Changeset 167263 in webkit

Timestamp:

Apr 14, 2014 1:31:45 PM (10 years ago)

Author:

mark.lam@apple.com

Message:

monotonicallyIncreasingTime() should only initialize its static timebaseInfo once.
<​https://webkit.org/b/131630>

Reviewed by Filip Pizlo.

The current initialization of the static field is not thread safe.

• wtf/CurrentTime.cpp:

(WTF::monotonicallyIncreasingTime):

Location:

trunk/Source/WTF

Files:

• ChangeLog (modified) (1 diff)
• wtf/CurrentTime.cpp (modified) (2 diffs)

trunk/Source/WTF/ChangeLog

@@ +1 @@
+2014-04-14  Mark Lam  <mark.lam@apple.com>
+
+        monotonicallyIncreasingTime() should only initialize its static timebaseInfo once.
+        <https://webkit.org/b/131630>
+
+        Reviewed by Filip Pizlo.
+
+        The current initialization of the static field is not thread safe.
+
+        * wtf/CurrentTime.cpp:
+        (WTF::monotonicallyIncreasingTime):
+
 2014-04-14  Benjamin Poulain  <benjamin@webkit.org>
 

trunk/Source/WTF/wtf/CurrentTime.cpp

@@ -38 +38 @@
 #include <mach/mach.h>
 #include <mach/mach_time.h>
+#include <mutex>
 #include <sys/time.h>
 #elif OS(WINDOWS)
@@ -272 +273 @@
 double monotonicallyIncreasingTime()
 {
-    // Based on listing #2 from Apple QA 1398.
+    // Based on listing #2 from Apple QA 1398, but modified to be thread-safe.
     static mach_timebase_info_data_t timebaseInfo;
-    if (!timebaseInfo.denom) {
+    static std::once_flag initializeTimerOnceFlag;
+    std::call_once(initializeTimerOnceFlag, [] {
         kern_return_t kr = mach_timebase_info(&timebaseInfo);
         ASSERT_UNUSED(kr, kr == KERN_SUCCESS);
-    }
+        ASSERT(timebaseInfo.denom);
+    });
+
     return (mach_absolute_time() * timebaseInfo.numer) / (1.0e9 * timebaseInfo.denom);
 }