Bug 724368 - Expose the maximum number of threads. r=dougt

xpcom/threads/nsThreadManager.cpp

@@ -160,6 +160,11 @@ nsThreadManager::RegisterCurrentThread(nsThread *thread)
 
   MutexAutoLock lock(*mLock);
 
+  ++mCurrentNumberOfThreads;
+  if (mCurrentNumberOfThreads > mHighestNumberOfThreads) {
+    mHighestNumberOfThreads = mCurrentNumberOfThreads;
+  }
+
   mThreadsByPRThread.Put(thread->GetPRThread(), thread);  // XXX check OOM?
 
   NS_ADDREF(thread);  // for TLS entry
@@ -173,6 +178,7 @@ nsThreadManager::UnregisterCurrentThread(nsThread *thread)
 
   MutexAutoLock lock(*mLock);
 
+  --mCurrentNumberOfThreads;
   mThreadsByPRThread.Remove(thread->GetPRThread());
 
   PR_SetThreadPrivate(mCurThreadIndex, nullptr);
@@ -279,3 +285,10 @@ nsThreadManager::GetIsCycleCollectorThread(bool *result)
   *result = bool(NS_IsCycleCollectorThread());
   return NS_OK;
 }
+
+uint32_t
+nsThreadManager::GetHighestNumberOfThreads()
+{
+  MutexAutoLock lock(*mLock);
+  return mHighestNumberOfThreads;
+}

xpcom/threads/nsThreadManager.h

@@ -42,6 +42,10 @@ public:
   // initialized.
   nsThread *GetCurrentThread();
 
+  // Returns the maximal number of threads that have been in existence
+  // simultaneously during the execution of the thread manager.
+  uint32_t GetHighestNumberOfThreads();
+
   // This needs to be public in order to support static instantiation of this
   // class with older compilers (e.g., egcs-2.91.66).
   ~nsThreadManager() {}
@@ -51,9 +55,11 @@ private:
     : mCurThreadIndex(0)
     , mMainPRThread(nullptr)
     , mLock(nullptr)
-    , mInitialized(false) {
+    , mInitialized(false)
+    , mCurrentNumberOfThreads(1)
+    , mHighestNumberOfThreads(1) {
   }
-  
+
   static nsThreadManager sInstance;
 
   nsRefPtrHashtable<nsPtrHashKey<PRThread>, nsThread> mThreadsByPRThread;
@@ -64,6 +70,11 @@ private:
   // the static context in debug builds.
   nsAutoPtr<mozilla::Mutex> mLock;  // protects tables
   bool                mInitialized;
+
+   // The current number of threads
+   uint32_t           mCurrentNumberOfThreads;
+   // The highest number of threads encountered so far during the session
+   uint32_t           mHighestNumberOfThreads;
 };
 
 #define NS_THREADMANAGER_CID                       \