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rt: reduce an unnecessary lock operation #4436

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Jan 28, 2022
Merged

rt: reduce an unnecessary lock operation #4436

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72 changes: 33 additions & 39 deletions tokio/src/runtime/blocking/pool.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -220,54 +220,48 @@ impl fmt::Debug for BlockingPool {

impl Spawner {
pub(crate) fn spawn(&self, task: Task, rt: &Handle) -> Result<(), ()> {
let shutdown_tx = {
let mut shared = self.inner.shared.lock();
let mut shared = self.inner.shared.lock();

if shared.shutdown {
// Shutdown the task: it's fine to shutdown this task (even if
// mandatory) because it was scheduled after the shutdown of the
// runtime began.
task.task.shutdown();
if shared.shutdown {
// Shutdown the task: it's fine to shutdown this task (even if
// mandatory) because it was scheduled after the shutdown of the
// runtime began.
task.task.shutdown();

// no need to even push this task; it would never get picked up
return Err(());
}
// no need to even push this task; it would never get picked up
return Err(());
}

shared.queue.push_back(task);
shared.queue.push_back(task);

if shared.num_idle == 0 {
// No threads are able to process the task.
if shared.num_idle == 0 {
// No threads are able to process the task.

if shared.num_th == self.inner.thread_cap {
// At max number of threads
None
} else {
shared.num_th += 1;
assert!(shared.shutdown_tx.is_some());
shared.shutdown_tx.clone()
}
if shared.num_th == self.inner.thread_cap {
// At max number of threads
} else {
// Notify an idle worker thread. The notification counter
// is used to count the needed amount of notifications
// exactly. Thread libraries may generate spurious
// wakeups, this counter is used to keep us in a
// consistent state.
shared.num_idle -= 1;
shared.num_notify += 1;
self.inner.condvar.notify_one();
None
}
};

if let Some(shutdown_tx) = shutdown_tx {
let mut shared = self.inner.shared.lock();
shared.num_th += 1;
assert!(shared.shutdown_tx.is_some());
let shutdown_tx = shared.shutdown_tx.clone();

let id = shared.worker_thread_index;
shared.worker_thread_index += 1;
if let Some(shutdown_tx) = shutdown_tx {
let id = shared.worker_thread_index;
shared.worker_thread_index += 1;

let handle = self.spawn_thread(shutdown_tx, rt, id);
let handle = self.spawn_thread(shutdown_tx, rt, id);

shared.worker_threads.insert(id, handle);
shared.worker_threads.insert(id, handle);
}
}
} else {
// Notify an idle worker thread. The notification counter
// is used to count the needed amount of notifications
// exactly. Thread libraries may generate spurious
// wakeups, this counter is used to keep us in a
// consistent state.
shared.num_idle -= 1;
shared.num_notify += 1;
self.inner.condvar.notify_one();
}

Ok(())
Expand Down