impl ThreadPool

fn new(configuration: Configuration) -> Result<ThreadPool, Box<dyn Error>>

Deprecated in favor of ThreadPoolBuilder::build.

fn install<OP, R>(&self, op: OP) -> R
where
    OP: FnOnce() -> R + Send,
    R: Send,

Executes op within the thread pool. Any attempts to use join, scope, or parallel iterators will then operate within that thread pool.

Warning: thread-local data

Because op is executing within the Rayon thread pool, thread-local data from the current thread will not be accessible.

Warning: execution order

If the current thread is part of a different thread pool, it will try to keep busy while the op completes in its target pool, similar to calling [ThreadPool::yield_now()] in a loop. Therefore, it may potentially schedule other tasks to run on the current thread in the meantime. For example

# use rayon_core as rayon;
fn main() {
    rayon::ThreadPoolBuilder::new().num_threads(1).build_global().unwrap();
    let pool = rayon_core::ThreadPoolBuilder::default().build().unwrap();
    let do_it = || {
        print!("one ");
        pool.install(||{});
        print!("two ");
    };
    rayon::join(|| do_it(), || do_it());
}

Since we configured just one thread in the global pool, one might expect do_it() to run sequentially, producing:

one two one two

However each call to install() yields implicitly, allowing rayon to run multiple instances of do_it() concurrently on the single, global thread. The following output would be equally valid:

one one two two

Panics

If op should panic, that panic will be propagated.

Using install()

   # use rayon_core as rayon;
   fn main() {
        let pool = rayon::ThreadPoolBuilder::new().num_threads(8).build().unwrap();
        let n = pool.install(|| fib(20));
        println!("{}", n);
   }

   fn fib(n: usize) -> usize {
        if n == 0 || n == 1 {
            return n;
        }
        let (a, b) = rayon::join(|| fib(n - 1), || fib(n - 2)); // runs inside of `pool`
        return a + b;
    }

fn broadcast<OP, R>(&self, op: OP) -> Vec<R>
where
    OP: Fn(BroadcastContext<'_>) -> R + Sync,
    R: Send,

Executes op within every thread in the thread pool. Any attempts to use join, scope, or parallel iterators will then operate within that thread pool.

Broadcasts are executed on each thread after they have exhausted their local work queue, before they attempt work-stealing from other threads. The goal of that strategy is to run everywhere in a timely manner without being too disruptive to current work. There may be alternative broadcast styles added in the future for more or less aggressive injection, if the need arises.

Warning: thread-local data

Because op is executing within the Rayon thread pool, thread-local data from the current thread will not be accessible.

Panics

If op should panic on one or more threads, exactly one panic will be propagated, only after all threads have completed (or panicked) their own op.

Examples

   # use rayon_core as rayon;
   use std::sync::atomic::{AtomicUsize, Ordering};

   fn main() {
        let pool = rayon::ThreadPoolBuilder::new().num_threads(5).build().unwrap();

        // The argument gives context, including the index of each thread.
        let v: Vec<usize> = pool.broadcast(|ctx| ctx.index() * ctx.index());
        assert_eq!(v, &[0, 1, 4, 9, 16]);

        // The closure can reference the local stack
        let count = AtomicUsize::new(0);
        pool.broadcast(|_| count.fetch_add(1, Ordering::Relaxed));
        assert_eq!(count.into_inner(), 5);
   }

fn current_num_threads(&self) -> usize

Returns the (current) number of threads in the thread pool.

Future compatibility note

Note that unless this thread pool was created with a ThreadPoolBuilder that specifies the number of threads, then this number may vary over time in future versions (see the num_threads() method for details).

fn current_thread_index(&self) -> Option<usize>

If called from a Rayon worker thread in this thread pool, returns the index of that thread; if not called from a Rayon thread, or called from a Rayon thread that belongs to a different thread pool, returns None.

The index for a given thread will not change over the thread's lifetime. However, multiple threads may share the same index if they are in distinct thread pools.

Future compatibility note

Currently, every thread pool (including the global thread pool) has a fixed number of threads, but this may change in future Rayon versions (see the num_threads() method for details). In that case, the index for a thread would not change during its lifetime, but thread indices may wind up being reused if threads are terminated and restarted.

fn current_thread_has_pending_tasks(&self) -> Option<bool>

Returns true if the current worker thread currently has "local tasks" pending. This can be useful as part of a heuristic for deciding whether to spawn a new task or execute code on the current thread, particularly in breadth-first schedulers. However, keep in mind that this is an inherently racy check, as other worker threads may be actively "stealing" tasks from our local deque.

Background: Rayon's uses a work-stealing scheduler. The key idea is that each thread has its own deque of tasks. Whenever a new task is spawned -- whether through join(), Scope::spawn(), or some other means -- that new task is pushed onto the thread's local deque. Worker threads have a preference for executing their own tasks; if however they run out of tasks, they will go try to "steal" tasks from other threads. This function therefore has an inherent race with other active worker threads, which may be removing items from the local deque.

fn join<A, B, RA, RB>(&self, oper_a: A, oper_b: B) -> (RA, RB)
where
    A: FnOnce() -> RA + Send,
    B: FnOnce() -> RB + Send,
    RA: Send,
    RB: Send,

Execute oper_a and oper_b in the thread pool and return the results. Equivalent to self.install(|| join(oper_a, oper_b)).

fn scope<'scope, OP, R>(&self, op: OP) -> R
where
    OP: FnOnce(&Scope<'scope>) -> R + Send,
    R: Send,

Creates a scope that executes within this thread pool. Equivalent to self.install(|| scope(...)).

See also: the scope() function.

fn scope_fifo<'scope, OP, R>(&self, op: OP) -> R
where
    OP: FnOnce(&ScopeFifo<'scope>) -> R + Send,
    R: Send,

Creates a scope that executes within this thread pool. Spawns from the same thread are prioritized in relative FIFO order. Equivalent to self.install(|| scope_fifo(...)).

See also: the scope_fifo() function.

fn in_place_scope<'scope, OP, R>(&self, op: OP) -> R
where
    OP: FnOnce(&Scope<'scope>) -> R,

Creates a scope that spawns work into this thread pool.

See also: the in_place_scope() function.

fn in_place_scope_fifo<'scope, OP, R>(&self, op: OP) -> R
where
    OP: FnOnce(&ScopeFifo<'scope>) -> R,

Creates a scope that spawns work into this thread pool in FIFO order.

See also: the in_place_scope_fifo() function.

fn spawn<OP>(&self, op: OP)
where
    OP: FnOnce() + Send + 'static,

Spawns an asynchronous task in this thread pool. This task will run in the implicit, global scope, which means that it may outlast the current stack frame -- therefore, it cannot capture any references onto the stack (you will likely need a move closure).

See also: the spawn() function defined on scopes.

fn spawn_fifo<OP>(&self, op: OP)
where
    OP: FnOnce() + Send + 'static,

Spawns an asynchronous task in this thread pool. This task will run in the implicit, global scope, which means that it may outlast the current stack frame -- therefore, it cannot capture any references onto the stack (you will likely need a move closure).

See also: the spawn_fifo() function defined on scopes.

fn spawn_broadcast<OP>(&self, op: OP)
where
    OP: Fn(BroadcastContext<'_>) + Send + Sync + 'static,

Spawns an asynchronous task on every thread in this thread pool. This task will run in the implicit, global scope, which means that it may outlast the current stack frame -- therefore, it cannot capture any references onto the stack (you will likely need a move closure).

fn yield_now(&self) -> Option<Yield>

Cooperatively yields execution to Rayon.

This is similar to the general [yield_now()], but only if the current thread is part of this thread pool.

Returns Some(Yield::Executed) if anything was executed, Some(Yield::Idle) if nothing was available, or None if the current thread is not part this pool.

fn yield_local(&self) -> Option<Yield>

Cooperatively yields execution to local Rayon work.

This is similar to the general [yield_local()], but only if the current thread is part of this thread pool.

Returns Some(Yield::Executed) if anything was executed, Some(Yield::Idle) if nothing was available, or None if the current thread is not part this pool.