Add ability to retrieve a thread_name given a thread_id.

base/debug/trace_event_impl.cc

Index: base/debug/trace_event_impl.cc
diff --git a/base/debug/trace_event_impl.cc b/base/debug/trace_event_impl.cc
index 07679d1131250fb101401191d02434dc6e59e8b8..82bf10308d8de56e848353c3b794a612f2991d05 100644
--- a/base/debug/trace_event_impl.cc
+++ b/base/debug/trace_event_impl.cc
@@ -10,7 +10,6 @@
 #include "base/debug/leak_annotations.h"
 #include "base/debug/trace_event.h"
 #include "base/format_macros.h"
-#include "base/lazy_instance.h"
 #include "base/memory/singleton.h"
 #include "base/process_util.h"
 #include "base/stl_util.h"
@@ -65,9 +64,8 @@ const int g_category_categories_exhausted = 1;
 const int g_category_metadata = 2;
 int g_category_index = 3; // skip initial 3 categories
 
-// The most-recently captured name of the current thread
-LazyInstance<ThreadLocalPointer<const char> >::Leaky
-    g_current_thread_name = LAZY_INSTANCE_INITIALIZER;
+// The most-recently captured name version of the current thread

[jar (doing other things), 2012/12/14 18:23:07]

Please explain what a "name version" is for a thread.

[dsinclair, 2012/12/14 19:13:46]

Done.

[jar (doing other things), 2012/12/21 00:16:59]

The comment change was helpful, as I now am able to parse that this is the
"version number" that is associated with a "thread name.".

I don't grok why you have a version number at all however.  Can you add that to
the comment?

On 2012/12/14 19:13:46, dsinclair wrote:

[dsinclair, 2012/12/21 16:28:59]

Done.

+uint32 g_current_thread_name_version = 0;
 
 }  // namespace
 
@@ -637,13 +635,15 @@ void TraceLog::AddTraceEvent(char phase,
     int thread_id = static_cast<int>(PlatformThread::CurrentId());
 
     const char* new_name = PlatformThread::GetName();
+    uint32 new_version = PlatformThread::GetVersionForName();
     // Check if the thread name has been set or changed since the previous
     // call (if any), but don't bother if the new name is empty. Note this will
     // not detect a thread name change within the same char* buffer address: we
     // favor common case performance over corner case correctness.
-    if (new_name != g_current_thread_name.Get().Get() &&
+    if (new_version != g_current_thread_name_version &&
         new_name && *new_name) {
-      g_current_thread_name.Get().Set(new_name);
+      g_current_thread_name_version = new_version;
+
       base::hash_map<int, std::string>::iterator existing_name =
           thread_names_.find(thread_id);
       if (existing_name == thread_names_.end()) {