Fix race between ~SkThreadPool and SkThreadPool::Loop on fDone.

src/utils/SkThreadPool.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkRunnable.h"
 #include "SkThreadPool.h"
 #include "SkThreadUtils.h"
@@ skipping 21 matching lines @@
     if (count < 0) count = num_cores();
     // Create count threads, all running SkThreadPool::Loop.
     for (int i = 0; i < count; i++) {
         SkThread* thread = SkNEW_ARGS(SkThread, (&SkThreadPool::Loop, this));
         *fThreads.append() = thread;
         thread->start();
     }
 }
 
 SkThreadPool::~SkThreadPool() {
+    fReady.lock();
     fDone = true;
-    fReady.lock();
     fReady.broadcast();
     fReady.unlock();
 
     // Wait for all threads to stop.
     for (int i = 0; i < fThreads.count(); i++) {
         fThreads[i]->join();
         SkDELETE(fThreads[i]);
     }
 }
 
@@ skipping 44 matching lines @@
     }
 
     // We have some threads.  Queue it up!
     fReady.lock();
     LinkedRunnable* linkedRunnable = SkNEW(LinkedRunnable);
     linkedRunnable->fRunnable = r;
     fQueue.addToHead(linkedRunnable);
     fReady.signal();
     fReady.unlock();
 }