Make HostController/DeviceListener deletion fully synchronous.

tools/android/forwarder2/forwarders_manager.h

+// Copyright 2013 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 TOOLS_ANDROID_FORWARDER2_FORWARDERS_MANAGER_H_
+#define TOOLS_ANDROID_FORWARDER2_FORWARDERS_MANAGER_H_
+
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/scoped_vector.h"
+#include "tools/android/forwarder2/pipe_notifier.h"
+
+namespace base {
+
+class SingleThreadTaskRunner;
+
+}  // namespace base
+
+namespace forwarder2 {
+
+class Forwarder;
+class Socket;
+
+// Creates and manages lifetime of a set of Forwarder instances. This class
+// ensures in particular that the forwarder instances are deleted on their
+// construction thread no matter which thread ~ForwardersManager() is called on.
+class ForwardersManager {
+ public:
+  // Can be called on any thread.
+  ForwardersManager();
+  ~ForwardersManager();
+
+  // Note that the (unique) thread that this method is called on must outlive
+  // the ForwardersManager instance. This is needed since the Forwarder
+  // instances are deleted on the thread they were constructed on.
+  void CreateAndStartNewForwarder(scoped_ptr<Socket> socket1,
+                                  scoped_ptr<Socket> socket2);
+
+ private:
+  // Ref-counted thread-safe delegate that can (by definition) outlive its outer
+  // ForwarderManager instance. This is needed since the forwarder instances are
+  // destroyed on a thread other than the one ~ForwardersManager() is called on.
+  // The forwarder instances can also call OnForwarderError() below at any time
+  // on their construction thread (which is the same as their destruction
+  // thread). This means that a WeakPtr to ForwardersManager can't be used
+  // instead of ref-counting since checking the validity of the WeakPtr on a
+  // thread other than the one ~ForwardersManager() is called on would be racy.
+  class Delegate : public base::RefCountedThreadSafe<Delegate> {
+   public:
+    Delegate();
+
+    void Clear();
+
+    void CreateAndStartNewForwarder(scoped_ptr<Socket> socket1,
+                                    scoped_ptr<Socket> socket2);
+
+   private:
+    friend class base::RefCountedThreadSafe<Delegate>;
+
+    virtual ~Delegate();
+
+    void OnForwarderError(scoped_ptr<Forwarder> forwarder);
+
+    void ClearOnForwarderConstructorThread();
+
+    scoped_refptr<base::SingleThreadTaskRunner> forwarders_constructor_runner_;
+    PipeNotifier deletion_notifier_;
+    ScopedVector<Forwarder> forwarders_;
+  };
+
+  const scoped_refptr<Delegate> delegate_;
+};
+
+}  // namespace forwarder2
+
+#endif  // TOOLS_ANDROID_FORWARDER2_FORWARDERS_MANAGER_H_