Allow ObjectWatcher to be used from sequenced tasks.

base/win/object_watcher.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_WIN_OBJECT_WATCHER_H_
 #define BASE_WIN_OBJECT_WATCHER_H_
 
 #include <windows.h>
 
 #include "base/base_export.h"
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
-#include "base/single_thread_task_runner.h"
+#include "base/sequenced_task_runner.h"
 
 namespace base {
 namespace win {
 
 // A class that provides a means to asynchronously wait for a Windows object to
 // become signaled.  It is an abstraction around RegisterWaitForSingleObject
 // that provides a notification callback, OnObjectSignaled, that runs back on
-// the origin thread (i.e., the thread that called StartWatching).
+// the origin sequence (i.e., the sequence that called StartWatching).
 //
 // This class acts like a smart pointer such that when it goes out-of-scope,
 // UnregisterWaitEx is automatically called, and any in-flight notification is
 // suppressed.
 //
 // Typical usage:
 //
 //   class MyClass : public base::win::ObjectWatcher::Delegate {
 //    public:
 //     void DoStuffWhenSignaled(HANDLE object) {
 //       watcher_.StartWatchingOnce(object, this);
 //     }
 //     void OnObjectSignaled(HANDLE object) override {
 //       // OK, time to do stuff!
 //     }
 //    private:
 //     base::win::ObjectWatcher watcher_;
 //   };
 //
 // In the above example, MyClass wants to "do stuff" when object becomes
 // signaled.  ObjectWatcher makes this task easy.  When MyClass goes out of
 // scope, the watcher_ will be destroyed, and there is no need to worry about
 // OnObjectSignaled being called on a deleted MyClass pointer.  Easy!
 // If the object is already signaled before being watched, OnObjectSignaled is
 // still called after (but not necessarily immediately after) watch is started.
 //
 // NOTE: Except for the constructor, all public methods of this class must be
-// called on the same thread. A ThreadTaskRunnerHandle must be set on that
-// thread.
+// called in sequence, in a scope where SequencedTaskRunnerHandle::IsSet().
 class BASE_EXPORT ObjectWatcher {
  public:
   class BASE_EXPORT Delegate {
    public:
     virtual ~Delegate() {}
-    // Called from the thread that started the watch when a signaled object is
+    // Called from the sequence that started the watch when a signaled object is
     // detected. To continue watching the object, StartWatching must be called
     // again.
     virtual void OnObjectSignaled(HANDLE object) = 0;
   };
 
   ObjectWatcher();
   ~ObjectWatcher();
 
-  // When the object is signaled, the given delegate is notified on the thread
+  // When the object is signaled, the given delegate is notified on the sequence
   // where StartWatchingOnce is called. The ObjectWatcher is not responsible for
   // deleting the delegate.
   // Returns whether watching was successfully initiated.
   bool StartWatchingOnce(HANDLE object, Delegate* delegate);
 
-  // Notifies the delegate, on the thread where this method is called, each time
-  // the object is set. By definition, the handle must be an auto-reset object.
-  // The caller must ensure that it (or any Windows system code) doesn't reset
-  // the event or else the delegate won't be called.
+  // Notifies the delegate, on the sequence where this method is called, each
+  // time the object is set. By definition, the handle must be an auto-reset
+  // object. The caller must ensure that it (or any Windows system code) doesn't
+  // reset the event or else the delegate won't be called.
   // Returns whether watching was successfully initiated.
   bool StartWatchingMultipleTimes(HANDLE object, Delegate* delegate);
 
   // Stops watching.  Does nothing if the watch has already completed.  If the
   // watch is still active, then it is canceled, and the associated delegate is
   // not notified.
   //
   // Returns true if the watch was canceled.  Otherwise, false is returned.
   bool StopWatching();
 
@@ skipping 18 matching lines @@
   // A callback pre-bound to Signal() that is posted to the caller's task runner
   // when the wait completes.
   Closure callback_;
 
   // The object being watched.
   HANDLE object_ = nullptr;
 
   // The wait handle returned by RegisterWaitForSingleObject.
   HANDLE wait_object_ = nullptr;
 
-  // The task runner of the thread on which the watch was started.
-  scoped_refptr<SingleThreadTaskRunner> task_runner_;
+  // The task runner of the sequence on which the watch was started.
+  scoped_refptr<SequencedTaskRunner> task_runner_;
 
   bool run_once_ = true;
 
   WeakPtrFactory<ObjectWatcher> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ObjectWatcher);
 };
 
 }  // namespace win
 }  // namespace base
 
 #endif  // BASE_WIN_OBJECT_WATCHER_H_