diff options
| -rw-r--r-- | library/std/src/sys/windows/thread_parker.rs | 58 |
1 files changed, 34 insertions, 24 deletions
diff --git a/library/std/src/sys/windows/thread_parker.rs b/library/std/src/sys/windows/thread_parker.rs index 68a060ba32d..7697e6bb3be 100644 --- a/library/std/src/sys/windows/thread_parker.rs +++ b/library/std/src/sys/windows/thread_parker.rs @@ -49,19 +49,26 @@ impl Parker { return; } - loop { - // Wait for something to happen. - if c::WaitOnAddress::is_available() { + if c::WaitOnAddress::is_available() { + loop { + // Wait for something to happen, assuming it's still set to PARKED. c::WaitOnAddress(self.ptr(), &PARKED as *const _ as c::LPVOID, 1, c::INFINITE); - } else { - c::NtWaitForKeyedEvent(keyed_event_handle(), self.ptr(), 0, ptr::null_mut()); - } - // Change NOTIFIED=>EMPTY and return in that case. - if self.state.compare_and_swap(NOTIFIED, EMPTY, Acquire) == NOTIFIED { - return; - } else { - // Spurious wake up. We loop to try again. + // Change NOTIFIED=>EMPTY but leave PARKED alone. + if self.state.compare_and_swap(NOTIFIED, EMPTY, Acquire) == NOTIFIED { + // Actually woken up by unpark(). + return; + } else { + // Spurious wake up. We loop to try again. + } } + } else { + // Wait for unpark() to produce this event. + c::NtWaitForKeyedEvent(keyed_event_handle(), self.ptr(), 0, ptr::null_mut()); + // Set the state back to EMPTY (from either PARKED or NOTIFIED). + // Note that we don't just write EMPTY, but use swap() to also + // include a acquire-ordered read to synchronize with unpark()'s + // release-ordered write. + self.state.swap(EMPTY, Acquire); } } @@ -77,9 +84,12 @@ impl Parker { if c::WaitOnAddress::is_available() { // Wait for something to happen, assuming it's still set to PARKED. c::WaitOnAddress(self.ptr(), &PARKED as *const _ as c::LPVOID, 1, dur2timeout(timeout)); - // Change NOTIFIED=>EMPTY and return in that case. + // Set the state back to EMPTY (from either PARKED or NOTIFIED). + // Note that we don't just write EMPTY, but use swap() to also + // include a acquire-ordered read to synchronize with unpark()'s + // release-ordered write. if self.state.swap(EMPTY, Acquire) == NOTIFIED { - return; + // Actually woken up by unpark(). } else { // Timeout or spurious wake up. // We return either way, because we can't easily tell if it was the @@ -97,17 +107,17 @@ impl Parker { }; // Wait for unpark() to produce this event. - if c::NtWaitForKeyedEvent(handle, self.ptr(), 0, &mut timeout) == c::STATUS_SUCCESS { - // Awoken by another thread. - self.state.swap(EMPTY, Acquire); - } else { - // Not awoken by another thread (spurious or timeout). - if self.state.swap(EMPTY, Acquire) == NOTIFIED { - // If the state is NOTIFIED, we *just* missed an unpark(), - // which is now waiting for us to wait for it. - // Wait for it to consume the event and unblock it. - c::NtWaitForKeyedEvent(handle, self.ptr(), 0, ptr::null_mut()); - } + let unparked = c::NtWaitForKeyedEvent(handle, self.ptr(), 0, &mut timeout) == c::STATUS_SUCCESS; + + // Set the state back to EMPTY (from either PARKED or NOTIFIED). + let prev_state = self.state.swap(EMPTY, Acquire); + + if !unparked && prev_state == NOTIFIED { + // We were awoken by a timeout, not by unpark(), but the state + // was set to NOTIFIED, which means we *just* missed an + // unpark(), which is now blocked on us to wait for it. + // Wait for it to consume the event and unblock that thread. + c::NtWaitForKeyedEvent(handle, self.ptr(), 0, ptr::null_mut()); } } } |