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diff --git a/mojo/system/dispatcher.h b/mojo/system/dispatcher.h
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+// 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 MOJO_SYSTEM_DISPATCHER_H_
+#define MOJO_SYSTEM_DISPATCHER_H_
+
+#include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "base/synchronization/lock.h"
+#include "mojo/public/system/core.h"
+
+namespace mojo {
+namespace system {
+
+class Waiter;
+
+// A |Dispatcher| implements Mojo primitives that are "attached" to a particular
+// handle. This includes most (all?) primitives except for |MojoWait...()|. This
+// object is thread-safe, with its state being protected by a single lock
+// |lock_|, which is also made available to implementation subclasses (via the
+// |lock()| method).
+class Dispatcher : public base::RefCountedThreadSafe<Dispatcher> {
+ public:
+  // These methods implement the various primitives named |Mojo...()|. These
+  // take |lock_| and handle races with |Close()|. Then they call out to
+  // subclasses' |...ImplNoLock()| methods (still under |lock_|), which actually
+  // implement the primitives.
+  // NOTE(vtl): This puts a big lock around each dispatcher (i.e., handle), and
+  // prevents the various |...ImplNoLock()|s from releasing the lock as soon as
+  // possible. If this becomes an issue, we can rethink this.
+  MojoResult Close();
+  MojoResult WriteMessage(const void* bytes,
+                          uint32_t num_bytes,
+                          const MojoHandle* handles,
+                          uint32_t num_handles,
+                          MojoWriteMessageFlags flags);
+  MojoResult ReadMessage(void* bytes,
+                         uint32_t* num_bytes,
+                         MojoHandle* handles,
+                         uint32_t* num_handles,
+                         MojoReadMessageFlags flags);
+
+  // Adds a waiter to this dispatcher. The waiter will be woken up when this
+  // object changes state to satisfy |flags| with result |wake_result| (which
+  // must be >= 0, i.e., a success status). It will also be woken up when it
+  // becomes impossible for the object to ever satisfy |flags| with a suitable
+  // error status.
+  //
+  // Returns:
+  //  - |MOJO_RESULT_OK| if the waiter was added;
+  //  - |MOJO_RESULT_ALREADY_EXISTS| if |flags| is already satisfied;
+  //  - |MOJO_RESULT_INVALID_ARGUMENT| if the dispatcher has been closed; and
+  //  - |MOJO_RESULT_FAILED_PRECONDITION| if it is not (or no longer) possible
+  //    that |flags| will ever be satisfied.
+  MojoResult AddWaiter(Waiter* waiter,
+                       MojoWaitFlags flags,
+                       MojoResult wake_result);
+  void RemoveWaiter(Waiter* waiter);
+
+ protected:
+  Dispatcher();
+
+  friend class base::RefCountedThreadSafe<Dispatcher>;
+  virtual ~Dispatcher();
+
+  // These are to be overridden by subclasses (if necessary). They are called
+  // exactly once -- first |CancelAllWaitersNoLock()|, then |CloseImplNoLock()|,
+  // when the dispatcher is being closed. They are called under |lock_|.
+  virtual void CancelAllWaitersNoLock();
+  virtual MojoResult CloseImplNoLock();
+
+  // These are to be overridden by subclasses (if necessary). They are never
+  // called after the dispatcher has been closed. They are called under |lock_|.
+  virtual MojoResult WriteMessageImplNoLock(const void* bytes,
+                                            uint32_t num_bytes,
+                                            const MojoHandle* handles,
+                                            uint32_t num_handles,
+                                            MojoWriteMessageFlags flags);
+  virtual MojoResult ReadMessageImplNoLock(void* bytes,
+                                           uint32_t* num_bytes,
+                                           MojoHandle* handles,
+                                           uint32_t* num_handles,
+                                           MojoReadMessageFlags flags);
+  virtual MojoResult AddWaiterImplNoLock(Waiter* waiter,
+                                         MojoWaitFlags flags,
+                                         MojoResult wake_result);
+  virtual void RemoveWaiterImplNoLock(Waiter* waiter);
+
+  // Available to subclasses. (Note: Returns a non-const reference, just like
+  // |base::AutoLock|'s constructor takes a non-const reference.
+  base::Lock& lock() const { return lock_; }
+
+ private:
+  // This protects the following members as well as any state added by
+  // subclasses.
+  mutable base::Lock lock_;
+  bool is_closed_;
+
+  DISALLOW_COPY_AND_ASSIGN(Dispatcher);
+};
+
+}  // namespace system
+}  // namespace mojo
+
+#endif  // MOJO_SYSTEM_DISPATCHER_H_