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..3b2b9306fd0c18e79a1ea26409349a23e6ea4b5f 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"
@@ -20,6 +19,7 @@
 #include "base/sys_info.h"
 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
 #include "base/threading/platform_thread.h"
+#include "base/threading/thread_id_name_manager.h"
 #include "base/threading/thread_local.h"
 #include "base/time.h"
 #include "base/utf_string_conversions.h"
@@ -65,9 +65,12 @@ 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 version number for the name of the current thread. This is used to
+// decide if the current thread name has changed. We combine all the seen
+// thread names into the output name for the thread. We can't use the pointer
+// as ThreadIdNameManager has a higher chance of giving us the same memory

[jar (doing other things), 2012/12/26 22:41:11]

I still don't get the use case.
I think you're saying that you can't use the optimization of treating the
pointer to the original string as an atom, since the string might be
deallocated/reallocated.  

I can understand that....

so maybe I could see having a unique id for the thread (that is not dependent on
name, or where name is stored).  I wouldn't call that a "version of a name," as
that sounds like a single name has many incarnations (versions).

+// address.
+uint32 g_current_thread_name_version = 0;
 
 }  // namespace
 
@@ -635,15 +638,18 @@ void TraceLog::AddTraceEvent(char phase,
       return;
 
     int thread_id = static_cast<int>(PlatformThread::CurrentId());
+    ThreadIdNameManager* manager = ThreadIdNameManager::GetInstance();
+    const char* new_name = manager->GetNameForId(thread_id);
+    uint32 new_version = manager->GetVersionForId(thread_id);
 
-    const char* new_name = PlatformThread::GetName();
     // 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()) {