Title: [225523] trunk/Source/WTF
- Revision
- 225523
- Author
- utatane....@gmail.com
- Date
- 2017-12-05 09:28:14 -0800 (Tue, 05 Dec 2017)
Log Message
[WTF] Use m_suspendCount instead of m_suspended flag in Thread
https://bugs.webkit.org/show_bug.cgi?id=180427
Reviewed by Carlos Garcia Campos.
When resuming the thread, signal handler is reinvoked once before `sigsuspend` is resumed.
But this handler should not do anything since it is just a signal for `sigsuspend`.
Previously, we use m_suspenedd flag to distinguish between suspending and resuming signal
handler invocations.
But this additional m_suspended flag is not necessary since we can use m_suspendCount instead.
This patch drops m_suspended and use m_suspendCount. Since semaphore operations emit full memory
barrier, m_suspendCount is loaded and stored as we expect.
* wtf/Threading.h:
* wtf/ThreadingPthreads.cpp:
(WTF::Thread::signalHandlerSuspendResume):
(WTF::Thread::suspend):
(WTF::Thread::resume):
Modified Paths
Diff
Modified: trunk/Source/WTF/ChangeLog (225522 => 225523)
--- trunk/Source/WTF/ChangeLog 2017-12-05 16:21:16 UTC (rev 225522)
+++ trunk/Source/WTF/ChangeLog 2017-12-05 17:28:14 UTC (rev 225523)
@@ -1,3 +1,25 @@
+2017-12-05 Yusuke Suzuki <utatane....@gmail.com>
+
+ [WTF] Use m_suspendCount instead of m_suspended flag in Thread
+ https://bugs.webkit.org/show_bug.cgi?id=180427
+
+ Reviewed by Carlos Garcia Campos.
+
+ When resuming the thread, signal handler is reinvoked once before `sigsuspend` is resumed.
+ But this handler should not do anything since it is just a signal for `sigsuspend`.
+ Previously, we use m_suspenedd flag to distinguish between suspending and resuming signal
+ handler invocations.
+
+ But this additional m_suspended flag is not necessary since we can use m_suspendCount instead.
+ This patch drops m_suspended and use m_suspendCount. Since semaphore operations emit full memory
+ barrier, m_suspendCount is loaded and stored as we expect.
+
+ * wtf/Threading.h:
+ * wtf/ThreadingPthreads.cpp:
+ (WTF::Thread::signalHandlerSuspendResume):
+ (WTF::Thread::suspend):
+ (WTF::Thread::resume):
+
2017-12-04 Simon Fraser <simon.fra...@apple.com>
Minor DisplayRefreshMonitor-related cleanup
Modified: trunk/Source/WTF/wtf/Threading.h (225522 => 225523)
--- trunk/Source/WTF/wtf/Threading.h 2017-12-05 16:21:16 UTC (rev 225522)
+++ trunk/Source/WTF/wtf/Threading.h 2017-12-05 17:28:14 UTC (rev 225523)
@@ -288,7 +288,6 @@
#elif USE(PTHREADS)
PlatformRegisters* m_platformRegisters { nullptr };
unsigned m_suspendCount { 0 };
- std::atomic<bool> m_suspended { false };
#endif
AtomicStringTable* m_currentAtomicStringTable { nullptr };
Modified: trunk/Source/WTF/wtf/ThreadingPthreads.cpp (225522 => 225523)
--- trunk/Source/WTF/wtf/ThreadingPthreads.cpp 2017-12-05 16:21:16 UTC (rev 225522)
+++ trunk/Source/WTF/wtf/ThreadingPthreads.cpp 2017-12-05 17:28:14 UTC (rev 225523)
@@ -144,10 +144,10 @@
void Thread::signalHandlerSuspendResume(int, siginfo_t*, void* ucontext)
{
- // Touching thread local atomic types from signal handlers is allowed.
+ // Touching a global variable atomic types from signal handlers is allowed.
Thread* thread = targetThread.load();
- if (thread->m_suspended.load(std::memory_order_acquire)) {
+ if (thread->m_suspendCount) {
// This is signal handler invocation that is intended to be used to resume sigsuspend.
// So this handler invocation itself should not process.
//
@@ -350,14 +350,12 @@
if (!m_suspendCount) {
// Ideally, we would like to use pthread_sigqueue. It allows us to pass the argument to the signal handler.
// But it can be used in a few platforms, like Linux.
- // Instead, we use Thread* stored in the thread local storage to pass it to the signal handler.
+ // Instead, we use Thread* stored in a global variable to pass it to the signal handler.
targetThread.store(this);
int result = pthread_kill(m_handle, SigThreadSuspendResume);
if (result)
return makeUnexpected(result);
globalSemaphoreForSuspendResume->wait();
- // Release barrier ensures that this operation is always executed after all the above processing is done.
- m_suspended.store(true, std::memory_order_release);
}
++m_suspendCount;
return { };
@@ -377,14 +375,12 @@
// There are several ways to distinguish the handler invocation for suspend and resume.
// 1. Use different signal numbers. And check the signal number in the handler.
// 2. Use some arguments to distinguish suspend and resume in the handler. If pthread_sigqueue can be used, we can take this.
- // 3. Use thread local storage with atomic variables in the signal handler.
- // In this implementaiton, we take (3). suspended flag is used to distinguish it.
+ // 3. Use thread's flag.
+ // In this implementaiton, we take (3). m_suspendCount is used to distinguish it.
targetThread.store(this);
if (pthread_kill(m_handle, SigThreadSuspendResume) == ESRCH)
return;
globalSemaphoreForSuspendResume->wait();
- // Release barrier ensures that this operation is always executed after all the above processing is done.
- m_suspended.store(false, std::memory_order_release);
}
--m_suspendCount;
#endif
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