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Internals: Avoid pessimistic mutex locking in waitIfStopRequested() (#4272). No functional change intended.

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`stopRequested()` reads only atomic variables. It doesn't need a mutex
to do this.

This function is called in `waitIfStopRequested()`, which in turn
is called before execution of every job, and inside some jobs. With this
change the mutex inside `waitIfStopRequested` needs to be locked only in
very rare cases instead of every time.
This commit is contained in:
Mariusz Glebocki 2023-06-06 01:40:36 +02:00 committed by GitHub
parent 5aa36357f6
commit 186c851695
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GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 5 additions and 10 deletions
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6
src/V3ThreadPool.cpp
View File

@ -68,7 +68,7 @@ void V3ThreadPool::workerJobLoop(int id) VL_MT_SAFE {
return !m_queue.empty() || m_shutdown || m_stopRequested;
});
if (m_shutdown) return; // Terminate if requested
if (stopRequestedStandalone()) { continue; }
if (stopRequested()) { continue; }
// Get the job
UASSERT(!m_queue.empty(), "Job should be available");
@ -115,9 +115,9 @@ void V3ThreadPool::requestExclusiveAccess(const V3ThreadPool::job_t&& exclusiveA
}
}
bool V3ThreadPool::waitIfStopRequested() VL_MT_SAFE {
V3LockGuard stoppedJobLock(m_stoppedJobsMutex);
bool V3ThreadPool::waitIfStopRequested() VL_MT_SAFE VL_EXCLUDES(m_stoppedJobsMutex) {
if (!stopRequested()) return false;
V3LockGuard stoppedJobLock(m_stoppedJobsMutex);
waitStopRequested();
return true;
}

9
src/V3ThreadPool.h
View File

@ -93,7 +93,7 @@ public:
// Check if other thread requested exclusive access to processing,
// if so, it waits for it to complete. Afterwards it is resumed.
// Returns true if request was send and we waited, otherwise false
bool waitIfStopRequested() VL_MT_SAFE;
bool waitIfStopRequested() VL_MT_SAFE VL_EXCLUDES(m_stoppedJobsMutex);
// Waits for future.
// This function can be interupted by exclusive access request.
@ -139,17 +139,12 @@ private:
}
// True when any thread requested exclusive access
bool stopRequested() const VL_REQUIRES(m_stoppedJobsMutex) {
bool stopRequested() const VL_MT_SAFE {
// don't wait if shutdown already requested
if (m_shutdown) return false;
return m_stopRequested;
}
bool stopRequestedStandalone() VL_MT_SAFE_EXCLUDES(m_stoppedJobsMutex) {
const V3LockGuard lock{m_stoppedJobsMutex};
return stopRequested();
}
// Waits until exclusive access job completes its job
void waitStopRequested() VL_REQUIRES(m_stoppedJobsMutex);