1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! The "green scheduling" library
13 //! This library provides M:N threading for rust programs. Internally this has
14 //! the implementation of a green scheduler along with context switching and a
15 //! stack-allocation strategy. This can be optionally linked in to rust
16 //! programs in order to provide M:N functionality inside of 1:1 programs.
20 //! An M:N scheduling library implies that there are N OS thread upon which M
21 //! "green threads" are multiplexed. In other words, a set of green threads are
22 //! all run inside a pool of OS threads.
24 //! With this design, you can achieve _concurrency_ by spawning many green
25 //! threads, and you can achieve _parallelism_ by running the green threads
26 //! simultaneously on multiple OS threads. Each OS thread is a candidate for
27 //! being scheduled on a different core (the source of parallelism), and then
28 //! all of the green threads cooperatively schedule amongst one another (the
29 //! source of concurrency).
33 //! In order to coordinate among green threads, each OS thread is primarily
34 //! running something which we call a Scheduler. Whenever a reference to a
35 //! Scheduler is made, it is synonymous to referencing one OS thread. Each
36 //! scheduler is bound to one and exactly one OS thread, and the thread that it
37 //! is bound to never changes.
39 //! Each scheduler is connected to a pool of other schedulers (a `SchedPool`)
40 //! which is the thread pool term from above. A pool of schedulers all share the
41 //! work that they create. Furthermore, whenever a green thread is created (also
42 //! synonymously referred to as a green task), it is associated with a
43 //! `SchedPool` forevermore. A green thread cannot leave its scheduler pool.
45 //! Schedulers can have at most one green thread running on them at a time. When
46 //! a scheduler is asleep on its event loop, there are no green tasks running on
47 //! the OS thread or the scheduler. The term "context switch" is used for when
48 //! the running green thread is swapped out, but this simply changes the one
49 //! green thread which is running on the scheduler.
53 //! A green thread can largely be summarized by a stack and a register context.
54 //! Whenever a green thread is spawned, it allocates a stack, and then prepares
55 //! a register context for execution. The green task may be executed across
56 //! multiple OS threads, but it will always use the same stack and it will carry
57 //! its register context across OS threads.
59 //! Each green thread is cooperatively scheduled with other green threads.
60 //! Primarily, this means that there is no pre-emption of a green thread. The
61 //! major consequence of this design is that a green thread stuck in an infinite
62 //! loop will prevent all other green threads from running on that particular
65 //! Scheduling events for green threads occur on communication and I/O
66 //! boundaries. For example, if a green task blocks waiting for a message on a
67 //! channel some other green thread can now run on the scheduler. This also has
68 //! the consequence that until a green thread performs any form of scheduling
69 //! event, it will be running on the same OS thread (unconditionally).
73 //! With a pool of schedulers, a new green task has a number of options when
74 //! deciding where to run initially. The current implementation uses a concept
75 //! called work stealing in order to spread out work among schedulers.
77 //! In a work-stealing model, each scheduler maintains a local queue of tasks to
78 //! run, and this queue is stolen from by other schedulers. Implementation-wise,
79 //! work stealing has some hairy parts, but from a user-perspective, work
80 //! stealing simply implies what with M green threads and N schedulers where
81 //! M > N it is very likely that all schedulers will be busy executing work.
83 //! # Considerations when using libgreen
85 //! An M:N runtime has both pros and cons, and there is no one answer as to
86 //! whether M:N or 1:1 is appropriate to use. As always, there are many
87 //! advantages and disadvantages between the two. Regardless of the workload,
88 //! however, there are some aspects of using green thread which you should be
91 //! * The largest concern when using libgreen is interoperating with native
92 //! code. Care should be taken when calling native code that will block the OS
93 //! thread as it will prevent further green tasks from being scheduled on the
96 //! * Native code using thread-local-storage should be approached
97 //! with care. Green threads may migrate among OS threads at any time, so
98 //! native libraries using thread-local state may not always work.
100 //! * Native synchronization primitives (e.g. pthread mutexes) will also not
101 //! work for green threads. The reason for this is because native primitives
102 //! often operate on a _os thread_ granularity whereas green threads are
103 //! operating on a more granular unit of work.
105 //! * A green threading runtime is not fork-safe. If the process forks(), it
106 //! cannot expect to make reasonable progress by continuing to use green
109 //! Note that these concerns do not mean that operating with native code is a
110 //! lost cause. These are simply just concerns which should be considered when
111 //! invoking native code.
113 //! # Starting with libgreen
116 //! extern crate green;
119 //! fn start(argc: int, argv: *const *const u8) -> int {
120 //! green::start(argc, argv, green::basic::event_loop, main)
124 //! // this code is running in a pool of schedulers
128 //! > **Note**: This `main` function in this example does *not* have I/O
129 //! > support. The basic event loop does not provide any support
131 //! # Starting with I/O support in libgreen
134 //! extern crate green;
135 //! extern crate rustuv;
138 //! fn start(argc: int, argv: *const *const u8) -> int {
139 //! green::start(argc, argv, rustuv::event_loop, main)
143 //! // this code is running in a pool of schedulers all powered by libuv
147 //! The above code can also be shortened with a macro from libgreen.
150 //! #![feature(phase)]
151 //! #[phase(plugin)] extern crate green;
153 //! green_start!(main)
156 //! // run inside of a green pool
160 //! # Using a scheduler pool
162 //! This library adds a `GreenTaskBuilder` trait that extends the methods
163 //! available on `std::task::TaskBuilder` to allow spawning a green task,
164 //! possibly pinned to a particular scheduler thread:
167 //! extern crate green;
168 //! extern crate rustuv;
171 //! use std::task::TaskBuilder;
172 //! use green::{SchedPool, PoolConfig, GreenTaskBuilder};
174 //! let mut config = PoolConfig::new();
176 //! // Optional: Set the event loop to be rustuv's to allow I/O to work
177 //! config.event_loop_factory = rustuv::event_loop;
179 //! let mut pool = SchedPool::new(config);
181 //! // Spawn tasks into the pool of schedulers
182 //! TaskBuilder::new().green(&mut pool).spawn(proc() {
183 //! // this code is running inside the pool of schedulers
186 //! // this code is also running inside the same scheduler pool
190 //! // Dynamically add a new scheduler to the scheduler pool. This adds another
191 //! // OS thread that green threads can be multiplexed on to.
192 //! let mut handle = pool.spawn_sched();
194 //! // Pin a task to the spawned scheduler
195 //! TaskBuilder::new().green_pinned(&mut pool, &mut handle).spawn(proc() {
199 //! // Handles keep schedulers alive, so be sure to drop all handles before
200 //! // destroying the sched pool
203 //! // Required to shut down this scheduler pool.
204 //! // The task will fail if `shutdown` is not called.
209 #![crate_name = "green"]
211 #![license = "MIT/ASL2"]
212 #![crate_type = "rlib"]
213 #![crate_type = "dylib"]
214 #![doc(html_logo_url = "http://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
215 html_favicon_url = "http://www.rust-lang.org/favicon.ico",
216 html_root_url = "http://doc.rust-lang.org/master/",
217 html_playground_url = "http://play.rust-lang.org/")]
219 // NB this does *not* include globs, please keep it that way.
220 #![feature(macro_rules, phase, default_type_params)]
221 #![allow(visible_private_types, deprecated)]
223 #[cfg(test)] #[phase(plugin, link)] extern crate log;
224 #[cfg(test)] extern crate rustuv;
229 use std::mem::replace;
232 use std::rt::thread::Thread;
233 use std::rt::task::TaskOpts;
235 use std::sync::atomics::{SeqCst, AtomicUint, INIT_ATOMIC_UINT};
236 use std::sync::deque;
237 use std::task::{TaskBuilder, Spawner};
239 use sched::{Shutdown, Scheduler, SchedHandle, TaskFromFriend, PinnedTask, NewNeighbor};
240 use sleeper_list::SleeperList;
241 use stack::StackPool;
252 pub mod sleeper_list;
256 /// A helper macro for booting a program with libgreen
261 /// #![feature(phase)]
262 /// #[phase(plugin)] extern crate green;
264 /// green_start!(main)
267 /// // running with libgreen
271 macro_rules! green_start( ($f:ident) => (
277 fn start(argc: int, argv: *const *const u8) -> int {
278 green::start(argc, argv, rustuv::event_loop, super::$f)
283 /// Set up a default runtime configuration, given compiler-supplied arguments.
285 /// This function will block until the entire pool of M:N schedulers have
286 /// exited. This function also requires a local task to be available.
290 /// * `argc` & `argv` - The argument vector. On Unix this information is used
292 /// * `main` - The initial procedure to run inside of the M:N scheduling pool.
293 /// Once this procedure exits, the scheduling pool will begin to shut
294 /// down. The entire pool (and this function) will only return once
295 /// all child tasks have finished executing.
299 /// The return value is used as the process return code. 0 on success, 101 on
301 pub fn start(argc: int, argv: *const *const u8,
302 event_loop_factory: fn() -> Box<rtio::EventLoop + Send>,
303 main: proc():Send) -> int {
304 rt::init(argc, argv);
305 let mut main = Some(main);
307 simple::task().run(|| {
308 ret = Some(run(event_loop_factory, main.take_unwrap()));
310 // unsafe is ok b/c we're sure that the runtime is gone
311 unsafe { rt::cleanup() }
315 /// Execute the main function in a pool of M:N schedulers.
317 /// Configures the runtime according to the environment, by default using a task
318 /// scheduler with the same number of threads as cores. Returns a process exit
321 /// This function will not return until all schedulers in the associated pool
323 pub fn run(event_loop_factory: fn() -> Box<rtio::EventLoop + Send>,
324 main: proc():Send) -> int {
325 // Create a scheduler pool and spawn the main task into this pool. We will
326 // get notified over a channel when the main task exits.
327 let mut cfg = PoolConfig::new();
328 cfg.event_loop_factory = event_loop_factory;
329 let mut pool = SchedPool::new(cfg);
330 let (tx, rx) = channel();
331 let mut opts = TaskOpts::new();
332 opts.on_exit = Some(proc(r) tx.send(r));
333 opts.name = Some("<main>".into_maybe_owned());
334 pool.spawn(opts, main);
336 // Wait for the main task to return, and set the process error code
338 if rx.recv().is_err() {
339 os::set_exit_status(rt::DEFAULT_ERROR_CODE);
342 // Now that we're sure all tasks are dead, shut down the pool of schedulers,
343 // waiting for them all to return.
345 os::get_exit_status()
348 /// Configuration of how an M:N pool of schedulers is spawned.
349 pub struct PoolConfig {
350 /// The number of schedulers (OS threads) to spawn into this M:N pool.
352 /// A factory function used to create new event loops. If this is not
353 /// specified then the default event loop factory is used.
354 pub event_loop_factory: fn() -> Box<rtio::EventLoop + Send>,
358 /// Returns the default configuration, as determined the environment
359 /// variables of this process.
360 pub fn new() -> PoolConfig {
362 threads: rt::default_sched_threads(),
363 event_loop_factory: basic::event_loop,
368 /// A structure representing a handle to a pool of schedulers. This handle is
369 /// used to keep the pool alive and also reap the status from the pool.
370 pub struct SchedPool {
372 threads: Vec<Thread<()>>,
373 handles: Vec<SchedHandle>,
374 stealers: Vec<deque::Stealer<Box<task::GreenTask>>>,
376 stack_pool: StackPool,
377 deque_pool: deque::BufferPool<Box<task::GreenTask>>,
378 sleepers: SleeperList,
379 factory: fn() -> Box<rtio::EventLoop + Send>,
380 task_state: TaskState,
381 tasks_done: Receiver<()>,
384 /// This is an internal state shared among a pool of schedulers. This is used to
385 /// keep track of how many tasks are currently running in the pool and then
386 /// sending on a channel once the entire pool has been drained of all tasks.
389 cnt: Arc<AtomicUint>,
394 /// Execute the main function in a pool of M:N schedulers.
396 /// This will configure the pool according to the `config` parameter, and
397 /// initially run `main` inside the pool of schedulers.
398 pub fn new(config: PoolConfig) -> SchedPool {
399 static mut POOL_ID: AtomicUint = INIT_ATOMIC_UINT;
403 event_loop_factory: factory
405 assert!(nscheds > 0);
407 // The pool of schedulers that will be returned from this function
408 let (p, state) = TaskState::new();
409 let mut pool = SchedPool {
413 id: unsafe { POOL_ID.fetch_add(1, SeqCst) },
414 sleepers: SleeperList::new(),
415 stack_pool: StackPool::new(),
416 deque_pool: deque::BufferPool::new(),
423 // Create a work queue for each scheduler, ntimes. Create an extra
424 // for the main thread if that flag is set. We won't steal from it.
425 let mut workers = Vec::with_capacity(nscheds);
426 let mut stealers = Vec::with_capacity(nscheds);
428 for _ in range(0, nscheds) {
429 let (w, s) = pool.deque_pool.deque();
433 pool.stealers = stealers;
435 // Now that we've got all our work queues, create one scheduler per
436 // queue, spawn the scheduler into a thread, and be sure to keep a
437 // handle to the scheduler and the thread to keep them alive.
438 for worker in workers.move_iter() {
439 rtdebug!("inserting a regular scheduler");
441 let mut sched = box Scheduler::new(pool.id,
444 pool.stealers.clone(),
445 pool.sleepers.clone(),
446 pool.task_state.clone());
447 pool.handles.push(sched.make_handle());
448 pool.threads.push(Thread::start(proc() { sched.bootstrap(); }));
454 /// Creates a new task configured to run inside of this pool of schedulers.
455 /// This is useful to create a task which can then be sent to a specific
456 /// scheduler created by `spawn_sched` (and possibly pin it to that
458 #[deprecated = "use the green and green_pinned methods of GreenTaskBuilder instead"]
459 pub fn task(&mut self, opts: TaskOpts, f: proc():Send) -> Box<GreenTask> {
460 GreenTask::configure(&mut self.stack_pool, opts, f)
463 /// Spawns a new task into this pool of schedulers, using the specified
464 /// options to configure the new task which is spawned.
466 /// New tasks are spawned in a round-robin fashion to the schedulers in this
467 /// pool, but tasks can certainly migrate among schedulers once they're in
469 #[deprecated = "use the green and green_pinned methods of GreenTaskBuilder instead"]
470 pub fn spawn(&mut self, opts: TaskOpts, f: proc():Send) {
471 let task = self.task(opts, f);
473 // Figure out someone to send this task to
474 let idx = self.next_friend;
475 self.next_friend += 1;
476 if self.next_friend >= self.handles.len() {
477 self.next_friend = 0;
480 // Jettison the task away!
481 self.handles.get_mut(idx).send(TaskFromFriend(task));
484 /// Spawns a new scheduler into this M:N pool. A handle is returned to the
485 /// scheduler for use. The scheduler will not exit as long as this handle is
488 /// The scheduler spawned will participate in work stealing with all of the
489 /// other schedulers currently in the scheduler pool.
490 pub fn spawn_sched(&mut self) -> SchedHandle {
491 let (worker, stealer) = self.deque_pool.deque();
492 self.stealers.push(stealer.clone());
494 // Tell all existing schedulers about this new scheduler so they can all
495 // steal work from it
496 for handle in self.handles.mut_iter() {
497 handle.send(NewNeighbor(stealer.clone()));
500 // Create the new scheduler, using the same sleeper list as all the
501 // other schedulers as well as having a stealer handle to all other
503 let mut sched = box Scheduler::new(self.id,
506 self.stealers.clone(),
507 self.sleepers.clone(),
508 self.task_state.clone());
509 let ret = sched.make_handle();
510 self.handles.push(sched.make_handle());
511 self.threads.push(Thread::start(proc() { sched.bootstrap() }));
516 /// Consumes the pool of schedulers, waiting for all tasks to exit and all
517 /// schedulers to shut down.
519 /// This function is required to be called in order to drop a pool of
520 /// schedulers, it is considered an error to drop a pool without calling
523 /// This only waits for all tasks in *this pool* of schedulers to exit, any
524 /// native tasks or extern pools will not be waited on
525 pub fn shutdown(mut self) {
526 self.stealers = vec![];
528 // Wait for everyone to exit. We may have reached a 0-task count
529 // multiple times in the past, meaning there could be several buffered
530 // messages on the `tasks_done` port. We're guaranteed that after *some*
531 // message the current task count will be 0, so we just receive in a
532 // loop until everything is totally dead.
533 while self.task_state.active() {
534 self.tasks_done.recv();
537 // Now that everyone's gone, tell everything to shut down.
538 for mut handle in replace(&mut self.handles, vec![]).move_iter() {
539 handle.send(Shutdown);
541 for thread in replace(&mut self.threads, vec![]).move_iter() {
548 fn new() -> (Receiver<()>, TaskState) {
549 let (tx, rx) = channel();
551 cnt: Arc::new(AtomicUint::new(0)),
556 fn increment(&mut self) {
557 self.cnt.fetch_add(1, SeqCst);
560 fn active(&self) -> bool {
561 self.cnt.load(SeqCst) != 0
564 fn decrement(&mut self) {
565 let prev = self.cnt.fetch_sub(1, SeqCst);
572 impl Drop for SchedPool {
574 if self.threads.len() > 0 {
575 fail!("dropping a M:N scheduler pool that wasn't shut down");
580 /// A spawner for green tasks
581 pub struct GreenSpawner<'a>{
582 pool: &'a mut SchedPool,
583 handle: Option<&'a mut SchedHandle>
586 impl<'a> Spawner for GreenSpawner<'a> {
588 fn spawn(self, opts: TaskOpts, f: proc():Send) {
589 let GreenSpawner { pool, handle } = self;
591 None => pool.spawn(opts, f),
592 Some(h) => h.send(PinnedTask(pool.task(opts, f)))
597 /// An extension trait adding `green` configuration methods to `TaskBuilder`.
598 pub trait GreenTaskBuilder {
599 fn green<'a>(self, &'a mut SchedPool) -> TaskBuilder<GreenSpawner<'a>>;
600 fn green_pinned<'a>(self, &'a mut SchedPool, &'a mut SchedHandle)
601 -> TaskBuilder<GreenSpawner<'a>>;
604 impl<S: Spawner> GreenTaskBuilder for TaskBuilder<S> {
605 fn green<'a>(self, pool: &'a mut SchedPool) -> TaskBuilder<GreenSpawner<'a>> {
606 self.spawner(GreenSpawner {pool: pool, handle: None})
609 fn green_pinned<'a>(self, pool: &'a mut SchedPool, handle: &'a mut SchedHandle)
610 -> TaskBuilder<GreenSpawner<'a>> {
611 self.spawner(GreenSpawner {pool: pool, handle: Some(handle)})
617 use std::task::TaskBuilder;
618 use super::{SchedPool, PoolConfig, GreenTaskBuilder};
621 fn test_green_builder() {
622 let mut pool = SchedPool::new(PoolConfig::new());
623 let res = TaskBuilder::new().green(&mut pool).try(proc() {
624 "Success!".to_string()
626 assert_eq!(res.ok().unwrap(), "Success!".to_string());