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

1 files changed, 53 insertions, 18 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