shared_resource_pool_builder/

lib.rs

//! # Shared Resource Pool Builder
//!
//! A producer-consumer thread pool builder that will eventually consume all items
//! sequentially with a shared resource.
//!
//! ## Code example
//!
//! The purpose of this library is best described with an example, so let's get
//! straight into it:
//!
//! ```rust
//! use shared_resource_pool_builder::SharedResourcePoolBuilder;
//!
//! // Define a pool builder with a Vector as shared resource, and an action that
//! // should be executed sequentially over all items. Note that the second
//! // parameter of this function is a shared consumer function that takes two
//! // parameters: The shared resource and the items it will be used on. These
//! // items will be returned from the pool consumers.
//! let pool_builder = SharedResourcePoolBuilder::new(
//!     Vec::new(),
//!     |vec, i| vec.push(i)
//! );
//!
//! // Create a producer-consumer thread pool that does some work. In this case,
//! // send the numbers 0 to 2 to the consumer. There, they will be multiplied by
//! // 10. Note that the first parameter is a producer function that takes a
//! // Sender like object, like [`std::sync::mpsc::Sender`]. Every item that gets
//! // sent will be processed by the consumer, which is the second parameter to
//! // this function. This function expects an object of the same type that gets
//! // sent by the producer. The consumer is expected to return an object of the
//! // type that the shared consumer takes as the second parameter and will
//! // ultimately used on the shared resource.
//! let pool_1 = pool_builder
//!     .create_pool(
//!         |tx| (0..=2).for_each(|i| tx.send(i).unwrap()),
//!         |i| i * 10
//!     );
//!
//! // Create a second pool. Here, the numbers 3 to 5 will be produced, multiplied
//! // by 2, and being processed by the shared consumer function.
//! let pool_2 = pool_builder
//!     .create_pool(
//!         |tx| (3..=5).for_each(|i| tx.send(i).unwrap()),
//!         |i| i * 2
//!     );
//!
//! // Wait for a specific pool to finish before continuing ...
//! pool_1.join().unwrap();
//!
//! // ... or wait for all pools and the shared consumer to finish their work at
//! // once and return the shared resource. Afterwards, the pool builder can no
//! // longer be used, since the shared resource gets moved.
//! let result = {
//!     let mut result = pool_builder.join().unwrap();
//!
//!     // By default, the pool consumers run in as many threads as there are
//!     // cores in the machine, so the result may not be in the same order as
//!     // they were programmed.
//!     result.sort();
//!     result
//! };
//!
//! assert_eq!(result, vec![0, 6, 8, 10, 10, 20]);
//! ```
//!
//! ## Motivation
//!
//! Imagine you have a huge list of items that need to be processed. Every item
//! can be processed independently, so the natural thing to do is using a thread
//! pool to parallelize the work. But now imagine that the resulting items need to
//! be used together with a resource that does not work on multiple threads. The
//! resulting items will have to be processed sequentially, so the resource does
//! not have to be shared with multiple threads.
//!
//! As a more concrete example, imagine a program that uses a SQLite database for
//! storing computational intensive results. Before doing the actual work, you
//! want to remove obsolete results from the database. Then you need to collect
//! all new data that need to get processed. At last, you want all new data to be
//! actually processed.
//!
//! Normally, this involves three sequential steps: Cleaning, collecting, and
//! processing. These steps need to be sequential because writing operations on
//! the same SQLite database can only be done by one thread at a time. You might
//! want to implement synchronization, so that one thread writes and all
//! additional threads are blocked and wait for their turn. But this can be error
//! prone if not done correctly. You will encounter random panics of locked or
//! busy databases. Furthermore, you lose the ability to use prepared statements
//! efficiently.
//!
//! Enter `shared-resource-pool-builder`. With this, you have the ability to
//! define a *shared resource* and a *shared consumer function*. From this builder
//! you can create producer-consumer pools. The consumed items will then be
//! sequentially given to the shared consumer function to apply the result to the
//! shared resource.
//!
//! The pool consumers will all run within a shared thread pool, so you need not
//! to worry about thrashing your system. You can even limit the number of items
//! that get processed in parallel.
//!
//! To stay with the database example, this means you can define a pool builder
//! with the database connection as the shared resource and a shared consumer
//! function that will remove, insert, or update items. You can do that with an
//! enum, for example.
//!
//! Then, for the cleaning step, you create a pool that produces all items from
//! the database and consumes them by returning an object that causes the item to
//! be either deleted (if obsolete) or ignored by the shared consumer.
//!
//! Next, you can create a pool that produces all new items and consumes them by
//! creating an insert action with each item.
//!
//! Depending on the database layout, these two pools can even be run in parallel.
//! Thanks to the shared consumer, only one delete or insert will run at the same
//! time.
//!
//! Again, depending on the layout, you just need to wait for the inserting pool
//! to finish and create yet another pool that produces all new items that needs
//! to be processed, and consumes them by doing the actual work and returning an
//! appropriate update object for the shared consumer. In the meanwhile, the
//! cleaning pool might as well continue its work.
//!
//! Eventually, you wait for all pools to finish before terminating the program.
//!
//! This way, you do not need to worry about synchronizing multiple writer threads
//! or multiple open database connections. Just split the work so the
//! computational intensive tasks get done in the pool consumers and make the
//! shared consumer just do the finalization.

use std::sync::mpsc::{channel, sync_channel, Receiver, Sender, SyncSender};
use std::sync::{Arc, Condvar, Mutex};
use std::thread;
use std::thread::JoinHandle;

use threadpool::ThreadPool;

use crate::job::JobCounter;
pub use crate::job::{Job, JobHandle};
use crate::senderlike::SenderLike;

mod job;
mod senderlike;

/// The builder to create pools on a shared resource.
pub struct SharedResourcePoolBuilder<SType, SR> {
    tx: SType,
    handler_thread: JoinHandle<SR>,
    consumer_pool: ThreadPool,
}

impl<SType, Arg, SR> SharedResourcePoolBuilder<SType, SR>
where
    Arg: Send + 'static,
    SType: SenderLike<Item = Job<Arg>> + Clone + Send + 'static,
    SR: Send + 'static,
{
    fn init<SC>(
        tx: SType,
        rx: Receiver<Job<Arg>>,
        mut shared_resource: SR,
        mut shared_consumer_fn: SC,
    ) -> Self
    where
        SC: FnMut(&mut SR, Arg) -> () + Send + Sync + 'static,
    {
        let join_handle = thread::spawn(move || {
            for job in rx {
                shared_consumer_fn(&mut shared_resource, job.0);
            }
            shared_resource
        });

        let consumer_pool = threadpool::Builder::new().build();

        Self {
            tx,
            handler_thread: join_handle,
            consumer_pool,
        }
    }

    /// Creates an unbounded producer-consumer pool.
    ///
    /// This method takes two parameters:
    ///
    /// -   The producer function
    ///
    ///     This function will generate the items to be further processed by the consumer. It must
    ///     take one parameter, which is a sender like object like [`Sender`]. To generate an item
    ///     for the consumer, use the `send()` method of the sender.
    ///
    ///     The return type of this function will be ignored, i.e. it is `()`.
    ///
    ///     By design, this function will run in only one thread. If you want it to run in multiple
    ///     threads, you need to implement that by yourself. The preferred way is to run only a
    ///     cheap listing algorithm in the producer and let the consumer do the computational
    ///     intensive tasks, which will by default run within a thread pool.
    ///
    /// -   The consumer function
    ///
    ///     This function takes one parameter and will be called for each item that was sent by the
    ///     producer. The return type must be the same type that is used by the shared consumer as
    ///     defined by the [`Self::new()`] method.
    ///
    ///     By design, the consumer functions will be run within a thread pool that is shared with
    ///     every other pool consumers created by this builder. The number of threads is the number
    ///     of cores, as defined by the default value of [`threadpool::Builder::num_threads()`].
    ///
    /// The message channel, in which the producer sends and the consumer receives the items, is
    /// unlimited with this function (in other words, it uses [`channel()`]). On modern systems and
    /// "typical" use-cases, this should not be a problem. If however your system is low on memory
    /// or your producer generates millions over millions of items, then you might be interested in
    /// the [bounded](`Self::create_pool_bounded()`) variant of this method.
    ///
    /// # Example
    ///
    /// Assuming that `heavy_algorithm()` converts an integer to an object that can be used with
    /// the shared consumer function, a pool creation might look like this:
    ///
    /// ```rust
    /// # use std::error::Error;
    /// # use std::sync::mpsc::Sender;
    /// # use shared_resource_pool_builder::SharedResourcePoolBuilder;
    /// #
    /// # fn heavy_algorithm(i: i32) -> i32 { i }
    /// #
    /// # fn example() {
    /// # let pool_builder = SharedResourcePoolBuilder::new(true, |res, item|());
    /// pool_builder.create_pool(
    ///     |tx| (0..10).for_each(|i| tx.send(i).unwrap()),
    ///     |i| heavy_algorithm(i),
    /// );
    /// # }
    /// ```
    pub fn create_pool<P, PArg, C>(&self, producer_fn: P, consumer_fn: C) -> JobHandle
    where
        P: Fn(Sender<PArg>) -> () + Send + 'static,
        PArg: Send + 'static,
        C: Fn(PArg) -> Arg + Clone + Send + Sync + 'static,
    {
        let (tx, rx) = channel::<PArg>();
        self.init_pool(tx, rx, producer_fn, consumer_fn)
    }

    /// Creates a bounded producer-consumer pool.
    ///
    /// This method is nearly identical to its [unbounded](`Self::create_pool()`) variant. For a
    /// detailled description of the producer and consumer parameters, please look there.
    ///
    /// The difference is, that this function takes an additional integer parameter, which limits
    /// the size of the message channel, that is used by the producer and consumer (in other words,
    /// it uses [`sync_channel()`]). If the channel is full, the producer will block until the
    /// consumer takes at least one item. This can be useful if you expect a huge amount of items
    /// to be generated, or if your system is low on memory.
    ///
    /// # Example
    ///
    /// Assuming that `crazy_producer()` generates a huge amount of integer values, and that
    /// `heavy_algorithm()` converts an integer to an object that can be used with the shared
    /// consumer function, a bounded pool creation with a buffer of 100 items might look like this:
    ///
    /// ```rust
    /// # use std::error::Error;
    /// # use std::sync::mpsc::Sender;
    /// # use shared_resource_pool_builder::SharedResourcePoolBuilder;
    /// #
    /// # fn crazy_producer() -> Vec<i32> { vec![] }
    /// # fn heavy_algorithm(i: i32) -> i32 { i }
    /// #
    /// # fn example() {
    /// # let pool_builder = SharedResourcePoolBuilder::new(true, |res, item|());
    /// pool_builder.create_pool_bounded(
    ///     100,
    ///     |tx| crazy_producer().into_iter().for_each(|i| tx.send(i).unwrap()),
    ///     |i| heavy_algorithm(i),
    /// );
    /// # }
    /// ```
    pub fn create_pool_bounded<P, PArg, C>(
        &self,
        bound: usize,
        producer_fn: P,
        consumer_fn: C,
    ) -> JobHandle
    where
        P: Fn(SyncSender<PArg>) -> () + Send + 'static,
        PArg: Send + 'static,
        C: Fn(PArg) -> Arg + Clone + Send + Sync + 'static,
    {
        let (tx, rx) = sync_channel::<PArg>(bound);
        self.init_pool(tx, rx, producer_fn, consumer_fn)
    }

    fn init_pool<P, PArg, PType, C>(
        &self,
        tx: PType,
        rx: Receiver<PArg>,
        producer_fn: P,
        consumer_fn: C,
    ) -> JobHandle
    where
        PType: SenderLike<Item = PArg> + Send + 'static,
        P: Fn(PType) -> () + Send + 'static,
        PArg: Send + 'static,
        C: Fn(PArg) -> Arg + Clone + Send + Sync + 'static,
    {
        let producer_thread = thread::spawn(move || producer_fn(tx));

        let job_counter = Arc::new((Mutex::new(0), Condvar::new()));

        let consumer_thread = {
            let pool = self.consumer_pool.clone();
            let job_counter = Arc::clone(&job_counter);
            let tx = self.tx.clone();
            thread::spawn(move || {
                for item in rx {
                    let tx = tx.clone();
                    let consumer_fn = consumer_fn.clone();
                    let job_counter = JobCounter::new(Arc::clone(&job_counter));
                    pool.execute(move || {
                        let job = Job(consumer_fn(item), job_counter);
                        tx.send(job).unwrap();
                    });
                }
            })
        };

        let join_handle = thread::spawn(move || {
            producer_thread.join().unwrap();
            consumer_thread.join().unwrap();
        });

        JobHandle::new(join_handle, job_counter)
    }

    /// Send one single item to the shared consumer.
    ///
    /// This method can be used to communicate with the shared resource, before creating another
    /// pool. Maybe you just want to add another item to the shared consumer. Or you want to use
    /// this method to trigger an alternate bevahior of the shared consumer.
    ///
    /// Internally, this method behaves much like the [`Self::create_pool()`] method. It returns a
    /// [`JobHandle`], which can be waited on with [`JobHandle::join()`]. The item is sent to the
    /// message queue of the pool builder and might not be consumed immediately if there are other
    /// items waiting.
    ///
    /// # Examples
    ///
    /// ## Add another item
    ///
    /// In the following example, in addition to summing up 0, 1, and 2, as well as 4, 5, and 6, we
    /// add a single 3 to the result:
    ///
    /// ```rust
    /// # use shared_resource_pool_builder::SharedResourcePoolBuilder;
    /// #
    /// let pool_builder = SharedResourcePoolBuilder::new(0, |sum, i| *sum += i);
    ///
    /// pool_builder.create_pool(
    ///     |tx| vec![0, 1, 2].into_iter().for_each(|i| tx.send(i).unwrap()),
    ///     |i| i,
    /// );
    ///
    /// pool_builder.oneshot(3);
    ///
    /// pool_builder.create_pool(
    ///     |tx| vec![4, 5, 6].into_iter().for_each(|i| tx.send(i).unwrap()),
    ///     |i| i,
    /// );
    ///
    /// let result = pool_builder.join().unwrap();
    ///
    /// assert_eq!(result, 21);
    /// ```
    ///
    /// ## Trigger alternate behavior
    ///
    /// In the following example, we change the behavior of the shared consumer in the middle of
    /// the execution:
    ///
    /// ```rust
    /// # use shared_resource_pool_builder::SharedResourcePoolBuilder;
    /// #
    /// let pool_builder = SharedResourcePoolBuilder::new(
    ///     // Here we define our shared resource to be a tuple. The second element will determine
    ///     // our current behavior and can be altered in the shared consumer function.
    ///     (0, true),
    ///
    ///     // The whole tuple must be used in the shared consumer. Add or subtract the received
    ///     // value `i`, depending on the state of `adding`. If `None` is received, swap the state
    ///     // variable, so that upcoming values will be handled by the alternate behavior.
    ///     |(sum, adding), i| {
    ///         match i {
    ///             Some(i) => {
    ///                 if *adding {
    ///                     *sum += i;
    ///                 } else {
    ///                     *sum -= i;
    ///                 }
    ///             }
    ///             None => {
    ///                 *adding = !*adding;
    ///             }
    ///         }
    ///     },
    /// );
    ///
    /// // First we add some numbers
    /// pool_builder.create_pool(
    ///     |tx| vec![0, 1, 2].into_iter().for_each(|i| tx.send(Some(i)).unwrap()),
    ///     |i| i,
    /// ).join().unwrap();
    ///
    /// // Swap summing behavior
    /// pool_builder.oneshot(None).join().unwrap();
    ///
    /// // Now we subtract the same numbers again, with the same code as before
    /// pool_builder.create_pool(
    ///     |tx| vec![0, 1, 2].into_iter().for_each(|i| tx.send(Some(i)).unwrap()),
    ///     |i| i,
    /// );
    ///
    /// // Remember that we defined a boolean in our shared resource tuple. We are not interested
    /// // in this one anymore, so we explicitly ignore it here.
    /// let (result, _) = pool_builder.join().unwrap();
    ///
    /// // Since we subtracted the same amount as we added, the result is now 0
    /// assert_eq!(result, 0);
    ///
    /// // Note that we joined the first pool and the oneshot to await them to be finished. In this
    /// // simple example, it would normally not be necessary, since sending merely three items
    /// // happens quite immediately and the shared consumer handles all items sequentially.
    /// // Nevertheless, there could be a race condition if for some reason the swapping is
    /// // triggered before all items could be added. In more complex scenarios, care should be
    /// // taken to await all previous pools with `join()` before altering the shared consumer
    /// // behavior.
    /// ```
    pub fn oneshot(&self, item: Arg) -> JobHandle {
        let job_counter = Arc::new((Mutex::new(0), Condvar::new()));

        let oneshot_thread = {
            let pool = self.consumer_pool.clone();
            let job_counter = Arc::clone(&job_counter);
            let tx = self.tx.clone();
            thread::spawn(move || {
                let job_counter = JobCounter::new(job_counter);
                pool.execute(move || {
                    let job = Job(item, job_counter);
                    tx.send(job).unwrap();
                });
            })
        };

        JobHandle::new(oneshot_thread, job_counter)
    }

    /// Waits for all tasks to finish their work and return the shared resource afterwards.
    ///
    /// This implicitly waits for all created pools to be finished, since their jobs all end up in
    /// the shared consumer. Note that after this call, this pool builder can no longer be used,
    /// since the shared resource will be moved to the caller.
    ///
    /// This method returns a [`thread::Result`]. Since the `Err` variant of this specialized
    /// `Result` does not implement the [`Error`](std::error::Error) trait, the `?`-operator does
    /// not work here. For more information about how to handle panics in this case, please refer
    /// to the documentation of [`thread::Result`].
    ///
    /// # Example:
    ///
    /// ```rust
    /// # use shared_resource_pool_builder::SharedResourcePoolBuilder;
    /// #
    /// # fn shared_consumer_fn(vec: &mut Vec<i32>, i: i32) {};
    /// # fn heavy_algorithm(i: i32) -> i32 { i }
    /// #
    /// # fn example() {
    /// let pool_builder = SharedResourcePoolBuilder::new(Vec::new(), shared_consumer_fn);
    /// pool_builder.create_pool(
    ///     |tx| (0..10).for_each(|i| tx.send(i).unwrap()),
    ///     |i| heavy_algorithm(i),
    /// );
    ///
    /// let result = pool_builder.join().unwrap();
    /// # }
    /// ```
    pub fn join(self) -> thread::Result<SR> {
        drop(self.tx);
        self.handler_thread.join()
    }
}

impl<Arg, SR> SharedResourcePoolBuilder<Sender<Job<Arg>>, SR>
where
    Arg: Send + 'static,
    SR: Send + 'static,
{
    /// Creates a new unbounded pool builder.
    ///
    /// This function takes two parameters:
    ///
    /// -   The shared resource
    ///
    ///     This will be the resource that is used with every item that gets sent from the pool
    ///     consumer functions. Usually this will be something that cannot be easily shared with
    ///     multiple threads, like a database connection object. But this is not a restriction, you
    ///     can use pretty much everything as the shared resource.
    ///
    /// -   The shared consumer function
    ///
    ///     This function is called for each item that comes from the pool consumers, together with
    ///     the shared resource. To give you the maximum flexibility, the function must take two
    ///     parameters: The shared resource and an item. The type of the item will be always the
    ///     same for every pool consumer you create with this builder.
    ///
    /// Note, that the message channel, which is used by the pool consumers to communicate with the
    /// shared consumer, is unlimited (in other words, it uses [`channel()`]). On modern systems
    /// and "typical" use-cases, this should not be a problem. If however your system is low on
    /// memory or your producers generate millions over millions of items, then you might be
    /// interested in the [bounded](`Self::new_bounded()`) variant of this method.
    ///
    /// # Example
    ///
    /// ```rust
    /// # use shared_resource_pool_builder::SharedResourcePoolBuilder;
    /// #
    /// let pool_builder = SharedResourcePoolBuilder::new(
    ///     // We can use pretty much anything as the shared resource. Here, we are using a Vector:
    ///     Vec::new(),
    ///
    ///     // Naturally, our shared consumer will add an item to the Vector. The type of "i" can
    ///     // either be given explicitly, or simply let Rust infer it.
    ///     |vec, i| vec.push(i)
    /// );
    ///
    /// // Now we create a (very simple) pool for demonstration purpose. Since we return "i"
    /// // unaltered, the parameter type of the shared consumer as well as the item type of the
    /// // shared Vector will be inferred to "u8".
    /// pool_builder.create_pool(
    ///     |tx| tx.send(1u8).unwrap(),
    ///     |i| i,
    /// );
    /// ```
    pub fn new<SC>(shared_resource: SR, shared_consumer_fn: SC) -> Self
    where
        SC: FnMut(&mut SR, Arg) -> () + Send + Sync + 'static,
    {
        let (tx, rx) = channel();
        Self::init(tx, rx, shared_resource, shared_consumer_fn)
    }
}

impl<Arg, SR> SharedResourcePoolBuilder<SyncSender<Job<Arg>>, SR>
where
    Arg: Send + 'static,
    SR: Send + 'static,
{
    /// Creates a new bounded pool builder.
    ///
    /// This method is nearly identical to its [unbounded](`Self::new()`) variant. For a detailled
    /// description of the shared resource and shared consumer parameters, please look there.
    ///
    /// The difference is, that this function takes an additional integer parameter, which limits
    /// the size of the message channel, that is used by the pool consumers to communicate with the
    /// shared consumer (in other words, it uses [`sync_channel()`]). If the channel is full, the
    /// pool consumers will block until the shared consumer takes at least one item. This can be
    /// useful if you expect a huge amount of items to be generated, or if your system is low on
    /// memory.
    ///
    /// # Example
    ///
    /// ```rust
    /// # use shared_resource_pool_builder::SharedResourcePoolBuilder;
    /// #
    /// let pool_builder = SharedResourcePoolBuilder::new_bounded(
    ///     // We are very low on memory
    ///     10,
    ///
    ///     // We can use pretty much anything as the shared resource. Here, we are using a Vector:
    ///     Vec::new(),
    ///
    ///     // Naturally, our shared consumer will add an item to the Vector. The type of "i" can
    ///     // either be given explicitly, or simply let Rust infer it.
    ///     |vec, i| vec.push(i)
    /// );
    ///
    /// // Now we create a (very simple) pool for demonstration purpose. Since we return "i"
    /// // unaltered, the parameter type of the shared consumer as well as the item type of the
    /// // shared Vector will be inferred to "u8".
    /// pool_builder.create_pool(
    ///     |tx| tx.send(1u8).unwrap(),
    ///     |i| i,
    /// );
    ///
    /// // No matter how many pools we create, the maximum buffered items will never exceed 10.
    /// ```
    pub fn new_bounded<SC>(bound: usize, shared_resource: SR, shared_consumer_fn: SC) -> Self
    where
        SC: FnMut(&mut SR, Arg) -> () + Send + Sync + 'static,
    {
        let (tx, rx) = sync_channel(bound);
        Self::init(tx, rx, shared_resource, shared_consumer_fn)
    }
}

#[cfg(test)]
mod tests {
    use std::time::{Duration, Instant};

    use super::*;

    struct TestResource(Vec<TestElem>);

    impl TestResource {
        fn add(&mut self, elem: TestElem) {
            self.0.push(elem);
        }
    }

    struct TestElem(String);

    #[test]
    fn test_one_integer() {
        let consumer_fn = |i| i * 10;

        let pool_builder = SharedResourcePoolBuilder::new(Vec::new(), |vec, i| vec.push(i));
        pool_builder.create_pool(
            |tx| vec![1].into_iter().for_each(|i| tx.send(i).unwrap()),
            consumer_fn,
        );

        let result = {
            let mut result = pool_builder.join().unwrap();
            result.sort();
            result
        };

        assert_eq!(result, vec![10]);
    }

    #[test]
    fn test_few_integers() {
        let consumer_fn = |i| i * 10;

        let pool_builder = SharedResourcePoolBuilder::new(Vec::new(), |vec, i| vec.push(i));
        pool_builder.create_pool(|tx| (0..5).for_each(|i| tx.send(i).unwrap()), consumer_fn);

        let result = {
            let mut result = pool_builder.join().unwrap();
            result.sort();
            result
        };

        assert_eq!(result, (0..5).map(consumer_fn).collect::<Vec<_>>());
    }

    #[test]
    fn test_few_integers_with_oneshot() {
        let consumer_fn = |i| i * 10;

        let pool_builder = SharedResourcePoolBuilder::new(Vec::new(), |vec, i| vec.push(i));
        pool_builder.create_pool(|tx| (0..5).for_each(|i| tx.send(i).unwrap()), consumer_fn);
        pool_builder.oneshot(consumer_fn(5));

        let result = {
            let mut result = pool_builder.join().unwrap();
            result.sort();
            result
        };

        assert_eq!(result, (0..6).map(consumer_fn).collect::<Vec<_>>());
    }

    #[test]
    fn test_few_integers_with_delayed_producer() {
        let consumer_fn = |i| i * 10;

        let pool_builder = SharedResourcePoolBuilder::new(Vec::new(), |vec, i| vec.push(i));
        pool_builder.create_pool(
            |tx| {
                thread::sleep(Duration::from_millis(10));
                (0..5).for_each(|i| tx.send(i).unwrap());
            },
            consumer_fn,
        );

        let result = {
            let mut result = pool_builder.join().unwrap();
            result.sort();
            result
        };

        assert_eq!(result, (0..5).map(consumer_fn).collect::<Vec<_>>());
    }

    #[test]
    fn test_many_integers_with_bounded_shared_producer() {
        let consumer_fn = |i| i * 10;

        let pool_builder =
            SharedResourcePoolBuilder::new_bounded(10, Vec::new(), |vec, i| vec.push(i));
        pool_builder.create_pool(
            |tx| (0..1000).for_each(|i| tx.send(i).unwrap()),
            consumer_fn,
        );

        let result = {
            let mut result = pool_builder.join().unwrap();
            result.sort();
            result
        };

        assert_eq!(result, (0..1000).map(consumer_fn).collect::<Vec<_>>());
    }

    #[test]
    fn test_many_integers_with_bounded_item_producer() {
        let consumer_fn = |i| i * 10;

        let pool_builder = SharedResourcePoolBuilder::new(Vec::new(), |vec, i| vec.push(i));
        pool_builder.create_pool_bounded(
            10,
            |tx| (0..1000).for_each(|i| tx.send(i).unwrap()),
            consumer_fn,
        );

        let result = {
            let mut result = pool_builder.join().unwrap();
            result.sort();
            result
        };

        assert_eq!(result, (0..1000).map(consumer_fn).collect::<Vec<_>>());
    }

    #[test]
    fn test_many_integers_with_bounded_shared_and_item_producer() {
        let consumer_fn = |i| i * 10;

        let pool_builder =
            SharedResourcePoolBuilder::new_bounded(10, Vec::new(), |vec, i| vec.push(i));
        pool_builder.create_pool_bounded(
            10,
            |tx| (0..1000).for_each(|i| tx.send(i).unwrap()),
            consumer_fn,
        );

        let result = {
            let mut result = pool_builder.join().unwrap();
            result.sort();
            result
        };

        assert_eq!(result, (0..1000).map(consumer_fn).collect::<Vec<_>>());
    }

    #[test]
    fn test_many_integers() {
        let consumer_fn = |i| i * 10;

        let pool_builder = SharedResourcePoolBuilder::new(Vec::new(), |vec, i| vec.push(i));
        pool_builder.create_pool(
            |tx| (0..1000).for_each(|i| tx.send(i).unwrap()),
            consumer_fn,
        );

        let result = {
            let mut result = pool_builder.join().unwrap();
            result.sort();
            result
        };

        assert_eq!(result, (0..1000).map(consumer_fn).collect::<Vec<_>>());
    }

    #[test]
    fn test_wait_until_pool_finishes() {
        let consumer_fn = |i| i * 10;

        let pool_builder = SharedResourcePoolBuilder::new(Vec::new(), |vec, i| vec.push(i));
        let pool = pool_builder.create_pool(
            |tx| tx.send(1).unwrap(),
            move |parg| {
                thread::sleep(Duration::from_millis(10));
                consumer_fn(parg)
            },
        );

        pool.join().unwrap();

        let now = Instant::now();

        let result = {
            let mut result = pool_builder.join().unwrap();
            result.sort();
            result
        };

        let millis = now.elapsed().as_millis();
        assert!(millis < 10);

        assert_eq!(result, vec![10]);
    }

    #[test]
    fn test_integers_multiple_pools_parallel() {
        let pool_builder = SharedResourcePoolBuilder::new(Vec::new(), |vec, i| vec.push(i));
        let pools = vec![
            pool_builder.create_pool(|tx| (0..2).for_each(|i| tx.send(i).unwrap()), |i| i * 10),
            pool_builder.create_pool(|tx| (2..5).for_each(|i| tx.send(i).unwrap()), |i| i * 10),
        ];

        for pool in pools {
            pool.join().unwrap();
        }

        let result = {
            let mut result = pool_builder.join().unwrap();
            result.sort();
            result
        };

        assert_eq!(result, vec![0, 10, 20, 30, 40])
    }

    #[test]
    fn test_integers_multiple_pools_sequential() {
        let pool_builder = SharedResourcePoolBuilder::new(Vec::new(), |vec, i| vec.push(i));

        let pool =
            pool_builder.create_pool(|tx| (2..5).for_each(|i| tx.send(i).unwrap()), |i| i * 10);

        pool.join().unwrap();

        let pool =
            pool_builder.create_pool(|tx| (0..2).for_each(|i| tx.send(i).unwrap()), |i| i * 10);

        pool.join().unwrap();

        let result = {
            let mut result = pool_builder.join().unwrap();
            result.sort();
            result
        };

        assert_eq!(result, vec![0, 10, 20, 30, 40])
    }

    #[test]
    fn test_integers_multiple_pools_with_parallel_producers() {
        let producer_pool = threadpool::Builder::new().build();

        let pool_builder = SharedResourcePoolBuilder::new(Vec::new(), |vec, i| vec.push(i));
        let pools = vec![
            {
                let producer_pool = producer_pool.clone();
                pool_builder.create_pool(
                    move |tx| {
                        (0..50).into_iter().for_each(|i| {
                            let tx = tx.clone();
                            producer_pool.execute(move || tx.send(i).unwrap())
                        });
                    },
                    |i| i * 10,
                )
            },
            {
                let producer_pool = producer_pool.clone();
                pool_builder.create_pool(
                    move |tx| {
                        (50..100).into_iter().for_each(|i| {
                            let tx = tx.clone();
                            producer_pool.execute(move || tx.send(i).unwrap())
                        });
                    },
                    |i| i * 10,
                )
            },
        ];

        for pool in pools {
            pool.join().unwrap();
        }

        let result = {
            let mut result = pool_builder.join().unwrap();
            result.sort();
            result
        };

        assert_eq!(
            result,
            (0..100).into_iter().map(|i| i * 10).collect::<Vec<_>>()
        )
    }

    #[test]
    fn test_custom_types() {
        let producer_fn = || ('a'..='z').map(|c| String::from(c));

        let pool_builder =
            SharedResourcePoolBuilder::new(TestResource(Vec::new()), |tres, e| tres.add(e));
        pool_builder.create_pool(
            move |tx| producer_fn().for_each(|i| tx.send(i).unwrap()),
            |c| TestElem(c),
        );

        let result = {
            let mut result = pool_builder
                .join()
                .unwrap()
                .0
                .iter()
                .map(|e| e.0.clone())
                .collect::<Vec<_>>();
            result.sort();
            result
        };

        assert_eq!(result, producer_fn().collect::<Vec<_>>());
    }
}