Bug 1323100 - Add nsThreadManager::NewNamedThread API. r=froydnj

The point of this exercise is to make the thread name available in the thread
func of the thread, so that we can register the thread with the profiler from
the very start of its lifetime, and so that registration and unregistration
can be inside the same function.

MozReview-Commit-ID: DiiMKUQVr55

--HG--
extra : rebase_source : aa1d0c19250765c80c8e8ae59d2752bb4ad7eeac

xpcom/threads/nsIThreadManager.idl

@@ -35,6 +35,20 @@ interface nsIThreadManager : nsISupports
    */
   nsIThread newThread(in unsigned long creationFlags, [optional] in unsigned long stackSize);
 
+  /**
+   * Create a new thread (a global, user PRThread) with the specified name.
+   *
+   * @param name
+   *   The name of the thread. Passing an empty name is equivalent to
+   *   calling newThread(0, stackSize), i.e. the thread will not be named.
+   * @param stackSize
+   *   Number of bytes to reserve for the thread's stack.
+   *
+   * @returns
+   *   The newly created nsIThread object.
+   */
+  [noscript] nsIThread newNamedThread(in ACString name, [optional] in unsigned long stackSize);
+
   /**
    * Get the nsIThread object (if any) corresponding to the given PRThread.
    * This method returns null if there is no corresponding nsIThread.

xpcom/threads/nsThread.cpp

@@ -432,15 +432,30 @@ SetupCurrentThreadForChaosMode()
   }
 }
 
+namespace {
+
+struct ThreadInitData {
+  nsThread* thread;
+  const nsACString& name;
+};
+
+}
+
 /*static*/ void
 nsThread::ThreadFunc(void* aArg)
 {
   using mozilla::ipc::BackgroundChild;
 
-  nsThread* self = static_cast<nsThread*>(aArg);  // strong reference
+  ThreadInitData* initData = static_cast<ThreadInitData*>(aArg);
+  nsThread* self = initData->thread;  // strong reference
+
   self->mThread = PR_GetCurrentThread();
   SetupCurrentThreadForChaosMode();
 
+  if (initData->name.Length() > 0) {
+    PR_SetCurrentThreadName(initData->name.BeginReading());
+  }
+
   // Inform the ThreadManager
   nsThreadManager::get().RegisterCurrentThread(*self);
 
@@ -455,6 +470,9 @@ nsThread::ThreadFunc(void* aArg)
       return;
     }
   }
+
+  initData = nullptr; // clear before unblocking nsThread::Init
+
   event->Run();  // unblocks nsThread::Init
   event = nullptr;
 
@@ -628,7 +646,7 @@ nsThread::~nsThread()
 }
 
 nsresult
-nsThread::Init()
+nsThread::Init(const nsACString& aName)
 {
   // spawn thread and wait until it is fully setup
   RefPtr<nsThreadStartupEvent> startup = new nsThreadStartupEvent();
@@ -639,8 +657,10 @@ nsThread::Init()
 
   mShutdownRequired = true;
 
+  ThreadInitData initData = { this, aName };
+
   // ThreadFunc is responsible for setting mThread
-  if (!PR_CreateThread(PR_USER_THREAD, ThreadFunc, this,
+  if (!PR_CreateThread(PR_USER_THREAD, ThreadFunc, &initData,
                        PR_PRIORITY_NORMAL, PR_GLOBAL_THREAD,
                        PR_JOINABLE_THREAD, mStackSize)) {
     NS_RELEASE_THIS();

xpcom/threads/nsThread.h

@@ -48,8 +48,8 @@ public:
 
   nsThread(MainThreadFlag aMainThread, uint32_t aStackSize);
 
-  // Initialize this as a wrapper for a new PRThread.
-  nsresult Init();
+  // Initialize this as a wrapper for a new PRThread, and optionally give it a name.
+  nsresult Init(const nsACString& aName = NS_LITERAL_CSTRING(""));
 
   // Initialize this as a wrapper for the current PRThread.
   nsresult InitCurrentThread();

xpcom/threads/nsThreadManager.cpp

@@ -248,6 +248,14 @@ NS_IMETHODIMP
 nsThreadManager::NewThread(uint32_t aCreationFlags,
                            uint32_t aStackSize,
                            nsIThread** aResult)
+{
+  return NewNamedThread(NS_LITERAL_CSTRING(""), aStackSize, aResult);
+}
+
+NS_IMETHODIMP
+nsThreadManager::NewNamedThread(const nsACString& aName,
+                                uint32_t aStackSize,
+                                nsIThread** aResult)
 {
   // Note: can be called from arbitrary threads
   
@@ -257,7 +265,7 @@ nsThreadManager::NewThread(uint32_t aCreationFlags,
   }
 
   RefPtr<nsThread> thr = new nsThread(nsThread::NOT_MAIN_THREAD, aStackSize);
-  nsresult rv = thr->Init();  // Note: blocks until the new thread has been set up
+  nsresult rv = thr->Init(aName);  // Note: blocks until the new thread has been set up
   if (NS_FAILED(rv)) {
     return rv;
   }