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Internals: V3LockGuard: Add constructor for adopting already locked mutex. (#4476)

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This commit is contained in:
Kamil Rakoczy
2023-09-13 13:52:59 -04:00
committed by GitHub
parent 823e0723fb
commit 9fe459c820
5 changed files with 125 additions and 23 deletions
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src/V3ThreadPool.cpp
+68 -14
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@@ -24,13 +24,16 @@
constexpr unsigned int V3ThreadPool::FUTUREWAITFOR_MS;
void V3ThreadPool::resize(unsigned n) VL_MT_UNSAFE VL_EXCLUDES(m_mutex)
VL_EXCLUDES(m_stoppedJobsMutex) {
VL_EXCLUDES(m_stoppedJobsMutex) VL_EXCLUDES(V3MtDisabledLock::instance()) {
// At least one thread (main)
n = std::max(1u, n);
if (n == (m_workers.size() + 1)) { return; }
// This function is not thread-safe and can result in race between threads
UASSERT(V3MutexConfig::s().lockConfig(),
"Mutex config needs to be locked before starting ThreadPool");
{
V3LockGuard lock{m_mutex};
V3LockGuard stoppedJobsLock{m_stoppedJobsMutex};
V3LockGuard lock{m_mutex};
UASSERT(m_queue.empty(), "Resizing busy thread pool");
// Shut down old threads
@@ -38,6 +41,7 @@ void V3ThreadPool::resize(unsigned n) VL_MT_UNSAFE VL_EXCLUDES(m_mutex)
m_stoppedJobs = 0;
m_cv.notify_all();
m_stoppedJobsCV.notify_all();
m_exclusiveAccessThreadCV.notify_all();
}
while (!m_workers.empty()) {
m_workers.front().join();
@@ -53,6 +57,37 @@ void V3ThreadPool::resize(unsigned n) VL_MT_UNSAFE VL_EXCLUDES(m_mutex)
}
}
void V3ThreadPool::suspendMultithreading() VL_MT_SAFE VL_EXCLUDES(m_mutex)
VL_EXCLUDES(m_stoppedJobsMutex) {
V3LockGuard stoppedJobsLock{m_stoppedJobsMutex};
if (!m_workers.empty()) { stopOtherThreads(); }
if (!m_mutex.try_lock()) {
v3fatal("Tried to suspend thread pool when other thread uses it.");
}
V3LockGuard lock{m_mutex, std::adopt_lock_t{}};
UASSERT(m_queue.empty(), "Thread pool has pending jobs");
UASSERT(m_jobsInProgress == 0, "Thread pool has jobs in progress");
m_exclusiveAccess = true;
m_multithreadingSuspended = true;
}
void V3ThreadPool::resumeMultithreading() VL_MT_SAFE VL_EXCLUDES(m_mutex)
VL_EXCLUDES(m_stoppedJobsMutex) {
if (!m_mutex.try_lock()) { v3fatal("Tried to resume thread pool when other thread uses it."); }
{
V3LockGuard lock{m_mutex, std::adopt_lock_t{}};
UASSERT(m_multithreadingSuspended, "Multithreading is not suspended");
m_multithreadingSuspended = false;
m_exclusiveAccess = false;
}
if (!m_workers.empty()) {
V3LockGuard stoppedJobsLock{m_stoppedJobsMutex};
resumeOtherThreads();
}
}
void V3ThreadPool::startWorker(V3ThreadPool* selfThreadp, int id) VL_MT_SAFE {
selfThreadp->workerJobLoop(id);
}
@@ -74,10 +109,14 @@ void V3ThreadPool::workerJobLoop(int id) VL_MT_SAFE {
job = std::move(m_queue.front());
m_queue.pop();
++m_jobsInProgress;
}
// Execute the job
job();
// Note that a context switch can happen here. This means `m_jobsInProgress` could still
// contain old value even after the job promise has been fulfilled.
--m_jobsInProgress;
}
}
@@ -90,25 +129,22 @@ bool V3ThreadPool::waitIfStopRequested() VL_MT_SAFE VL_EXCLUDES(m_stoppedJobsMut
void V3ThreadPool::waitForResumeRequest() VL_REQUIRES(m_stoppedJobsMutex) {
++m_stoppedJobs;
m_stoppedJobsCV.notify_all();
m_stoppedJobsCV.wait(m_stoppedJobsMutex, [&]() VL_REQUIRES(m_stoppedJobsMutex) {
return !m_stopRequested.load();
});
m_exclusiveAccessThreadCV.notify_one();
m_stoppedJobsCV.wait(m_stoppedJobsMutex,
[&]() VL_REQUIRES(m_stoppedJobsMutex) { return !m_stopRequested; });
--m_stoppedJobs;
m_stoppedJobsCV.notify_all();
}
void V3ThreadPool::stopOtherThreads() VL_MT_SAFE_EXCLUDES(m_mutex)
VL_REQUIRES(m_stoppedJobsMutex) {
m_stopRequested = true;
++m_stoppedJobs;
m_stoppedJobsCV.notify_all();
m_cv.notify_all();
m_stoppedJobsCV.wait(m_stoppedJobsMutex, [&]() VL_REQUIRES(m_stoppedJobsMutex) {
// count also the main thread
return m_stoppedJobs == (m_workers.size() + 1);
{
V3LockGuard lock{m_mutex};
m_cv.notify_all();
}
m_exclusiveAccessThreadCV.wait(m_stoppedJobsMutex, [&]() VL_REQUIRES(m_stoppedJobsMutex) {
return m_stoppedJobs == m_workers.size();
});
--m_stoppedJobs;
}
void V3ThreadPool::selfTestMtDisabled() {
@@ -171,7 +207,25 @@ void V3ThreadPool::selfTest() {
{
const V3MtDisabledLockGuard mtDisabler{v3MtDisabledLock()};
selfTestMtDisabled();
{
V3LockGuard lock{V3ThreadPool::s().m_mutex};
UASSERT(V3ThreadPool::s().m_multithreadingSuspended,
"Multithreading should be suspended at this point");
}
}
{
V3LockGuard lock{V3ThreadPool::s().m_mutex};
UASSERT(!V3ThreadPool::s().m_multithreadingSuspended,
"Multithreading should not be suspended at this point");
}
}
V3MtDisabledLock V3MtDisabledLock::s_mtDisabledLock;
void V3MtDisabledLock::lock() VL_ACQUIRE() VL_MT_SAFE {
V3ThreadPool::s().suspendMultithreading();
}
void V3MtDisabledLock::unlock() VL_RELEASE() VL_MT_SAFE {
V3ThreadPool::s().resumeMultithreading();
}