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//! Dynpool is a thread manager that is lightweight, flexible, and rescalable. //! The pool is designed for minimal overhead, without expensive locks or an //! extra management thread. Add a job queue yourself, or don't! //! //! To use dynpool, all you need is an implementation of `System`. The pool will //! repeatedly call `System::work` from many threads, each with a per-thread //! data object. Rather than requiring you to rescale the pool from the outside, //! `dynpool` will constantly query the worker count from `System::scale`. This //! is actually faster, since a simple `scale` implementation can be inlined //! into the worker! Your system can be run in the background, and controlled //! through the `Pool` object, or run in the foreground to make use of the //! current thread. //! //! ``` //! # extern crate dynpool; //! # use dynpool::*; //! # use std::thread::sleep; //! # use std::time::{Duration, Instant}; //! struct Printer(Instant); //! //! impl System for Printer { //! type Data = String; //! //! // How many threads? The pool will scale up over time! //! fn scale(&self) -> Scale { //! let time = self.0.elapsed(); //! let ms = time.as_secs() * 1000 + time.subsec_millis() as u64; //! match ms { //! 0..=200 => Scale::active(1), //! 201..=400 => Scale::active(2), //! 401..=600 => Scale::active(3), //! 601..=800 => Scale::active(4), //! _ => Scale::shutdown(), //! } //! } //! //! // Pick a string for each thread. //! fn init(&self, index: usize) -> String { //! match index { //! 0 => "Hello", //! 1 => "Hola", //! 2 => "Bonjour", //! 3 => "Ciao", //! _ => unreachable!(), //! }.to_owned() //! } //! //! // Do work on several threads! //! fn work(&self, text: &mut String) -> Decision { //! println!("{}", text); //! *text += " Again"; //! sleep(Duration::from_millis(100)); //! Decision::Again //! } //! } //! //! fn main() { //! Pool::start_fg(Printer(Instant::now())).unwrap(); //! println!("This is the end!"); //! } //! ``` //! //! There are also builtin functions for concisely altering and constructing systems. //! //! ``` //! # extern crate dynpool; //! # use dynpool::*; //! # use std::thread::sleep; //! # use std::time::{Duration, Instant}; //! # fn main() { //! let workers = func_worker(|index| { //! println!("New worker #{}", index); //! move || { //! println!("Hello from #{}", index); //! Decision::Again //! } //! }); //! let sys = with_threads(workers, 10); //! let end_time = Instant::now() + Duration::from_millis(500); //! Pool::start_fg(shutdown_after(sys, end_time)).unwrap(); //! # } //! ``` #![cfg_attr(feature = "nightly", feature(atomic_min_max))] #![deny(bare_trait_objects)] #![warn(missing_docs)] pub(crate) mod util; pub(crate) mod internal; mod builtins; pub use builtins::*; use std::fmt; use std::error::Error as StdError; use std::sync::Arc; use internal::{SysRunner, PoolData, CountState}; /// A handle to a lightweight thread pool. This is the primary type in the /// dynpool crate. /// /// Pools spawn and close threads in LIFO (last spawned is first destroyed) /// order. A worker (the context of execution bound to each thread) can be /// restarted by issuing a `Restart` decision, but the thread itself will only /// shutdown if the scale is decreased. pub struct Pool<X> { /// the polymorphic pool data and work dispatcher data: Arc<PoolData>, /// a monomorphic view of the work dispatcher run: Arc<SysRunner<X>>, } impl<X: System> Pool<X> { /// Create a new manager without running anything. pub(crate) fn new(sys: X) -> Pool<X> { let run = Arc::new(SysRunner { sys, epoc: 0, }); Pool { data: PoolData::new(run.clone()), run, } } /// Create a new manager which runs the given system in the background, /// starting a new thread for each worker. pub fn start_bg(sys: X) -> Pool<X> { let share = Pool::new(sys); internal::start(share.data.clone(), 0 /* index */); share } /// Create a new manager which runs the given system in the foreground, /// using the current thread to host the first worker. It will return when /// all workers have shutdown. /// /// If a worker panics with unwind, then this function will return /// `Err(PoolPanicedError)` instantly, even if some workers are still /// completing work. Due to limitations in `std`, It is undefined behavior /// for a worker to panic with abort. pub fn start_fg(sys: X) -> Result<(), PoolPanicedError> { let share = Pool::new(sys); internal::bootstrap(share.data.clone(), 0 /* index */); if share.has_paniced() { Err(PoolPanicedError) } else { Ok(()) } } /// Gracefully change the system that this pool executes, and slowly replace /// all workers. This does not destroy the system or this handle. It simply /// tells threads to work on new tasks. A new pool handle is returned. pub fn swap_system<Y: System>(&self, sys: Y) -> Pool<Y> { let mut w = self.data.runner.write().unwrap(); let epoc = self.data.next_epoc(); let runner = Arc::new(SysRunner::new(sys, epoc)); *w = runner.clone(); Pool { data: self.data.clone(), run: runner, } } /// Get a reference to the system associated with this pool handle. This /// system is *not* necessarily receiving work, since a different system /// may have been swapped onto the pool. pub fn system(&self) -> &X { &self.run.sys } /// Number of running threads. Note that since threads can spawn and close /// at any time as a result of queries to `System::scale`, this count may /// not be correct. pub fn thread_count(&self) -> usize { match self.data.count_state() { CountState::Running(n) => n, _ => 0, } } /// Has a worker in this pool paniced with unwind? pub fn has_paniced(&self) -> bool { match self.data.count_state() { CountState::Panic => true, _ => false, } } /// Block until all workers have shutdown. /// /// If a worker panics with unwind, then this function will return /// `Err(PoolPanicedError)` instantly, even if some workers are still /// completing work. Due to limitations in `std`, It is undefined behavior /// for a worker to panic with abort. In such a case, `join` will likely /// never return. pub fn join(self) -> Result<(), PoolPanicedError> { while self.thread_count() != 0 { *self.data.onclose.wait(self.data.onclose_mutex.lock().unwrap()).unwrap(); } if self.has_paniced() { Err(PoolPanicedError) } else { Ok(()) } } } impl<X> Clone for Pool<X> { fn clone(&self) -> Pool<X> { Pool { data: self.data.clone(), run: self.run.clone(), } } } #[cfg(feature="instrument")] #[derive(Copy, Clone, Debug)] #[allow(missing_docs)] /// Internal events available under the instrument feature. pub enum InternalEvent { /// A new thread has been spawned. ThreadSpawn { index: usize }, /// A thread has shutdown. ThreadShutdown { index: usize }, /// The system has been reloaded for a thread. ThreadReboot { index: usize }, /// A worker has started looping. WorkerLoopStart { index: usize, epoc: usize }, /// A worker has been shutdown. WorkerLoopEnd { index: usize, epoc: usize }, /// A worker skipped a loop. WorkerLoopSkip { index: usize }, } /// A goal for the worker pool. This describes the scale that the pool should /// attempt to reach. #[derive(Copy, Clone, Debug)] pub enum Scale { /// Shutdown the pool. Shutdown, /// Maintain the given number of active workers. Inactive worker threads are /// shutdown. Active(usize), /// Maintain the given number of active workers, and up to the given number /// of inactive workers. Any extra inactive worker threads are shutdown. Mixed { /// Number of active workers. active: usize, /// Maximum number of inactive worker. max_inactive: usize, }, /// Maintain the given number of active workers, and an unlimited number of /// inactive workers. No worker threads will be terminated unless one /// panics. NoTerm { /// Number of active workers. active: usize, }, } impl Scale { /// Shutdown the pool. pub fn shutdown() -> Scale { Scale::Shutdown } /// Scale to exactly the given number of workers. pub fn active(num: usize) -> Scale { match num { // normalize just for kicks 0 => Scale::Shutdown, n => Scale::Active(n), } } /// Scale to the given number of active workers and no more than the given /// number of inactive workers. pub fn mixed(active: usize, max_inactive: usize) -> Scale { Scale::Mixed { active, max_inactive } } /// Scale to the given number of active workers without shutting down any /// inactive workers. pub fn no_term(active: usize) -> Scale { Scale::NoTerm { active } } /// How many active workers should the pool scale to? pub fn worker_count(self) -> usize { use self::Scale::*; match self { Shutdown => 0, Active(n) => n, Mixed { active, .. } => active, NoTerm { active } => active, } } } /// Implementors of this trait provide a function to complete work and a /// function to determine the number of worker threads. This is the primary /// trait of the dynpool crate. /// /// The user can implement this trait themselves, or use a builtin function such /// as `fixed_scale` for quick usage. pub trait System: Send + Sync + 'static { /// Per-worker data that pool should manage. Does not need to be `Sync` or /// `Send`. type Data; /// Called when a worker begins performing work, or is restarted. The /// returned data will be passed to future calls to `work`. fn init(&self, index: usize) -> Self::Data; /// Do a unit of work, and return scheduling information. fn work(&self, data: &mut Self::Data) -> Decision; /// How many active and inactive workers should the pool attempt to host? /// This function is checked frequently. It is also used to signal the /// graceful shutdown of the pool. /// /// Dynpool will behave correctly even when the scale is highly inconsistent /// between calls. However, the LIFO ordering of thread indices may be /// *momentarily* violated in such cases, due to the lack of heavy locks on /// `init` and `close`. fn scale(&self) -> Scale; /// After a worker decides to close, the associated data is passed to this /// function. Since the pool is highly parallel, and may be rapidly /// rescaling, a call to reinitialize the worker may sometimes occur before /// the call to `close` is complete. fn close(&self, Self::Data) { } #[cfg(feature="instrument")] /// Called when an internal event occurs. fn note_event(&self, _event: InternalEvent) { } } /// What should the pool do next? #[derive(Copy, Clone, Eq, PartialEq)] pub enum Decision { /// Work is incomplete. Do not stop the worker or switch to a different /// system. Poll again after some simple management checks. Incomplete, /// Poll this worker again, unless worker is stopped as part of rescaling. Again, /// Restart the worker. Restart, } /// This error singles the detection of a worker panic. #[derive(Copy, Clone, Debug)] pub struct PoolPanicedError; impl fmt::Display for PoolPanicedError { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "worker paniced in pool") } } impl StdError for PoolPanicedError { }