Bug 1328408 - make Sampler::GetRegisteredThreads not copy the registered threads list; r=mstange

We call GetRegisteredThreads repeatedly on the sampler thread whenever
the profiler is active; there's no reason to have it churn memory.

tools/profiler/core/platform-linux.cc

@@ -317,7 +317,7 @@ static void* SignalSender(void* arg) {
 
     if (!SamplerRegistry::sampler->IsPaused()) {
       ::MutexAutoLock lock(*Sampler::sRegisteredThreadsMutex);
-      std::vector<ThreadInfo*> threads =
+      const std::vector<ThreadInfo*>& threads =
         SamplerRegistry::sampler->GetRegisteredThreads();
 
       bool isFirstProfiledThread = true;

tools/profiler/core/platform-macos.cc

@@ -211,7 +211,7 @@ class SamplerThread : public Thread {
       SamplerRegistry::sampler->DeleteExpiredMarkers();
       if (!SamplerRegistry::sampler->IsPaused()) {
         ::MutexAutoLock lock(*Sampler::sRegisteredThreadsMutex);
-        std::vector<ThreadInfo*> threads =
+        const std::vector<ThreadInfo*>& threads =
           SamplerRegistry::sampler->GetRegisteredThreads();
         bool isFirstProfiledThread = true;
         for (uint32_t i = 0; i < threads.size(); i++) {

tools/profiler/core/platform-win32.cc

@@ -129,7 +129,7 @@ class SamplerThread : public Thread {
 
       if (!sampler_->IsPaused()) {
         ::MutexAutoLock lock(*Sampler::sRegisteredThreadsMutex);
-        std::vector<ThreadInfo*> threads =
+        const std::vector<ThreadInfo*>& threads =
           sampler_->GetRegisteredThreads();
         bool isFirstProfiledThread = true;
         for (uint32_t i = 0; i < threads.size(); i++) {

tools/profiler/core/platform.cpp

@@ -878,7 +878,7 @@ void mozilla_sampler_start(int aProfileEntries, double aInterval,
   t->Start();
   if (t->ProfileJS() || t->InPrivacyMode()) {
       ::MutexAutoLock lock(*Sampler::sRegisteredThreadsMutex);
-      std::vector<ThreadInfo*> threads = t->GetRegisteredThreads();
+      const std::vector<ThreadInfo*>& threads = t->GetRegisteredThreads();
 
       for (uint32_t i = 0; i < threads.size(); i++) {
         ThreadInfo* info = threads[i];

tools/profiler/core/platform.h

@@ -379,7 +379,7 @@ class Sampler {
   static pthread_t GetProfiledThread(PlatformData*);
 #endif
 
-  static std::vector<ThreadInfo*> GetRegisteredThreads() {
+  static const std::vector<ThreadInfo*>& GetRegisteredThreads() {
     return *sRegisteredThreads;
   }