Add ability to retrieve a thread_name given a thread_id.

base/threading/thread_id_name_manager.cc

Index: base/threading/thread_id_name_manager.cc
diff --git a/base/threading/thread_id_name_manager.cc b/base/threading/thread_id_name_manager.cc
new file mode 100644
index 0000000000000000000000000000000000000000..6f429c2aa3c7518a643aec14aa66d17b86b3b60e
--- /dev/null
+++ b/base/threading/thread_id_name_manager.cc
@@ -0,0 +1,42 @@
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/threading/thread_id_name_manager.h"
+
+#include "base/memory/singleton.h"
+
+namespace base {
+
+ThreadIdNameManager::ThreadIdNameManager() {
+}
+
+ThreadIdNameManager::~ThreadIdNameManager() {
+}
+
+ThreadIdNameManager* ThreadIdNameManager::GetInstance() {
+  return Singleton<ThreadIdNameManager,
+      LeakySingletonTraits<ThreadIdNameManager> >::get();
+}
+
+const char* ThreadIdNameManager::GetNameForId(PlatformThreadId id) {
+  base::AutoLock locked(lock_);
+
+  std::map<PlatformThreadId, const char*>::const_iterator it;
+  it = id_to_name_.find(id);
+  if (it == id_to_name_.end())
+    return NULL;
+  return it->second;
+}
+
+void ThreadIdNameManager::SetNameForId(PlatformThreadId id, const char* name) {
+  base::AutoLock locked(lock_);
+  id_to_name_[id] = name;

[jar (doing other things), 2012/12/06 20:54:37]

nit: can/should we have a DCHECK here to verify that it is not set twice?

[dsinclair, 2012/12/10 16:24:36]

It seems that being able to SetName multiple times is expected behaviour. There
is a unittest in the trace_event code which tests that exact thing.

+}
+
+void ThreadIdNameManager::RemoveNameForId(PlatformThreadId id) {
+  base::AutoLock locked(lock_);
+  id_to_name_.erase(id);

[jar (doing other things), 2012/12/06 20:54:37]

nit: can/should we have a DCHECK here to verify that it was indeed set
previously (i.e., that we didn't miss a hook to set it?)  Or are there worker
threads that just don't get set?

[dsinclair, 2012/12/10 16:24:36]

It's possible the name wouldn't be set, but in that case we'd also have a
kInvalidThreadId pass for id. So, I can handle that case and add the DCHECK.

+}
+
+}  // namespace base