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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671
//! [![Documentation](https://docs.rs/ste/badge.svg)](https://docs.rs/ste) //! [![Crates](https://img.shields.io/crates/v/ste.svg)](https://crates.io/crates/ste) //! [![Actions Status](https://github.com/udoprog/audio/workflows/Rust/badge.svg)](https://github.com/udoprog/audio/actions) //! //! A single-threaded executor with some tricks up its sleeve. //! //! This was primarily written for use in [audio] as a low-latency way of //! interacting with a single background thread for audio-related purposes, but //! is otherwise a general purpose library that can be used to do anything. //! //! > **Soundness Warning:** This crate uses a fair bit of **unsafe**. Some of //! > the tricks employed needs to be rigirously sanity checked for safety //! > before you can rely on this for production uses. //! //! The default way to access the underlying thread is through the [submit] //! method. This blocks the current thread for the duration of the task allowing //! the background thread to access variables which are in scope. Like `n` //! below. //! //! ```rust //! # fn main() -> anyhow::Result<()> { //! let thread = ste::Thread::new()?; //! //! let mut n = 10; //! thread.submit(|| n += 10)?; //! assert_eq!(20, n); //! //! thread.join()?; //! # Ok(()) } //! ``` //! //! # Restricting thread access using tags //! //! This library provides the ability to construct a [Tag] which is uniquely //! associated with the thread that created it. This can then be used to ensure //! that data is only accessible by one thread. //! //! This is useful, because many APIs requires *thread-locality* where instances //! can only safely be used by the thread that created them. This is a low-level //! tool we provide which allows the safe implementation of `Send` for types //! which are otherwise `!Send`. //! //! Note that correctly using a [Tag] is hard, and incorrect use has severe //! safety implications. Make sure to study its documentation closely before //! use. //! //! ```rust //! struct Foo { //! tag: ste::Tag, //! } //! //! impl Foo { //! fn new() -> Self { //! Self { //! tag: ste::Tag::current_thread(), //! } //! } //! //! fn say_hello(&self) { //! self.tag.ensure_on_thread(); //! println!("Hello World!"); //! } //! } //! //! # fn main() -> anyhow::Result<()> { //! let thread = ste::Thread::new()?; //! //! let foo = thread.submit(|| Foo::new())?; //! //! thread.submit(|| { //! foo.say_hello(); // <- OK! //! })?; //! //! thread.join()?; //! # Ok(()) } //! ``` //! //! Using `say_hello` outside of the thread that created it is not fine and will //! panic to prevent racy access: //! //! ```rust,should_panic //! # struct Foo { tag: ste::Tag } //! # impl Foo { //! # fn new() -> Self { Self { tag: ste::Tag::current_thread() } } //! # fn say_hello(&self) { self.tag.ensure_on_thread(); } //! # } //! # fn main() -> anyhow::Result<()> { //! let thread = ste::Thread::new()?; //! //! let foo = thread.submit(|| Foo::new())?; //! //! foo.say_hello(); // <- Oops, panics! //! //! thread.join()?; //! # Ok(()) } //! ``` //! //! # Known unsafety and soundness issues //! //! Below you can find a list of unsafe use and known soundness issues this //! library currently has. The soundness issues **must be fixed** before this //! library goes out of *alpha*. //! //! ## Pointers to stack-local addresses //! //! In order to efficiently share data between a thread calling [submit] and the //! background thread, the background thread references a fair bit of //! stack-local data from the calling thread which involves a fair bit of //! `unsafe`. //! //! While it should be possible to make this use *safe* (as is the hope of this //! library), it carries a risk that if the background thread were to proceed //! executing a task that is no longer synchronized properly with a caller of //! [submit] it might end up referencing data which is either no longer valid //! (use after free), or contains something else (dirty). //! //! ## Tag re-use //! //! [Tag] containers currently use a tag based on the address of a slab of //! allocated memory that is associated with each [Thread]. If however a //! [Thread] is shut down, and a new later recreated, there is a slight risk //! that this might re-use an existing memory address. //! //! Memory addresses are quite thankful to use, because they're cheap and quite //! easy to access. Due to this it might however be desirable to use a generated //! ID per thread instead which can for example abort a program in case it can't //! guarantee uniqueness. //! //! [submit]: https://docs.rs/ste/0.1.0-alpha.9/ste/struct.Thread.html#method.submit //! [Thread]: https://docs.rs/ste/0.1.0-alpha.9/ste/struct.Thread.html //! [Tag]: https://docs.rs/ste/0.1.0-alpha.9/ste/struct.Tag.html //! [audio]: https://github.com/udoprog/audio use std::future::Future; use std::io; use std::mem; use std::ptr; use thiserror::Error; pub(crate) mod loom; use self::loom::thread; #[cfg(test)] mod tests; mod parker; use crate::parker::Parker; mod worker; use self::worker::{Entry, Prelude, ScheduleEntry, Shared}; mod tag; use self::tag::with_tag; pub use self::tag::Tag; #[doc(hidden)] pub mod linked_list; mod adapter; use self::adapter::{Adapter, FutureAdapter}; mod wait_future; use self::wait_future::WaitFuture; /// Error raised when we try to interact with a background thread that has /// panicked. #[derive(Debug, Error)] #[error("background thread panicked")] pub struct Panicked(()); /// The handle for a background thread. /// /// The background thread can be interacted with in a couple of ways: /// * [submit][Thread::submit] - for submitted tasks, the call will block until /// it has been executed on the thread (or the thread has panicked). /// * [submit_async][Thread::submit_async] - for submitting asynchronous tasks, /// the call will block until it has been executed on the thread (or the /// thread has panicked). /// * [drop][Thread::drop] - for dropping value *on* the background thread. This /// is necessary for [Tag] values that requires drop. /// /// # Tasks panicking /// /// If anything on the background thread ends up panicking, any future submitted /// tasks will return the [Panicked] error. Joining the thread with /// [join][Thread::join] will also report [Panicked]. /// /// # Examples /// /// ```rust /// use std::sync::Arc; /// /// # fn main() -> anyhow::Result<()> { /// let thread = Arc::new(ste::Thread::new()?); /// let mut threads = Vec::new(); /// /// for n in 0..10 { /// let thread = thread.clone(); /// /// threads.push(std::thread::spawn(move || { /// thread.submit(move || n) /// })); /// } /// /// let mut result = 0; /// /// for t in threads { /// result += t.join().unwrap()?; /// } /// /// assert_eq!(result, (0..10).sum()); /// /// // Unwrap the thread. /// let thread = Arc::try_unwrap(thread).map_err(|_| "unwrap failed").unwrap(); /// /// let result = thread.submit(|| { /// panic!("Background thread: {:?}", std::thread::current().id()); /// }); /// assert!(result.is_err()); /// /// println!("Main thread: {:?}", std::thread::current().id()); /// /// thread.join()?; /// # Ok(()) } /// ``` #[must_use = "The thread should be joined with Thread::join once no longer used, \ otherwise it will block while being dropped."] pub struct Thread { /// Things that have been submitted for execution on the background thread. shared: ptr::NonNull<Shared>, /// The handle associated with the background thread. handle: Option<thread::JoinHandle<()>>, } /// Safety: The handle is both send and sync because it joins the background /// thread which keeps track of the state of `shared` and cleans it up once it's /// no longer needed. unsafe impl Send for Thread {} unsafe impl Sync for Thread {} impl Thread { /// Construct a default background thread executor. /// /// These both do the same thing: /// /// ```rust /// # fn main() -> anyhow::Result<()> { /// let thread1 = ste::Thread::new()?; /// let thread2 = ste::Builder::new().build()?; /// # Ok(()) } /// ``` pub fn new() -> io::Result<Self> { Builder::new().build() } /// Submit a task to run on the background thread. /// /// The call will block until it has been executed on the thread (or the /// thread has panicked). /// /// Because this function blocks until completion, it can safely access /// values which are outside of the scope of the provided closure. /// /// If you however need to store and access things which are `!Send`, you /// can wrap them in a container that ensures their thread-locality with /// [Tag] and then safely implement [Send] for it. /// /// # Examples /// /// ```rust /// # fn main() -> anyhow::Result<()> { /// let thread = ste::Thread::new()?; /// /// let mut n = 10; /// thread.submit(|| n += 10)?; /// assert_eq!(20, n); /// /// thread.join()?; /// # Ok(()) } /// ``` /// /// Unwinding panics as isolated on a per-task basis. /// /// ```rust /// # #[tokio::main(flavor = "current_thread")] /// # async fn main() -> anyhow::Result<()> { /// let thread = ste::Thread::new()?; /// /// let result = thread.submit(|| panic!("woops")); /// assert!(result.is_err()); /// /// let mut result = 0; /// thread.submit(|| { result += 1 })?; /// assert_eq!(result, 1); /// /// thread.join()?; /// # Ok(()) } /// ``` pub fn submit<F, T>(&self, task: F) -> Result<T, Panicked> where F: Send + FnOnce() -> T, T: Send, { unsafe { let mut storage = None; let parker = Parker::new(); let mut task = into_task(task, ptr::NonNull::from(&mut storage)); let entry = ScheduleEntry::new( ptr::NonNull::new_unchecked(mem::transmute::<&mut (dyn FnMut(Tag) + Send), _>( &mut task, )), ptr::NonNull::from(&parker), ); // Safety: We're constructing a pointer to a local stack location. It // will never be null. // // The transmute is necessary because we're constructing a trait object // with a `'static` lifetime. self.shared .as_ref() .schedule_in_place(ptr::NonNull::from(&parker), Entry::Schedule(entry))?; return match storage { Some(result) => Ok(result), None => Err(Panicked(())), }; } fn into_task<T, O>(task: T, storage: ptr::NonNull<Option<O>>) -> impl FnMut(Tag) + Send where T: FnOnce() -> O + Send, O: Send, { let mut task = Some(task); let storage = RawSend(storage); move |tag| { let RawSend(mut storage) = storage; if let Some(task) = task.take() { let output = with_tag(tag, task); // Safety: we're the only one with access to this pointer, // and we know it hasn't been de-allocated yet. unsafe { *storage.as_mut() = Some(output); } } } } } /// Run the given future on the background thread. The future can reference /// memory outside of the current scope, but in order to do so, every time /// it is polled it has to be perfectly synchronized with a remote poll /// happening on the background thread. /// /// # Safety /// /// This function is unsafe as heck right now. Polling it without it having /// been called w/ wake_by_ref **will cause a data race**. /// /// The above will be fixed. /// /// # Examples /// /// This method supports panics the same way as other threads: /// /// ```rust /// # #[tokio::main(flavor = "current_thread")] /// # async fn main() -> anyhow::Result<()> { /// let thread = ste::Builder::new().with_tokio().build()?; /// /// thread.submit_async(async { /// tokio::time::sleep(std::time::Duration::from_secs(1)).await; /// println!("Hello World!"); /// }); /// /// thread.join()?; /// # Ok(()) } /// ``` /// /// Unwinding panics as isolated on a per-task basis the same was as for /// [submit][Thread::submit]. /// /// ```rust /// # #[tokio::main(flavor = "current_thread")] /// # async fn main() -> anyhow::Result<()> { /// let thread = ste::Thread::new()?; /// /// let result = thread.submit_async(async move { panic!("woops") }).await; /// assert!(result.is_err()); /// /// let mut result = 0; /// thread.submit_async(async { result += 1 }).await?; /// assert_eq!(result, 1); /// /// thread.join()?; /// # Ok(()) } /// ``` pub async fn submit_async<F>(&self, mut future: F) -> Result<F::Output, Panicked> where F: Send + Future, F::Output: Send, { // Parker to use during polling. let parker = Parker::new(); // Stack location where the output of the compuation is stored. let mut output = None; // Static adapter for the future. let mut adapter = FutureAdapter::new( ptr::NonNull::from(&mut future), ptr::NonNull::from(&mut output), ); unsafe { let wait_future = WaitFuture { adapter: { // Note: the transmute is necessary to extend the lifetime // of the adapter so that it can be send to the thread. // // That's because trait objects behind raw pointers still // require lifetimes (for some reason). ptr::NonNull::from(mem::transmute::<&mut dyn Adapter, &mut dyn Adapter>( &mut adapter, )) }, parker: ptr::NonNull::from(&parker), complete: false, shared: self.shared.as_ref(), output: ptr::NonNull::from(&mut output), }; wait_future.await } } /// Move the provided `value` onto the background thread and drop it. /// /// This is necessary for values which uses [Tag] to ensure that a type is /// not dropped incorrectly. /// /// # Examples /// /// ```rust /// struct Foo(ste::Tag); /// /// impl Drop for Foo { /// fn drop(&mut self) { /// self.0.ensure_on_thread(); /// } /// } /// /// # fn main() -> anyhow::Result<()> { /// let thread = ste::Thread::new()?; /// /// let foo = thread.submit(|| Foo(ste::Tag::current_thread())); /// thread.drop(foo); /// /// thread.join()?; /// # Ok(()) } /// ``` pub fn drop<T>(&self, value: T) -> Result<(), Panicked> where T: Send, { self.submit(move || drop(value))?; Ok(()) } /// Join the background thread. /// /// Will block until the background thread is joined. /// /// This is the clean way to join a background thread, the alternative is to /// let [Thread] drop and this will be performed in the drop handler /// instead. /// /// Always returns the error [Panicked] if the background thread has /// panicked from a submitted task. /// /// # Examples /// /// ```rust /// # fn main() -> anyhow::Result<()> { /// let thread = ste::Thread::new()?; /// /// let mut n = 10; /// thread.submit(|| n += 10)?; /// assert_eq!(20, n); /// /// thread.join()?; /// # Ok(()) } /// ``` pub fn join(mut self) -> Result<(), Panicked> { if let Some(handle) = self.handle.take() { unsafe { self.shared.as_ref().outer_join() }; return handle.join().map_err(|_| Panicked(())); } Ok(()) } /// Construct the tag that is associated with the current thread externally /// from the thread. /// /// # Examples /// /// ```rust /// struct Foo(ste::Tag); /// /// impl Foo { /// fn say_hello(&self) { /// self.0.ensure_on_thread(); /// println!("Hello World"); /// } /// } /// /// # fn main() -> anyhow::Result<()> { /// let thread = ste::Thread::new()?; /// /// let foo = Foo(thread.tag()); /// /// thread.submit(|| { /// foo.say_hello(); /// })?; /// /// thread.join()?; /// # Ok(()) } /// ``` pub fn tag(&self) -> Tag { Tag(self.shared.as_ptr() as usize) } } impl Drop for Thread { fn drop(&mut self) { // Note: we can safely ignore the result, because it will only error in // case the background thread has panicked. At which point we're still // free to assume it's no longer using the shared state. if let Some(handle) = self.handle.take() { unsafe { self.shared.as_ref().outer_join() }; let _ = handle.join(); } // Safety: at this point it's guaranteed that we've synchronized with // the thread enough that the shared state can be safely deallocated. // // The background thread is in one of two states: // * It has panicked, which means the shared state will not be used any // longer. // * It has successfully been joined in. Which has the same // implications. unsafe { let _ = Box::from_raw(self.shared.as_ptr()); } } } /// The builder for a [Thread] which can be configured a bit more. pub struct Builder { prelude: Option<Box<Prelude>>, #[cfg(feature = "tokio")] tokio: Option<tokio::runtime::Handle>, } impl Builder { /// Construct a new builder. pub fn new() -> Self { Self { prelude: None, #[cfg(feature = "tokio")] tokio: None, } } /// Enable tokio support. /// /// # Examples /// /// ```rust /// # #[tokio::main(flavor = "current_thread")] /// # async fn main() -> anyhow::Result<()> { /// let thread = ste::Builder::new().with_tokio().build()?; /// /// thread.submit_async(async { /// tokio::time::sleep(std::time::Duration::from_secs(1)).await; /// println!("Hello World!"); /// }); /// /// thread.join()?; /// # Ok(()) } /// ``` #[cfg(feature = "tokio")] #[cfg_attr(docsrs, doc(cfg(feature = "tokio")))] pub fn with_tokio(self) -> Self { Self { tokio: Some(::tokio::runtime::Handle::current()), ..self } } /// Configure a prelude to the [Thread]. This is code that will run just as /// the thread is spinning up. /// /// # Examples /// /// ```rust /// fn say_hello(main_thread: std::thread::ThreadId) { /// println!("Hello from the prelude!"); /// assert_ne!(main_thread, std::thread::current().id()); /// } /// /// # fn main() -> anyhow::Result<()> { /// let main_thread = std::thread::current().id(); /// /// let thread = ste::Builder::new().prelude(move || say_hello(main_thread)).build(); /// # Ok(()) } /// ``` pub fn prelude<P>(self, prelude: P) -> Self where P: Fn() + Send + 'static, { Self { prelude: Some(Box::new(prelude)), ..self } } /// Construct the background thread. /// /// # Examples /// /// ```rust /// # fn main() -> anyhow::Result<()> { /// let thread = ste::Builder::new().build()?; /// thread.join()?; /// # Ok(()) } /// ``` pub fn build(self) -> io::Result<Thread> { let shared = ptr::NonNull::from(Box::leak(Box::new(Shared::new()))); let prelude = self.prelude; #[cfg(feature = "tokio")] let tokio = self.tokio; let shared2 = RawSend(shared); let handle = thread::Builder::new() .name(String::from("ste-thread")) .spawn(move || { let RawSend(shared) = shared2; #[cfg(feature = "tokio")] let _guard = tokio.as_ref().map(|h| h.enter()); worker::run(prelude, shared) })?; Ok(Thread { shared, handle: Some(handle), }) } } /// Small helper for sending things which are not Send. struct RawSend<T>(ptr::NonNull<T>); unsafe impl<T> Send for RawSend<T> {}