate(move || {
            let result = handle_1.await_complete();
            let mut count = result;

            count += 15000;

            thread::sleep(Duration::from_secs(5));

            count += 20000;

            count
        });

        let result = handle_2.await_complete();
        assert_eq!(result, 55000);
    }

    #[should_panic(expected = "could not receive message because channel was cancelled")]
    #[test]
    fn test_evaluate_panic() {
        let pool = Builder::new().core_size(5).max_size(50).build();

        let handle = pool.evaluate(|| {
            let x = 3;

            if x == 3 {
                panic!("expected panic")
            }

            return x;
        });

        handle.await_complete();
    }

    #[test]
    fn test_complete_fut() {
        let pool = ThreadPool::new(0, 3, Duration::from_secs(5));

        async fn async_fn() -> i8 {
            8
        }

        let fut = async_fn();
        let handle = pool.complete(fut);

        assert_eq!(handle.await_complete(), 8);
    }

    #[cfg(feature = "async")]
    #[test]
    fn test_spawn() {
        let pool = ThreadPool::default();

        async fn add(x: i32, y: i32) -> i32 {
            x + y
        }

        async fn multiply(x: i32, y: i32) -> i32 {
            x * y
        }

        let count = Arc::new(AtomicUsize::new(0));
        let clone = count.clone();
        pool.spawn(async move {
            let a = add(2, 3).await; // 5
            let b = add(2, a).await; // 7
            let c = multiply(2, b).await; // 14
            let d = multiply(a, add(2, 1).await).await; // 15
            let e = add(c, d).await; // 29

            clone.fetch_add(e as usize, Ordering::Relaxed);
        });

        pool.join();
        assert_eq!(count.load(Ordering::Relaxed), 29);
    }

    #[cfg(feature = "async")]
    #[test]
    fn test_spawn_await() {
        let pool = ThreadPool::default();

        async fn sub(x: i32, y: i32) -> i32 {
            x - y
        }

        async fn div(x: i32, y: i32) -> i32 {
            x / y
        }

        let handle = pool.spawn_await(async {
            let a = sub(120, 10).await; // 110
            let b = div(sub(a, 10).await, 4).await; // 25
            div(sub(b, div(10, 2).await).await, 5).await // 4
        });

        assert_eq!(handle.await_complete(), 4)
    }

    #[test]
    fn test_drop_oneshot_receiver() {
        let pool = Builder::new().core_size(1).max_size(1).build();

        let handle = pool.evaluate(|| {
            thread::sleep(Duration::from_secs(5));
            5
        });

        drop(handle);
        thread::sleep(Duration::from_secs(10));
        let current_thread_index = pool.worker_data.worker_number.load(Ordering::Relaxed);
        // current worker number of 2 means that one worker has started (initial number is 1 -> first worker gets and increments number)
        // indicating that the worker did not panic else it would have been replaced.
        assert_eq!(current_thread_index, 2);
    }

    #[test]
    fn test_builder_max_size() {
        Builder::new().max_size(1).build();
    }

    #[test]
    fn test_multi_thread_join() {
        let pool = ThreadPool::default();
        let count = Arc::new(AtomicUsize::new(0));

        let clone1 = count.clone();
        pool.execute(move || {
            thread::sleep(Duration::from_secs(10));
            clone1.fetch_add(1, Ordering::Relaxed);
        });

        let clone2 = count.clone();
        pool.execute(move || {
            thread::sleep(Duration::from_secs(10));
            clone2.fetch_add(1, Ordering::Relaxed);
        });

        let clone3 = count.clone();
        pool.execute(move || {
            thread::sleep(Duration::from_secs(10));
            clone3.fetch_add(1, Ordering::Relaxed);
        });

        let pool2 = pool.clone();
        let clone4 = count.clone();
        thread::spawn(move || {
            thread::sleep(Duration::from_secs(5));
            pool2.execute(move || {
                thread::sleep(Duration::from_secs(15));
                clone4.fetch_add(2, Ordering::Relaxed);
            });
        });

        let pool3 = pool.clone();
        let pool4 = pool.clone();
        let pool5 = pool.clone();
        let h1 = thread::spawn(move || {
            pool3.join();
        });
        let h2 = thread::spawn(move || {
            pool4.join();
        });
        let h3 = thread::spawn(move || {
            pool5.join();
        });
        h1.join().unwrap();
        h2.join().unwrap();
        h3.join().unwrap();

        assert_eq!(count.load(Ordering::Relaxed), 5);
    }

    #[test]
    fn test_start_core_threads() {
        let pool = Builder::new().core_size(5).build();
        pool.start_core_threads();
        assert_eq!(pool.get_current_worker_count(), 5);
        assert_eq!(pool.get_idle_worker_count(), 5);
    }

    #[test]
    fn test_start_and_use_core_threads() {
        let pool = Builder::new()
            .core_size(5)
            .max_size(10)
            .keep_alive(Duration::from_secs(u64::MAX))
            .build();
        pool.start_core_threads();
        let result = pool.evaluate(|| 5 + 5).await_complete();
        assert_eq!(result, 10);
        assert_eq!(pool.get_current_worker_count(), 5);
    }
}