1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547
//! The blocking executor. //! //! Tasks created by [`Task::blocking()`] go into this executor. This executor is independent of //! [`run()`][`crate::run()`] - it does not need to be driven. //! //! Blocking tasks are allowed to block without restrictions. However, the executor puts a limit on //! the number of concurrently running tasks. Once that limit is hit, a task will need to complete //! or yield in order for others to run. //! //! In idle state, this executor has no threads and consumes no resources. Once tasks are spawned, //! new threads will get started, as many as is needed to keep up with the present amount of work. //! When threads are idle, they wait for some time for new work to come in and shut down after a //! certain timeout. //! //! This module also implements convenient adapters: //! //! - [`blocking!`] as syntax sugar around [`Task::blocking()`] //! - [`iter()`] converts an [`Iterator`] into a [`Stream`] //! - [`reader()`] converts a [`Read`] into an [`AsyncRead`] //! - [`writer()`] converts a [`Write`] into an [`AsyncWrite`] use std::collections::VecDeque; use std::future::Future; use std::io::{self, Read, Write}; use std::panic; use std::pin::Pin; use std::sync::{Condvar, Mutex, MutexGuard}; use std::task::{Context, Poll}; use std::thread; use std::time::Duration; use futures_util::io::{AllowStdIo, AsyncRead, AsyncWrite, AsyncWriteExt}; use futures_util::stream::Stream; use once_cell::sync::Lazy; use crate::context; use crate::task::{Runnable, Task}; use crate::throttle; /// The blocking executor. pub(crate) struct BlockingExecutor { /// The current state of the executor. state: Mutex<State>, /// Used to put idle threads to sleep and wake them up when new work comes in. cvar: Condvar, } /// Current state of the blocking executor. struct State { /// Number of idle threads in the pool. /// /// Idle threads are sleeping, waiting to get a task to run. idle_count: usize, /// Total number of thread in the pool. /// /// This is the number of idle threads + the number of active threads. thread_count: usize, /// The queue of blocking tasks. queue: VecDeque<Runnable>, } impl BlockingExecutor { /// Returns a reference to the blocking executor. pub fn get() -> &'static BlockingExecutor { static EXECUTOR: Lazy<BlockingExecutor> = Lazy::new(|| BlockingExecutor { state: Mutex::new(State { idle_count: 0, thread_count: 0, queue: VecDeque::new(), }), cvar: Condvar::new(), }); &EXECUTOR } /// Spawns a future onto this executor. /// /// Returns a [`Task`] handle for the spawned task. pub fn spawn<T: Send + 'static>( &'static self, future: impl Future<Output = T> + Send + 'static, ) -> Task<T> { // Create a task, schedule it, and return its `Task` handle. let (runnable, handle) = async_task::spawn(future, move |r| self.schedule(r), ()); runnable.schedule(); Task(Some(handle)) } /// Runs the main loop on the current thread. /// /// This function runs blocking tasks until it becomes idle and times out. fn main_loop(&'static self) { let mut state = self.state.lock().unwrap(); loop { // This thread is not idle anymore because it's going to run tasks. state.idle_count -= 1; // Run tasks in the queue. while let Some(runnable) = state.queue.pop_front() { // We have found a task - grow the pool if needed. self.grow_pool(state); // Run the task. let _ = panic::catch_unwind(|| runnable.run()); // Re-lock the state and continue. state = self.state.lock().unwrap(); } // This thread is now becoming idle. state.idle_count += 1; // Put the thread to sleep until another task is scheduled. let timeout = Duration::from_millis(500); let (s, res) = self.cvar.wait_timeout(state, timeout).unwrap(); state = s; // If there are no tasks after a while, stop this thread. if res.timed_out() && state.queue.is_empty() { state.idle_count -= 1; state.thread_count -= 1; break; } } } /// Schedules a runnable task for execution. fn schedule(&'static self, runnable: Runnable) { let mut state = self.state.lock().unwrap(); state.queue.push_back(runnable); // Notify a sleeping thread and spawn more threads if needed. self.cvar.notify_one(); self.grow_pool(state); } /// Spawns more blocking threads if the pool is overloaded with work. fn grow_pool(&'static self, mut state: MutexGuard<'static, State>) { // If runnable tasks greatly outnumber idle threads and there aren't too many threads // already, then be aggressive: wake all idle threads and spawn one more thread. while state.queue.len() > state.idle_count * 5 && state.thread_count < 500 { // The new thread starts in idle state. state.idle_count += 1; state.thread_count += 1; // Notify all existing idle threads because we need to hurry up. self.cvar.notify_all(); // Spawn the new thread. thread::spawn(move || { // If enabled, set up tokio before the main loop begins. context::enter(|| self.main_loop()) }); } } } /// Spawns blocking code onto a thread. /// /// Note that `blocking!(expr)` is just syntax sugar for /// `Task::blocking(async move { expr }).await`. /// /// # Examples /// /// Read a file into a string: /// /// ```no_run /// use smol::blocking; /// use std::fs; /// /// # smol::run(async { /// let contents = blocking!(fs::read_to_string("file.txt"))?; /// # std::io::Result::Ok(()) }); /// ``` /// /// Spawn a process: /// /// ```no_run /// use smol::blocking; /// use std::process::Command; /// /// # smol::run(async { /// let out = blocking!(Command::new("dir").output())?; /// # std::io::Result::Ok(()) }); /// ``` #[macro_export] macro_rules! blocking { ($($expr:tt)*) => { $crate::Task::blocking(async move { $($expr)* }).await }; } /// Creates a stream that iterates on a thread. /// /// This adapter converts any kind of synchronous iterator into an asynchronous stream by running /// it on the blocking executor and sending items back over a channel. /// /// # Examples /// /// List files in the current directory: /// /// ```no_run /// use futures::stream::StreamExt; /// use smol::{blocking, iter}; /// use std::fs; /// /// # smol::run(async { /// // Load a directory. /// let mut dir = blocking!(fs::read_dir("."))?; /// let mut dir = iter(dir); /// /// // Iterate over the contents of the directory. /// while let Some(res) = dir.next().await { /// println!("{}", res?.file_name().to_string_lossy()); /// } /// # std::io::Result::Ok(()) }); /// ``` pub fn iter<T: Send + 'static>( iter: impl Iterator<Item = T> + Send + 'static, ) -> impl Stream<Item = T> + Send + Unpin + 'static { /// Current state of the iterator. enum State<T, I> { /// The iterator is idle. Idle(Option<I>), /// The iterator is running in a blocking task and sending items into a channel. Busy(piper::Receiver<T>, Task<I>), } impl<T, I> Unpin for State<T, I> {} impl<T: Send + 'static, I: Iterator<Item = T> + Send + 'static> Stream for State<T, I> { type Item = T; fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> { // Throttle if the current task has done too many I/O operations without yielding. futures_util::ready!(throttle::poll(cx)); match &mut *self { State::Idle(iter) => { // If idle, take the iterator out to run it on a blocking task. let mut iter = iter.take().unwrap(); // This channel capacity seems to work well in practice. If it's too low, there // will be too much synchronization between tasks. If too high, memory // consumption increases. let (sender, receiver) = piper::chan(8 * 1024); // 8192 items // Spawn a blocking task that runs the iterator and returns it when done. let task = Task::blocking(async move { for item in &mut iter { sender.send(item).await; } iter }); // Move into the busy state and poll again. *self = State::Busy(receiver, task); self.poll_next(cx) } State::Busy(receiver, task) => { // Poll the channel. let opt = futures_util::ready!(Pin::new(receiver).poll_next(cx)); // If the channel is closed, retrieve the iterator back from the blocking task. // This is not really a required step, but it's cleaner to drop the iterator on // the same thread that created it. if opt.is_none() { // Poll the task to retrieve the iterator. let iter = futures_util::ready!(Pin::new(task).poll(cx)); *self = State::Idle(Some(iter)); } Poll::Ready(opt) } } } } State::Idle(Some(iter)) } /// Creates an async reader that runs on a thread. /// /// This adapter converts any kind of synchronous reader into an asynchronous reader by running it /// on the blocking executor and sending bytes back over a pipe. /// /// # Examples /// /// Read from a file: /// /// ```no_run /// use futures::prelude::*; /// use smol::{blocking, reader}; /// use std::fs::File; /// /// # smol::run(async { /// // Open a file for reading. /// let file = blocking!(File::open("foo.txt"))?; /// let mut file = reader(file); /// /// // Read the whole file. /// let mut contents = Vec::new(); /// file.read_to_end(&mut contents).await?; /// # std::io::Result::Ok(()) }); /// ``` /// /// Read output from a process: /// /// ```no_run /// use futures::prelude::*; /// use smol::reader; /// use std::process::{Command, Stdio}; /// /// # smol::run(async { /// // Spawn a child process and make an async reader for its stdout. /// let child = Command::new("dir").stdout(Stdio::piped()).spawn()?; /// let mut child_stdout = reader(child.stdout.unwrap()); /// /// // Read the entire output. /// let mut output = String::new(); /// child_stdout.read_to_string(&mut output).await?; /// # std::io::Result::Ok(()) }); /// ``` pub fn reader(reader: impl Read + Send + 'static) -> impl AsyncRead + Send + Unpin + 'static { /// Current state of the reader. enum State<T> { /// The reader is idle. Idle(Option<T>), /// The reader is running in a blocking task and sending bytes into a pipe. Busy(piper::Reader, Task<(io::Result<()>, T)>), } impl<T: AsyncRead + Send + Unpin + 'static> AsyncRead for State<T> { fn poll_read( mut self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &mut [u8], ) -> Poll<io::Result<usize>> { // Throttle if the current task has done too many I/O operations without yielding. futures_util::ready!(throttle::poll(cx)); match &mut *self { State::Idle(io) => { // If idle, take the I/O handle out to read it on a blocking task. let mut io = io.take().unwrap(); // This pipe capacity seems to work well in practice. If it's too low, there // will be too much synchronization between tasks. If too high, memory // consumption increases. let (reader, mut writer) = piper::pipe(8 * 1024 * 1024); // 8 MB // Spawn a blocking task that reads and returns the I/O handle when done. let task = Task::blocking(async move { // Copy bytes from the I/O handle into the pipe until the pipe is closed or // an error occurs. let res = futures_util::io::copy(&mut io, &mut writer).await; (res.map(drop), io) }); // Move into the busy state and poll again. *self = State::Busy(reader, task); self.poll_read(cx, buf) } State::Busy(reader, task) => { // Poll the pipe. let n = futures_util::ready!(Pin::new(reader).poll_read(cx, buf))?; // If the pipe is closed, retrieve the I/O handle back from the blocking task. // This is not really a required step, but it's cleaner to drop the handle on // the same thread that created it. if n == 0 { // Poll the task to retrieve the I/O handle. let (res, io) = futures_util::ready!(Pin::new(task).poll(cx)); // Make sure to move into the idle state before reporting errors. *self = State::Idle(Some(io)); res?; } Poll::Ready(Ok(n)) } } } } // It's okay to treat the `Read` type as `AsyncRead` because it's only read from inside a // blocking task. let io = Box::pin(AllowStdIo::new(reader)); State::Idle(Some(io)) } /// Creates an async writer that runs on a thread. /// /// This adapter converts any kind of synchronous writer into an asynchronous writer by running it /// on the blocking executor and receiving bytes over a pipe. /// /// **Note:** Don't forget to flush the writer at the end, or some written bytes might get lost! /// /// # Examples /// /// Write into a file: /// /// ```no_run /// use futures::prelude::*; /// use smol::{blocking, writer}; /// use std::fs::File; /// /// # smol::run(async { /// // Open a file for writing. /// let file = blocking!(File::open("foo.txt"))?; /// let mut file = writer(file); /// /// // Write some bytes into the file and flush. /// file.write_all(b"hello").await?; /// file.flush().await?; /// # std::io::Result::Ok(()) }); /// ``` /// /// Write into standard output: /// /// ```no_run /// use futures::prelude::*; /// use smol::writer; /// /// # smol::run(async { /// // Create an async writer to stdout. /// let mut stdout = writer(std::io::stdout()); /// /// // Write a message and flush. /// stdout.write_all(b"hello").await?; /// stdout.flush().await?; /// # std::io::Result::Ok(()) }); /// ``` pub fn writer(writer: impl Write + Send + 'static) -> impl AsyncWrite + Send + Unpin + 'static { /// Current state of the writer. enum State<T> { /// The writer is idle. Idle(Option<T>), /// The writer is running in a blocking task and receiving bytes from a pipe. Busy(Option<piper::Writer>, Task<(io::Result<()>, T)>), } impl<T: AsyncWrite + Send + Unpin + 'static> State<T> { /// Starts a blocking task. fn start(&mut self) { if let State::Idle(io) = self { // If idle, take the I/O handle out to write on a blocking task. let mut io = io.take().unwrap(); // This pipe capacity seems to work well in practice. If it's too low, there will // be too much synchronization between tasks. If too high, memory consumption // increases. let (reader, writer) = piper::pipe(8 * 1024 * 1024); // 8 MB // Spawn a blocking task that writes and returns the I/O handle when done. let task = Task::blocking(async move { // Copy bytes from the pipe into the I/O handle until the pipe is closed or an // error occurs. Flush the I/O handle at the end. match futures_util::io::copy(reader, &mut io).await { Ok(_) => (io.flush().await, io), Err(err) => (Err(err), io), } }); // Move into the busy state. *self = State::Busy(Some(writer), task); } } } impl<T: AsyncWrite + Send + Unpin + 'static> AsyncWrite for State<T> { fn poll_write( mut self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &[u8], ) -> Poll<io::Result<usize>> { // Throttle if the current task has done too many I/O operations without yielding. futures_util::ready!(throttle::poll(cx)); loop { match &mut *self { // The writer is idle and closed. State::Idle(None) => return Poll::Ready(Ok(0)), // The writer is idle and open - start a blocking task. State::Idle(Some(_)) => self.start(), // The task is flushing and in process of stopping. State::Busy(None, task) => { // Poll the task to retrieve the I/O handle. let (res, io) = futures_util::ready!(Pin::new(task).poll(cx)); // Make sure to move into the idle state before reporting errors. *self = State::Idle(Some(io)); res?; } // The writer is busy - write more bytes into the pipe. State::Busy(Some(writer), _) => return Pin::new(writer).poll_write(cx, buf), } } } fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> { // Throttle if the current task has done too many I/O operations without yielding. futures_util::ready!(throttle::poll(cx)); loop { match &mut *self { // The writer is idle and closed. State::Idle(None) => return Poll::Ready(Ok(())), // The writer is idle and open - start a blocking task. State::Idle(Some(_)) => self.start(), // The task is busy. State::Busy(writer, task) => { // Drop the writer to close the pipe. This stops the `futures_util::io::copy` // operation in the task, after which the task flushes the I/O handle and // returns it back. writer.take(); // Poll the task to retrieve the I/O handle. let (res, io) = futures_util::ready!(Pin::new(task).poll(cx)); // Make sure to move into the idle state before reporting errors. *self = State::Idle(Some(io)); return Poll::Ready(res); } } } } fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> { // First, make sure the I/O handle is flushed. futures_util::ready!(Pin::new(&mut *self).poll_flush(cx))?; // Then move into the idle state with no I/O handle, thus dropping it. *self = State::Idle(None); Poll::Ready(Ok(())) } } // It's okay to treat the `Write` type as `AsyncWrite` because it's only written to inside a // blocking task. let io = AllowStdIo::new(writer); State::Idle(Some(io)) }