Merge rayon-rs#636

636: Add the ability to customize thread spawning r=nikomatsakis a=cuviper

As an alternative to `ThreadPoolBuilder::build()` and `build_global()`,
the new `spawn()` and `spawn_global()` methods take a closure which will
be responsible for spawning the actual threads. This is called with a
`ThreadBuilder` argument that provides the thread index, name, and stack
size, with the expectation to call its `run()` method in the new thread.

The motivating use cases for this are:
- experimental WASM threading, to be externally implemented.
- scoped threads, like the new test using `scoped_tls`.

Co-authored-by: Josh Stone <cuviper@gmail.com>

Author: bors[bot]

rayon-core/Cargo.toml

@@ -19,10 +19,12 @@ num_cpus = "1.2"
 lazy_static = "1"
 crossbeam-deque = "0.6.3"
 crossbeam-queue = "0.1.2"
+crossbeam-utils = "0.6.5"
 
 [dev-dependencies]
 rand = "0.6"
 rand_xorshift = "0.1"
+scoped-tls = "1.0"
 
 [target.'cfg(unix)'.dev-dependencies]
 libc = "0.2"
@@ -49,3 +51,7 @@ path = "tests/scope_join.rs"
 [[test]]
 name = "simple_panic"
 path = "tests/simple_panic.rs"
+
+[[test]]
+name = "scoped_threadpool"
+path = "tests/scoped_threadpool.rs"

rayon-core/src/lib.rs

@@ -34,6 +34,7 @@ use std::str::FromStr;
 
 extern crate crossbeam_deque;
 extern crate crossbeam_queue;
+extern crate crossbeam_utils;
 #[cfg(any(debug_assertions, rayon_unstable))]
 #[macro_use]
 extern crate lazy_static;
@@ -46,6 +47,8 @@ extern crate rand_xorshift;
 
 #[macro_use]
 mod log;
+#[macro_use]
+mod private;
 
 mod job;
 mod join;
@@ -64,13 +67,16 @@ mod test;
 #[cfg(rayon_unstable)]
 pub mod internal;
 pub use join::{join, join_context};
+pub use registry::ThreadBuilder;
 pub use scope::{scope, Scope};
 pub use scope::{scope_fifo, ScopeFifo};
 pub use spawn::{spawn, spawn_fifo};
 pub use thread_pool::current_thread_has_pending_tasks;
 pub use thread_pool::current_thread_index;
 pub use thread_pool::ThreadPool;
 
+use registry::{CustomSpawn, DefaultSpawn, ThreadSpawn};
+
 /// Returns the number of threads in the current registry. If this
 /// code is executing within a Rayon thread-pool, then this will be
 /// the number of threads for the thread-pool of the current
@@ -123,8 +129,7 @@ enum ErrorKind {
 ///
 /// [`ThreadPool`]: struct.ThreadPool.html
 /// [`build_global()`]: struct.ThreadPoolBuilder.html#method.build_global
-#[derive(Default)]
-pub struct ThreadPoolBuilder {
+pub struct ThreadPoolBuilder<S = DefaultSpawn> {
     /// The number of threads in the rayon thread pool.
     /// If zero will use the RAYON_NUM_THREADS environment variable.
     /// If RAYON_NUM_THREADS is invalid or zero will use the default.
@@ -146,6 +151,9 @@ pub struct ThreadPoolBuilder {
     /// Closure invoked on worker thread exit.
     exit_handler: Option<Box<ExitHandler>>,
 
+    /// Closure invoked to spawn threads.
+    spawn_handler: S,
+
     /// If false, worker threads will execute spawned jobs in a
     /// "depth-first" fashion. If true, they will do a "breadth-first"
     /// fashion. Depth-first is the default.
@@ -174,12 +182,35 @@ type StartHandler = Fn(usize) + Send + Sync;
 /// Note that this same closure may be invoked multiple times in parallel.
 type ExitHandler = Fn(usize) + Send + Sync;
 
+// NB: We can't `#[derive(Default)]` because `S` is left ambiguous.
+impl Default for ThreadPoolBuilder {
+    fn default() -> Self {
+        ThreadPoolBuilder {
+            num_threads: 0,
+            panic_handler: None,
+            get_thread_name: None,
+            stack_size: None,
+            start_handler: None,
+            exit_handler: None,
+            spawn_handler: DefaultSpawn,
+            breadth_first: false,
+        }
+    }
+}
+
 impl ThreadPoolBuilder {
     /// Creates and returns a valid rayon thread pool builder, but does not initialize it.
-    pub fn new() -> ThreadPoolBuilder {
-        ThreadPoolBuilder::default()
+    pub fn new() -> Self {
+        Self::default()
     }
+}
 
+/// Note: the `S: ThreadSpawn` constraint is an internal implementation detail for the
+/// default spawn and those set by [`spawn_handler`](#method.spawn_handler).
+impl<S> ThreadPoolBuilder<S>
+where
+    S: ThreadSpawn,
+{
     /// Create a new `ThreadPool` initialized using this configuration.
     pub fn build(self) -> Result<ThreadPool, ThreadPoolBuildError> {
         ThreadPool::build(self)
@@ -207,6 +238,154 @@ impl ThreadPoolBuilder {
         registry.wait_until_primed();
         Ok(())
     }
+}
+
+impl ThreadPoolBuilder {
+    /// Create a scoped `ThreadPool` initialized using this configuration.
+    ///
+    /// This is a convenience function for building a pool using [`crossbeam::scope`]
+    /// to spawn threads in a [`spawn_handler`](#method.spawn_handler).
+    /// The threads in this pool will start by calling `wrapper`, which should
+    /// do initialization and continue by calling `ThreadBuilder::run()`.
+    ///
+    /// [`crossbeam::scope`]: https://docs.rs/crossbeam/0.7/crossbeam/fn.scope.html
+    ///
+    /// # Examples
+    ///
+    /// A scoped pool may be useful in combination with scoped thread-local variables.
+    ///
+    /// ```
+    /// #[macro_use]
+    /// extern crate scoped_tls;
+    /// # use rayon_core as rayon;
+    ///
+    /// scoped_thread_local!(static POOL_DATA: Vec<i32>);
+    ///
+    /// fn main() -> Result<(), rayon::ThreadPoolBuildError> {
+    ///     let pool_data = vec![1, 2, 3];
+    ///
+    ///     // We haven't assigned any TLS data yet.
+    ///     assert!(!POOL_DATA.is_set());
+    ///
+    ///     rayon::ThreadPoolBuilder::new()
+    ///         .build_scoped(
+    ///             // Borrow `pool_data` in TLS for each thread.
+    ///             |thread| POOL_DATA.set(&pool_data, || thread.run()),
+    ///             // Do some work that needs the TLS data.
+    ///             |pool| pool.install(|| assert!(POOL_DATA.is_set())),
+    ///         )?;
+    ///
+    ///     // Once we've returned, `pool_data` is no longer borrowed.
+    ///     drop(pool_data);
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn build_scoped<W, F, R>(self, wrapper: W, with_pool: F) -> Result<R, ThreadPoolBuildError>
+    where
+        W: Fn(ThreadBuilder) + Sync, // expected to call `run()`
+        F: FnOnce(&ThreadPool) -> R,
+    {
+        let result = crossbeam_utils::thread::scope(|scope| {
+            let wrapper = &wrapper;
+            let pool = self
+                .spawn_handler(|thread| {
+                    let mut builder = scope.builder();
+                    if let Some(name) = thread.name() {
+                        builder = builder.name(name.to_string());
+                    }
+                    if let Some(size) = thread.stack_size() {
+                        builder = builder.stack_size(size);
+                    }
+                    builder.spawn(move |_| wrapper(thread))?;
+                    Ok(())
+                })
+                .build()?;
+            Ok(with_pool(&pool))
+        });
+
+        match result {
+            Ok(result) => result,
+            Err(err) => unwind::resume_unwinding(err),
+        }
+    }
+}
+
+impl<S> ThreadPoolBuilder<S> {
+    /// Set a custom function for spawning threads.
+    ///
+    /// Note that the threads will not exit until after the pool is dropped. It
+    /// is up to the caller to wait for thread termination if that is important
+    /// for any invariants. For instance, threads created in [`crossbeam::scope`]
+    /// will be joined before that scope returns, and this will block indefinitely
+    /// if the pool is leaked. Furthermore, the global thread pool doesn't terminate
+    /// until the entire process exits!
+    ///
+    /// [`crossbeam::scope`]: https://docs.rs/crossbeam/0.7/crossbeam/fn.scope.html
+    ///
+    /// # Examples
+    ///
+    /// A minimal spawn handler just needs to call `run()` from an independent thread.
+    ///
+    /// ```
+    /// # use rayon_core as rayon;
+    /// fn main() -> Result<(), rayon::ThreadPoolBuildError> {
+    ///     let pool = rayon::ThreadPoolBuilder::new()
+    ///         .spawn_handler(|thread| {
+    ///             std::thread::spawn(|| thread.run());
+    ///             Ok(())
+    ///         })
+    ///         .build()?;
+    ///
+    ///     pool.install(|| println!("Hello from my custom thread!"));
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// The default spawn handler sets the name and stack size if given, and propagates
+    /// any errors from the thread builder.
+    ///
+    /// ```
+    /// # use rayon_core as rayon;
+    /// fn main() -> Result<(), rayon::ThreadPoolBuildError> {
+    ///     let pool = rayon::ThreadPoolBuilder::new()
+    ///         .spawn_handler(|thread| {
+    ///             let mut b = std::thread::Builder::new();
+    ///             if let Some(name) = thread.name() {
+    ///                 b = b.name(name.to_owned());
+    ///             }
+    ///             if let Some(stack_size) = thread.stack_size() {
+    ///                 b = b.stack_size(stack_size);
+    ///             }
+    ///             b.spawn(|| thread.run())?;
+    ///             Ok(())
+    ///         })
+    ///         .build()?;
+    ///
+    ///     pool.install(|| println!("Hello from my fully custom thread!"));
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn spawn_handler<F>(self, spawn: F) -> ThreadPoolBuilder<CustomSpawn<F>>
+    where
+        F: FnMut(ThreadBuilder) -> io::Result<()>,
+    {
+        ThreadPoolBuilder {
+            spawn_handler: CustomSpawn::new(spawn),
+            // ..self
+            num_threads: self.num_threads,
+            panic_handler: self.panic_handler,
+            get_thread_name: self.get_thread_name,
+            stack_size: self.stack_size,
+            start_handler: self.start_handler,
+            exit_handler: self.exit_handler,
+            breadth_first: self.breadth_first,
+        }
+    }
+
+    /// Returns a reference to the current spawn handler.
+    fn get_spawn_handler(&mut self) -> &mut S {
+        &mut self.spawn_handler
+    }
 
     /// Get the number of threads that will be used for the thread
     /// pool. See `num_threads()` for more information.
@@ -276,7 +455,7 @@ impl ThreadPoolBuilder {
     /// replacement of the now deprecated `RAYON_RS_NUM_CPUS` environment
     /// variable. If both variables are specified, `RAYON_NUM_THREADS` will
     /// be prefered.
-    pub fn num_threads(mut self, num_threads: usize) -> ThreadPoolBuilder {
+    pub fn num_threads(mut self, num_threads: usize) -> Self {
         self.num_threads = num_threads;
         self
     }
@@ -300,7 +479,7 @@ impl ThreadPoolBuilder {
     /// If the panic handler itself panics, this will abort the
     /// process. To prevent this, wrap the body of your panic handler
     /// in a call to `std::panic::catch_unwind()`.
-    pub fn panic_handler<H>(mut self, panic_handler: H) -> ThreadPoolBuilder
+    pub fn panic_handler<H>(mut self, panic_handler: H) -> Self
     where
         H: Fn(Box<Any + Send>) + Send + Sync + 'static,
     {
@@ -368,7 +547,7 @@ impl ThreadPoolBuilder {
     /// Note that this same closure may be invoked multiple times in parallel.
     /// If this closure panics, the panic will be passed to the panic handler.
     /// If that handler returns, then startup will continue normally.
-    pub fn start_handler<H>(mut self, start_handler: H) -> ThreadPoolBuilder
+    pub fn start_handler<H>(mut self, start_handler: H) -> Self
     where
         H: Fn(usize) + Send + Sync + 'static,
     {
@@ -387,7 +566,7 @@ impl ThreadPoolBuilder {
     /// Note that this same closure may be invoked multiple times in parallel.
     /// If this closure panics, the panic will be passed to the panic handler.
     /// If that handler returns, then the thread will exit normally.
-    pub fn exit_handler<H>(mut self, exit_handler: H) -> ThreadPoolBuilder
+    pub fn exit_handler<H>(mut self, exit_handler: H) -> Self
     where
         H: Fn(usize) + Send + Sync + 'static,
     {
@@ -503,7 +682,7 @@ pub fn initialize(config: Configuration) -> Result<(), Box<Error>> {
     config.into_builder().build_global().map_err(Box::from)
 }
 
-impl fmt::Debug for ThreadPoolBuilder {
+impl<S> fmt::Debug for ThreadPoolBuilder<S> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         let ThreadPoolBuilder {
             ref num_threads,
@@ -512,6 +691,7 @@ impl fmt::Debug for ThreadPoolBuilder {
             ref stack_size,
             ref start_handler,
             ref exit_handler,
+            spawn_handler: _,
             ref breadth_first,
         } = *self;
 

rayon-core/src/private.rs

@@ -0,0 +1,26 @@
+//! The public parts of this private module are used to create traits
+//! that cannot be implemented outside of our own crate.  This way we
+//! can feel free to extend those traits without worrying about it
+//! being a breaking change for other implementations.
+
+/// If this type is pub but not publicly reachable, third parties
+/// can't name it and can't implement traits using it.
+#[allow(missing_debug_implementations)]
+pub struct PrivateMarker;
+
+macro_rules! private_decl {
+    () => {
+        /// This trait is private; this method exists to make it
+        /// impossible to implement outside the crate.
+        #[doc(hidden)]
+        fn __rayon_private__(&self) -> ::private::PrivateMarker;
+    }
+}
+
+macro_rules! private_impl {
+    () => {
+        fn __rayon_private__(&self) -> ::private::PrivateMarker {
+            ::private::PrivateMarker
+        }
+    }
+}