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When a task scope produces <= 1 task to run, run it on the calling thread immediately. (#932)

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While generally speaking the calling thread would have picked up the task first anyways, I don't think it makes much sense usually to block the calling thread until another thread wakes and does the work.
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Philip Degarmo 2020-11-27 12:14:44 -08:00 committed by GitHub
parent 7d4cb70d92
commit ec8fd57c45
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1 changed files with 39 additions and 33 deletions
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72
crates/bevy_tasks/src/task_pool.rs
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@ -167,44 +167,50 @@ impl TaskPool {
let executor: &async_executor::Executor = &*self.executor; let executor: &async_executor::Executor = &*self.executor;
let executor: &'scope async_executor::Executor = unsafe { mem::transmute(executor) }; let executor: &'scope async_executor::Executor = unsafe { mem::transmute(executor) };
let fut = async move { let mut scope = Scope {
let mut scope = Scope { executor,
executor, spawned: Vec::new(),
spawned: Vec::new(),
};
f(&mut scope);
let mut results = Vec::with_capacity(scope.spawned.len());
for task in scope.spawned {
results.push(task.await);
}
results
}; };
// Pin the future on the stack. f(&mut scope);
pin!(fut);
// SAFETY: This function blocks until all futures complete, so we do not read/write the if scope.spawned.is_empty() {
// data from futures outside of the 'scope lifetime. However, rust has no way of knowing Vec::default()
// this so we must convert to 'static here to appease the compiler as it is unable to } else if scope.spawned.len() == 1 {
// validate safety. vec![future::block_on(&mut scope.spawned[0])]
let fut: Pin<&mut (dyn Future<Output = Vec<T>> + Send)> = fut; } else {
let fut: Pin<&'static mut (dyn Future<Output = Vec<T>> + Send + 'static)> = let fut = async move {
unsafe { mem::transmute(fut) }; let mut results = Vec::with_capacity(scope.spawned.len());
for task in scope.spawned {
results.push(task.await);
}
// The thread that calls scope() will participate in driving tasks in the pool forward results
// until the tasks that are spawned by this scope() call complete. (If the caller of scope() };
// happens to be a thread in this thread pool, and we only have one thread in the pool, then
// simply calling future::block_on(spawned) would deadlock.) // Pin the future on the stack.
let mut spawned = self.executor.spawn(fut); pin!(fut);
loop {
if let Some(result) = future::block_on(future::poll_once(&mut spawned)) { // SAFETY: This function blocks until all futures complete, so we do not read/write the
break result; // data from futures outside of the 'scope lifetime. However, rust has no way of knowing
// this so we must convert to 'static here to appease the compiler as it is unable to
// validate safety.
let fut: Pin<&mut (dyn Future<Output = Vec<T>> + Send)> = fut;
let fut: Pin<&'static mut (dyn Future<Output = Vec<T>> + Send + 'static)> =
unsafe { mem::transmute(fut) };
// The thread that calls scope() will participate in driving tasks in the pool forward
// until the tasks that are spawned by this scope() call complete. (If the caller of scope()
// happens to be a thread in this thread pool, and we only have one thread in the pool, then
// simply calling future::block_on(spawned) would deadlock.)
let mut spawned = self.executor.spawn(fut);
loop {
if let Some(result) = future::block_on(future::poll_once(&mut spawned)) {
break result;
}
self.executor.try_tick();
} }
self.executor.try_tick();
} }
} }