Use leaky lazy instance for master lock in profiler

The master lock is very rarely used, so we can afford
to use a lazy instance of this lock.

r=rtenneti
BUG=104167
Review URL: http://codereview.chromium.org/8567007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@109947 0039d316-1c4b-4281-b951-d872f2087c98

base/tracked_objects.cc

@@ -165,7 +165,9 @@ ThreadData* ThreadData::all_thread_data_list_head_ = NULL;
 ThreadData::ThreadDataPool* ThreadData::unregistered_thread_data_pool_ = NULL;
 
 // static
-base::Lock* ThreadData::list_lock_;
+base::LazyInstance<base::Lock,
+                   base::LeakyLazyInstanceTraits<base::Lock> >
+    ThreadData::list_lock_(base::LINKER_INITIALIZED);
 
 // static
 ThreadData::Status ThreadData::status_ = ThreadData::UNINITIALIZED;
@@ -185,7 +187,7 @@ ThreadData::ThreadData()
       is_a_worker_thread_(true) {
   int thread_number;
   {
-    base::AutoLock lock(*list_lock_);
+    base::AutoLock lock(*list_lock_.Pointer());
     thread_number = ++thread_number_counter_;
   }
   base::StringAppendF(&thread_name_, "WorkerThread-%d", thread_number);
@@ -196,7 +198,7 @@ ThreadData::~ThreadData() {}
 
 void ThreadData::PushToHeadOfList() {
   DCHECK(!next_);
-  base::AutoLock lock(*list_lock_);
+  base::AutoLock lock(*list_lock_.Pointer());
   incarnation_count_for_pool_ = incarnation_counter_;
   next_ = all_thread_data_list_head_;
   all_thread_data_list_head_ = this;
@@ -225,8 +227,9 @@ ThreadData* ThreadData::Get() {
   // We must be a worker thread, since we didn't pre-register.
   ThreadData* worker_thread_data = NULL;
   {
-    base::AutoLock lock(*list_lock_);
-    if (!unregistered_thread_data_pool_->empty()) {
+    base::AutoLock lock(*list_lock_.Pointer());
+    if (unregistered_thread_data_pool_ &&
+        !unregistered_thread_data_pool_->empty()) {
       worker_thread_data =
         const_cast<ThreadData*>(unregistered_thread_data_pool_->top());
       unregistered_thread_data_pool_->pop();
@@ -253,7 +256,7 @@ void ThreadData::OnThreadTermination(void* thread_data) {
 void ThreadData::OnThreadTerminationCleanup() const {
   if (!is_a_worker_thread_)
     return;
-  base::AutoLock lock(*list_lock_);
+  base::AutoLock lock(*list_lock_.Pointer());
   if (incarnation_counter_ != incarnation_count_for_pool_)
     return;  // ThreadData was constructed in an earlier unit test.
 
@@ -261,7 +264,8 @@ void ThreadData::OnThreadTerminationCleanup() const {
   // In that case, the pool might be NULL.  We really should detect this via the
   // incarnation_counter_, but this call is rarely made, so we can afford to
   // code defensively.
-  if (unregistered_thread_data_pool_)
+  if (!unregistered_thread_data_pool_)
+    unregistered_thread_data_pool_ = new ThreadDataPool;
   unregistered_thread_data_pool_->push(this);
 }
 
@@ -535,7 +539,7 @@ void ThreadData::TallyRunInAScopedRegionIfTracking(
 
 // static
 ThreadData* ThreadData::first() {
-  base::AutoLock lock(*list_lock_);
+  base::AutoLock lock(*list_lock_.Pointer());
   return all_thread_data_list_head_;
 }
 
@@ -588,17 +592,9 @@ bool ThreadData::Initialize() {
   if (!tls_index_.initialized())  // Testing may have initialized this.
     tls_index_.Initialize(&ThreadData::OnThreadTermination);
   DCHECK(tls_index_.initialized());
-  ThreadDataPool* pool = new ThreadDataPool;
-  // TODO(jar): A linker initialized spin lock would be much safer than this
-  // allocation, which relies on being called while single threaded.
-  if (!list_lock_)  // In case testing deleted this.
-    list_lock_ = new base::Lock;
   status_ = kInitialStartupState;
 
-  base::AutoLock lock(*list_lock_);
-  DCHECK_EQ(unregistered_thread_data_pool_,
-            reinterpret_cast<ThreadDataPool*>(NULL));
-  unregistered_thread_data_pool_ = pool;
+  base::AutoLock lock(*list_lock_.Pointer());
   ++incarnation_counter_;
   return true;
 }
@@ -644,7 +640,7 @@ void ThreadData::ShutdownSingleThreadedCleanup(bool leak) {
   ThreadData* thread_data_list;
   ThreadDataPool* final_pool;
   {
-    base::AutoLock lock(*list_lock_);
+    base::AutoLock lock(*list_lock_.Pointer());
     thread_data_list = all_thread_data_list_head_;
     all_thread_data_list_head_ = NULL;
     final_pool = unregistered_thread_data_pool_;

base/tracked_objects.h

@@ -12,6 +12,7 @@
 #include <vector>
 
 #include "base/base_export.h"
+#include "base/lazy_instance.h"
 #include "base/location.h"
 #include "base/profiler/tracked_time.h"
 #include "base/time.h"
@@ -432,7 +433,7 @@ class BASE_EXPORT Aggregation: public DeathData {
 //------------------------------------------------------------------------------
 // Comparator is a class that supports the comparison of Snapshot instances.
 // An instance is actually a list of chained Comparitors, that can provide for
-// arbitrary ordering.  The path portion of an about:tracking URL is translated
+// arbitrary ordering.  The path portion of an about:profiler URL is translated
 // into such a chain, which is then used to order Snapshot instances in a
 // vector.  It orders them into groups (for aggregation), and can also order
 // instances within the groups (for detailed rendering of the instances in an
@@ -575,7 +576,7 @@ class BASE_EXPORT ThreadData {
   // This may return NULL if the system is disabled for any reason.
   static ThreadData* Get();
 
-  // For a given (unescaped) about:tracking query, develop resulting HTML, and
+  // For a given (unescaped) about:profiler query, develop resulting HTML, and
   // append to output.
   static void WriteHTML(const std::string& query, std::string* output);
 
@@ -642,7 +643,7 @@ class BASE_EXPORT ThreadData {
   ThreadData* next() const { return next_; }
   // Using our lock, make a copy of the specified maps.  These calls may arrive
   // from non-local threads, and are used to quickly scan data from all threads
-  // in order to build an HTML page for about:tracking.
+  // in order to build an HTML page for about:profiler.
   void SnapshotBirthMap(BirthMap *output) const;
   void SnapshotDeathMap(DeathMap *output) const;
   // -------- end of should be private methods.
@@ -747,7 +748,10 @@ class BASE_EXPORT ThreadData {
   static int incarnation_counter_;
   // Protection for access to all_thread_data_list_head_, and to
   // unregistered_thread_data_pool_.  This lock is leaked at shutdown.
-  static base::Lock* list_lock_;
+  // The lock is very infrequently used, so we can afford to just make a lazy
+  // instance and be safe.
+  static base::LazyInstance<base::Lock,
+    base::LeakyLazyInstanceTraits<base::Lock> > list_lock_;
 
   // Record of what the incarnation_counter_ was when this instance was created.
   // If the incarnation_counter_ has changed, then we avoid pushing into the