Clean VM thread shutdown:

runtime/vm/thread_pool.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_THREAD_POOL_H_
 #define VM_THREAD_POOL_H_
 
+#include "vm/allocation.h"
 #include "vm/globals.h"
 #include "vm/os_thread.h"
 
 namespace dart {
 
 class ThreadPool {
  public:
   // Subclasses of Task are able to run on a ThreadPool.
   class Task {
    protected:
     Task();
 
    public:
     virtual ~Task();
 
     // Override this to provide task-specific behavior.
     virtual void Run() = 0;
 
    private:
     DISALLOW_COPY_AND_ASSIGN(Task);
   };
 
   ThreadPool();
 
-  // Shuts down this thread pool.  Causes workers to terminate
+  // Shuts down this thread pool. Causes workers to terminate
   // themselves when they are active again.
   ~ThreadPool();
 
   // Runs a task on the thread pool.
   void Run(Task* task);
 
   // Some simple stats.
   uint64_t workers_running() const { return count_running_; }
   uint64_t workers_idle() const { return count_idle_; }
   uint64_t workers_started() const { return count_started_; }
   uint64_t workers_stopped() const { return count_stopped_; }
 
  private:
-  friend class ThreadPoolTestPeer;
-
   class Worker {
    public:
     explicit Worker(ThreadPool* pool);
 
     // Sets a task on the worker.
     void SetTask(Task* task);
 
     // Starts the thread for the worker.  This should only be called
     // after a task has been set by the initial call to SetTask().
     void StartThread();
 
-    // Main loop for a worker.
-    void Loop();
+    // Main loop for a worker. Returns true if worker is removed from thread
+    // lists, false otherwise.
+    bool Loop();
 
     // Causes worker to terminate eventually.
     void Shutdown();
 
+    // Get the Worker's thread id.
+    ThreadId id() { return id_; }
+
    private:
     friend class ThreadPool;
 
     // The main entry point for new worker threads.
     static void Main(uword args);
 
-    bool IsDone() const { return pool_ == NULL; }
+    bool IsDone() const { return done_; }
 
     // Fields owned by Worker.
     Monitor monitor_;
     ThreadPool* pool_;
+    bool done_;
     Task* task_;
+    ThreadId id_;
+    bool started_;
 
     // Fields owned by ThreadPool.  Workers should not look at these
     // directly.  It's like looking at the sun.
     bool owned_;         // Protected by ThreadPool::mutex_
     Worker* all_next_;   // Protected by ThreadPool::mutex_
     Worker* idle_next_;  // Protected by ThreadPool::mutex_
 
+    Worker* shutdown_next_;  // Protected by ThreadPool::exit_monitor
+
     DISALLOW_COPY_AND_ASSIGN(Worker);
   };
 
   void Shutdown();
 
   // Expensive.  Use only in assertions.
   bool IsIdle(Worker* worker);
 
   bool RemoveWorkerFromIdleList(Worker* worker);
   bool RemoveWorkerFromAllList(Worker* worker);
 
+  void AddWorkerToShutdownList(Worker* worker);
+  bool RemoveWorkerFromShutdownList(Worker* worker);
+
   // Worker operations.
   void SetIdle(Worker* worker);
   bool ReleaseIdleWorker(Worker* worker);
 
   Mutex mutex_;
   bool shutting_down_;
   Worker* all_workers_;
   Worker* idle_workers_;
   uint64_t count_started_;
   uint64_t count_stopped_;
   uint64_t count_running_;
   uint64_t count_idle_;
 
-  static Monitor* exit_monitor_;  // Used only in testing.
-  static int* exit_count_;        // Used only in testing.
+  Monitor exit_monitor_;
+  Worker* shutting_down_workers_;
 
   DISALLOW_COPY_AND_ASSIGN(ThreadPool);
 };
 
 }  // namespace dart
 
 #endif  // VM_THREAD_POOL_H_