QSemaphore: fix regression when the timeout < 0

The issue was introduced by eaee1209f0ead5be786e81db8aee604ccfea85b0, so
it affected only 5.9.2.

[ChangeLog][QtCore][QSemaphore] Fixed a regression that would make
tryAcquire() not to wait forever if the timeout was a negative
value. Note: new code is advised to only use -1 to indicate "forever",
as some other functions taking timeout periods do not accept other
values.

Task-number: QTBUG-64413
Change-Id: I57a1bd6e0c194530b732fffd14f58fce60d5dfc9
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 5 insertions, 3 deletions

diff --git a/src/corelib/thread/qsemaphore.cpp b/src/corelib/thread/qsemaphore.cpp
index ce0c1c91df..f63a08774c 100644
--- a/src/corelib/thread/qsemaphore.cpp
+++ b/src/corelib/thread/qsemaphore.cpp
@@ -214,13 +214,15 @@ bool QSemaphore::tryAcquire(int n)
 bool QSemaphore::tryAcquire(int n, int timeout)
 {
     Q_ASSERT_X(n >= 0, "QSemaphore::tryAcquire", "parameter 'n' must be non-negative");
-    if (timeout < 0)
-        return tryAcquire(n);
+
+    // We're documented to accept any negative value as "forever"
+    // but QDeadlineTimer only accepts -1.
+    timeout = qMax(timeout, -1);
 
     QDeadlineTimer timer(timeout);
     QMutexLocker locker(&d->mutex);
     qint64 remainingTime = timer.remainingTime();
-    while (n > d->avail && remainingTime > 0) {
+    while (n > d->avail && remainingTime != 0) {
         if (!d->cond.wait(locker.mutex(), remainingTime))
             return false;
         remainingTime = timer.remainingTime();