Android: fix timed QWaitCondition::wait() on Android >= 5.0.

wait() was always returning immediately, regardless of the timeout
value, due to a timespec comparison from different clock types.
On Android 5.0, qt_gettime() uses the monotonic clock but the wait
condition was using the real time clock.

__pthread_cond_timedwait_relative() is not exported anymore in
Android 5.0, we therefore fall back to pthread_cond_timedwait().
Since the monotonic clock is now available, qt_gettime returns
a time based on it. The wait condition consequently needs
to use the monotonic clock.

Change-Id: Ie7cf909b81107edd7207c3c039b3ec1f5422303f
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@theqtcompany.com>

1 files changed, 13 insertions, 5 deletions

diff --git a/src/corelib/thread/qwaitcondition_unix.cpp b/src/corelib/thread/qwaitcondition_unix.cpp
index 3bcf3202a1..e03187196f 100644
--- a/src/corelib/thread/qwaitcondition_unix.cpp
+++ b/src/corelib/thread/qwaitcondition_unix.cpp
@@ -52,9 +52,12 @@
 QT_BEGIN_NAMESPACE
 
 #ifdef Q_OS_ANDROID
-// Android lacks pthread_condattr_setclock, but it does have a nice function
-// for relative waits. Use weakref so we can determine at runtime whether it is
-// present.
+// pthread_condattr_setclock is available only since Android 5.0. On older versions, there's
+// a private function for relative waits (hidden in 5.0).
+// Use weakref so we can determine at runtime whether each of them is present.
+static int local_condattr_setclock(pthread_condattr_t*, clockid_t)
+__attribute__((weakref("pthread_condattr_setclock")));
+
 static int local_cond_timedwait_relative(pthread_cond_t*, pthread_mutex_t *, const timespec *)
 __attribute__((weakref("__pthread_cond_timedwait_relative")));
 #endif
@@ -70,10 +73,15 @@ void qt_initialize_pthread_cond(pthread_cond_t *cond, const char *where)
     pthread_condattr_t condattr;
 
     pthread_condattr_init(&condattr);
-#if !defined(Q_OS_MAC) && !defined(Q_OS_ANDROID) && (_POSIX_MONOTONIC_CLOCK-0 >= 0)
+#if (_POSIX_MONOTONIC_CLOCK-0 >= 0)
+#if defined(Q_OS_ANDROID)
+    if (local_condattr_setclock && QElapsedTimer::clockType() == QElapsedTimer::MonotonicClock)
+        local_condattr_setclock(&condattr, CLOCK_MONOTONIC);
+#elif !defined(Q_OS_MAC)
     if (QElapsedTimer::clockType() == QElapsedTimer::MonotonicClock)
         pthread_condattr_setclock(&condattr, CLOCK_MONOTONIC);
 #endif
+#endif
     report_error(pthread_cond_init(cond, &condattr), where, "cv init");
     pthread_condattr_destroy(&condattr);
 }
@@ -108,7 +116,7 @@ public:
     {
         timespec ti;
 #ifdef Q_OS_ANDROID
-        if (Q_LIKELY(local_cond_timedwait_relative)) {
+        if (local_cond_timedwait_relative) {
             ti.tv_sec = time / 1000;
             ti.tv_nsec = time % 1000 * Q_UINT64_C(1000) * 1000;
             return local_cond_timedwait_relative(&cond, &mutex, &ti);