1berry/qtbase
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Simplify the futex lock loop: no need for nested while

Browse Source 
Once we enter the inner loop, we never exit it except to return from
the lockInternal() function, so the rest is never executed again.

As a consequence of this, we won't try to fastTryLock() twice per
mutex. Therefore, for a non-recursive mutex, if lockInternal() is
entered, we'll definitely need to use futexes.

Change-Id: Ice617ed27449c1fbdc112a159a86cd0660125e13
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
This commit is contained in:
Thiago Macieira 2012-08-11 14:47:10 +02:00 committed by Qt by Nokia
parent 30bea611df
commit fc174a3728
1 changed files with 23 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

48
src/corelib/thread/qmutex_linux.cpp
View File

@ -126,34 +126,32 @@ bool QBasicMutex::lockInternal(int timeout) Q_DECL_NOTHROW
if (timeout >= 1) if (timeout >= 1)
elapsedTimer.start(); elapsedTimer.start();
while (!fastTryLock()) { // the mutex is locked already, set a bit indicating we're waiting
d = d_ptr.load(); while (d_ptr.fetchAndStoreAcquire(dummyFutexValue()) != 0) {
struct timespec ts, *pts = 0;
if (!d) // if d is 0, the mutex is unlocked if (timeout >= 1) {
continue; // recalculate the timeout
// the mutex is locked already, set a bit indicating we're waiting qint64 xtimeout = qint64(timeout) * 1000 * 1000;
while (d_ptr.fetchAndStoreAcquire(dummyFutexValue()) != 0) { xtimeout -= elapsedTimer.nsecsElapsed();
struct timespec ts, *pts = 0; if (xtimeout <= 0) {
if (timeout >= 1) { // timer expired after we returned
// recalculate the timeout
qint64 xtimeout = qint64(timeout) * 1000 * 1000;
xtimeout -= elapsedTimer.nsecsElapsed();
if (xtimeout <= 0) {
// timer expired after we returned
return false;
}
ts.tv_sec = xtimeout / Q_INT64_C(1000) / 1000 / 1000;
ts.tv_nsec = xtimeout % (Q_INT64_C(1000) * 1000 * 1000);
pts = &ts;
}
// successfully set the waiting bit, now sleep
int r = _q_futex(&d_ptr, FUTEX_WAIT, quintptr(dummyFutexValue()), pts);
if (r != 0 && errno == ETIMEDOUT)
return false; return false;
}
ts.tv_sec = xtimeout / Q_INT64_C(1000) / 1000 / 1000;
ts.tv_nsec = xtimeout % (Q_INT64_C(1000) * 1000 * 1000);
pts = &ts;
} }
return true;
// successfully set the waiting bit, now sleep
int r = _q_futex(&d_ptr, FUTEX_WAIT, quintptr(dummyFutexValue()), pts);
if (r != 0 && errno == ETIMEDOUT)
return false;
// we got woken up, so try to acquire the mutex
// note we must set to dummyFutexValue because there could be other threads
// also waiting
} }
Q_ASSERT(d_ptr.load()); Q_ASSERT(d_ptr.load());
return true; return true;
} }