Refactor monotonic time code to avoid duplication.

Merge the monotonic clock source detection in
qeventdispatcher_unix.cpp with that in qcore_unix.cpp. As discussed
with Thiago, we're also removing older compat code at the same time
(spinning on select() when we think it woke up early).

Reviewed-by: Thiago

4 files changed, 60 insertions, 114 deletions

diff --git a/src/corelib/kernel/qcore_unix.cpp b/src/corelib/kernel/qcore_unix.cpp
index c5b0fc7..6ef56fd 100644
--- a/src/corelib/kernel/qcore_unix.cpp
+++ b/src/corelib/kernel/qcore_unix.cpp
@@ -55,37 +55,72 @@
 
 QT_BEGIN_NAMESPACE
 
-static inline timeval gettime()
+bool qt_gettime_is_monotonic()
 {
-    timeval tv;
-#ifndef QT_NO_CLOCK_MONOTONIC
-    // use the monotonic clock
-    static volatile bool monotonicClockDisabled = false;
-    struct timespec ts;
-    if (!monotonicClockDisabled) {
-        if (clock_gettime(CLOCK_MONOTONIC, &ts) == -1) {
-            monotonicClockDisabled = true;
-        } else {
-            tv.tv_sec = ts.tv_sec;
-            tv.tv_usec = ts.tv_nsec / 1000;
-            return tv;
-        }
+#if (_POSIX_MONOTONIC_CLOCK-0 > 0) || defined(Q_OS_MAC)
+    return true;
+#else
+    static int returnValue = 0;
+
+    if (returnValue == 0) {
+#  if (_POSIX_MONOTONIC_CLOCK-0 < 0)
+        returnValue = -1;
+#  elif (_POSIX_MONOTONIC_CLOCK == 0)
+        // detect if the system support monotonic timers
+        long x = sysconf(_SC_MONOTONIC_CLOCK);
+        returnValue = (x >= 200112L) ? 1 : -1;
+#  endif
     }
+
+    return returnValue != -1;
 #endif
+}
+
+timeval qt_gettime()
+{
+    timeval tv;
+#if defined(Q_OS_MAC)
+    static mach_timebase_info_data_t info = {0,0};
+    if (info.denom == 0)
+        mach_timebase_info(&info);
+
+    uint64_t cpu_time = mach_absolute_time();
+    uint64_t nsecs = cpu_time * (info.numer / info.denom);
+    tv.tv_sec = nsecs * 1e-9;
+    tv.tv_usec = nsecs * 1e-3 - (t.tv_sec * 1e6);
+    return tv;
+#elif (_POSIX_MONOTONIC_CLOCK-0 > 0)
+    timespec ts;
+    clock_gettime(CLOCK_MONOTONIC, &ts);
+    tv.tv_sec = ts.tv_sec;
+    tv.tv_usec = ts.tv_nsec / 1000;
+    return tv;
+#else
+#  if !defined(QT_NO_CLOCK_MONOTONIC) && !defined(QT_BOOTSTRAPPED)
+    if (qt_gettime_is_monotonic()) {
+        timespec ts;
+        clock_gettime(CLOCK_MONOTONIC, &ts);
+        tv.tv_sec = ts.tv_sec;
+        tv.tv_usec = ts.tv_nsec / 1000;
+        return tv;
+    }
+#  endif
     // use gettimeofday
     ::gettimeofday(&tv, 0);
     return tv;
+#endif
 }
 
 static inline bool time_update(struct timeval *tv, const struct timeval &start,
                                const struct timeval &timeout)
 {
-    struct timeval now = gettime();
-    if (now < start) {
-        // clock reset, give up
+    if (!qt_gettime_is_monotonic()) {
+        // we cannot recalculate the timeout without a monotonic clock as the time may have changed
         return false;
     }
 
+    // clock source is monotonic, so we can recalculate how much timeout is left
+    struct timeval now = qt_gettime();
     *tv = timeout + start - now;
     return true;
 }
@@ -100,7 +135,7 @@ int qt_safe_select(int nfds, fd_set *fdread, fd_set *fdwrite, fd_set *fdexcept,
         return ret;
     }
 
-    timeval start = gettime();
+    timeval start = qt_gettime();
     timeval timeout = *orig_timeout;
 
     // loop and recalculate the timeout as needed
diff --git a/src/corelib/kernel/qcore_unix_p.h b/src/corelib/kernel/qcore_unix_p.h
index dd97841..bffd670 100644
--- a/src/corelib/kernel/qcore_unix_p.h
+++ b/src/corelib/kernel/qcore_unix_p.h
@@ -267,6 +267,8 @@ static inline pid_t qt_safe_waitpid(pid_t pid, int *status, int options)
     return ret;
 }
 
+bool qt_gettime_is_monotonic();
+timeval qt_gettime();
 Q_CORE_EXPORT int qt_safe_select(int nfds, fd_set *fdread, fd_set *fdwrite, fd_set *fdexcept,
                                  const struct timeval *tv);
 
diff --git a/src/corelib/kernel/qeventdispatcher_unix.cpp b/src/corelib/kernel/qeventdispatcher_unix.cpp
index 2139545..6f1256b 100644
--- a/src/corelib/kernel/qeventdispatcher_unix.cpp
+++ b/src/corelib/kernel/qeventdispatcher_unix.cpp
@@ -67,25 +67,6 @@ QT_BEGIN_NAMESPACE
 
 Q_CORE_EXPORT bool qt_disable_lowpriority_timers=false;
 
-// check for _POSIX_MONOTONIC_CLOCK support
-static bool supportsMonotonicClock()
-{
-    bool returnValue;
-
-#if (_POSIX_MONOTONIC_CLOCK-0 <= 0) && !defined(Q_OS_MAC)
-    returnValue = false;
-#  if (_POSIX_MONOTONIC_CLOCK == 0)
-    // detect if the system support monotonic timers
-    long x = sysconf(_SC_MONOTONIC_CLOCK);
-    returnValue = x >= 200112L;
-#  endif
-#else
-    returnValue = true;
-#endif
-
-    return returnValue;
-}
-
 /*****************************************************************************
  UNIX signal handling
  *****************************************************************************/
@@ -281,12 +262,11 @@ int QEventDispatcherUNIXPrivate::doSelect(QEventLoop::ProcessEventsFlags flags,
  */
 
 QTimerInfoList::QTimerInfoList()
-    : useMonotonicTimers(supportsMonotonicClock())
 {
-    getTime(currentTime);
+    currentTime = qt_gettime();
 
 #if (_POSIX_MONOTONIC_CLOCK-0 <= 0) && !defined(Q_OS_MAC)
-    if (!useMonotonicTimers) {
+    if (!qt_gettime_is_monotonic()) {
         // not using monotonic timers, initialize the timeChanged() machinery
         previousTime = currentTime;
 
@@ -309,8 +289,7 @@ QTimerInfoList::QTimerInfoList()
 
 timeval QTimerInfoList::updateCurrentTime()
 {
-    getTime(currentTime);
-    return currentTime;
+    return (currentTime = qt_gettime());
 }
 
 #if ((_POSIX_MONOTONIC_CLOCK-0 <= 0) && !defined(Q_OS_MAC)) || defined(QT_BOOTSTRAPPED)
@@ -364,38 +343,9 @@ bool QTimerInfoList::timeChanged(timeval *delta)
     return elapsedTimeTicks < ((qAbs(*delta) - tickGranularity) * 10);
 }
 
-void QTimerInfoList::getTime(timeval &t)
-{
-#if !defined(QT_NO_CLOCK_MONOTONIC) && !defined(QT_BOOTSTRAPPED)
-    if (useMonotonicTimers) {
-        timespec ts;
-        clock_gettime(CLOCK_MONOTONIC, &ts);
-        t.tv_sec = ts.tv_sec;
-        t.tv_usec = ts.tv_nsec / 1000;
-        return;
-    }
-#endif
-
-    gettimeofday(&t, 0);
-    // NTP-related fix
-    while (t.tv_usec >= 1000000l) {
-        t.tv_usec -= 1000000l;
-        ++t.tv_sec;
-    }
-    while (t.tv_usec < 0l) {
-        if (t.tv_sec > 0l) {
-            t.tv_usec += 1000000l;
-            --t.tv_sec;
-        } else {
-            t.tv_usec = 0l;
-            break;
-        }
-    }
-}
-
 void QTimerInfoList::repairTimersIfNeeded()
 {
-    if (useMonotonicTimers)
+    if (qt_gettime_is_monotonic())
         return;
     timeval delta;
     if (timeChanged(&delta))
@@ -404,25 +354,6 @@ void QTimerInfoList::repairTimersIfNeeded()
 
 #else // !(_POSIX_MONOTONIC_CLOCK-0 <= 0) && !defined(QT_BOOTSTRAPPED)
 
-void QTimerInfoList::getTime(timeval &t)
-{
-#if defined(Q_OS_MAC)
-    static mach_timebase_info_data_t info = {0,0};
-    if (info.denom == 0)
-        mach_timebase_info(&info);
-
-    uint64_t cpu_time = mach_absolute_time();
-    uint64_t nsecs = cpu_time * (info.numer / info.denom);
-    t.tv_sec = nsecs * 1e-9;
-    t.tv_usec = nsecs * 1e-3 - (t.tv_sec * 1e6);
-#else
-    timespec ts;
-    clock_gettime(CLOCK_MONOTONIC, &ts);
-    t.tv_sec = ts.tv_sec;
-    t.tv_usec = ts.tv_nsec / 1000;
-#endif
-}
-
 void QTimerInfoList::repairTimersIfNeeded()
 {
 }
@@ -648,25 +579,7 @@ QEventDispatcherUNIX::~QEventDispatcherUNIX()
 int QEventDispatcherUNIX::select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
                                  timeval *timeout)
 {
-    Q_D(QEventDispatcherUNIX);
-    if (timeout && d->timerList.useMonotonicTimers) {
-        // handle the case where select returns with a timeout, too
-        // soon.
-        timeval tvStart = d->timerList.currentTime;
-        timeval tvCurrent = tvStart;
-        timeval originalTimeout = *timeout;
-
-        int nsel;
-        do {
-            timeval tvRest = originalTimeout + tvStart - tvCurrent;
-            nsel = ::select(nfds, readfds, writefds, exceptfds, &tvRest);
-            d->timerList.getTime(tvCurrent);
-        } while (nsel == 0 && (tvCurrent - tvStart) < originalTimeout);
-
-        return nsel;
-    }
-
-    return ::select(nfds, readfds, writefds, exceptfds, timeout);
+    return ::qt_safe_select(nfds, readfds, writefds, exceptfds, timeout);
 }
 
 /*!
diff --git a/src/corelib/kernel/qeventdispatcher_unix_p.h b/src/corelib/kernel/qeventdispatcher_unix_p.h
index 28e7f9b..61d94c9 100644
--- a/src/corelib/kernel/qeventdispatcher_unix_p.h
+++ b/src/corelib/kernel/qeventdispatcher_unix_p.h
@@ -141,10 +141,6 @@ class QTimerInfoList : public QList<QTimerInfo*>
 public:
     QTimerInfoList();
 
-    const bool useMonotonicTimers;
-
-    void getTime(timeval &t);
-
     timeval currentTime;
     timeval updateCurrentTime();