Fix racy GetCategory with trace_event

See racy trace_event: http://crbug.com/1091723 The trace event macros were racy because of this code: INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(...) The macro is using a static variable which is not thread-safe. The design of tracing was racy (by design) and rely on the fact that addTraceEvent(...) is threadsafe internally via TraceLog::lock_ This CL is replacing the static variable with a scope (C++11) pattern. The static variable is guaranted (C++) to be atomic and it is implemented efficiently. see: §6.7 [stmt.dcl] p4 " If control enters the declaration concurrently while the variable is being initialized, the concurrent execution shall wait for completion of the initialization. " Bug to track follow-up migration: http://anglebug.com/4702 Bug: chromium:1091259, chromium:1091723 Change-Id: If67b501e6e826ccf603eb2349c3f0aa6272c9a52 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2233410 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>

Fix racy GetCategory with trace_event
f8fd9cfb · Etienne Bergeron · Commit Bot · 86a45a1a · f8fd9cfb
Commit f8fd9cfb authored Jun 09, 2020 by Etienne Bergeron Committed by Commit Bot Jun 09, 2020
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trace_event.h src/third_party/trace_event/trace_event.h +3 -4

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--- a/src/third_party/trace_event/trace_event.h
+++ b/src/third_party/trace_event/trace_event.h
@@ -454,10 +454,9 @@
 #define INTERNALTRACEEVENTUID(name_prefix) INTERNAL_TRACE_EVENT_UID2(name_prefix, __LINE__)
 // Implementation detail: internal macro to create static category.
-#define INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(platform, category)    \
+#define INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(platform, category) \
-    static const unsigned char *INTERNALTRACEEVENTUID(catstatic) = 0; \
+    static const unsigned char *INTERNALTRACEEVENTUID(catstatic) = \
-    if (!INTERNALTRACEEVENTUID(catstatic))                            \
+        TRACE_EVENT_API_GET_CATEGORY_ENABLED(platform, category);
-        INTERNALTRACEEVENTUID(catstatic) = TRACE_EVENT_API_GET_CATEGORY_ENABLED(platform, category);
 // Implementation detail: internal macro to create static category and add
 // event if the category is enabled.