Initial in-process implementation of some Mojo primitives.

mojo/system/waiter.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 MOJO_SYSTEM_WAITER_H_
+#define MOJO_SYSTEM_WAITER_H_
+
+#include "base/basictypes.h"
+#include "base/synchronization/condition_variable.h"
+#include "base/synchronization/lock.h"
+#include "mojo/public/system/core.h"
+
+namespace mojo {
+namespace system {
+
+// IMPORTANT (all-caps gets your attention, right?): |Waiter| methods are called
+// under other locks, in particular, |Dispatcher::lock_|s, so |Waiter| methods
+// must never call out to other objects (in particular, |Dispatcher|s). This
+// class is thread-safe.
+class Waiter {
+ public:
+  Waiter();
+  ~Waiter();
+
+  // A |Waiter| can be used multiple times; |Init()| should be called before
+  // each time it's used.
+  void Init();
+
+  // Waits until a suitable |Awake()| is called.
+  // Returns:
+  //  - The |wake_result| passed to |Dispatcher::AddWaiter()| if it was woken up
+  //    by that dispatcher for the reason specified by |flags| (in the call to
+  //    |AddWaiter()|).
+  //  - |MOJO_RESULT_CANCELLED| if a handle (on which |MojoWait()| was called)
+  //    was closed; and
+  //  - |MOJO_RESULT_FAILED_PRECONDITION| if the reasons for being awoken given
+  //    by |flags| cannot (or can no longer) be satisfied (e.g., if the other
+  //    end of a pipe is closed).
+  MojoResult Wait(MojoDeadline deadline);
+
+  // Wake the waiter up with the given result (or no-op if it's been woken up
+  // already).
+  void Awake(MojoResult wait_result);
+
+ private:
+  base::ConditionVariable cv_;  // Associated to |lock_|.
+  base::Lock lock_;  // Protects the following members.
+  bool awoken_;
+  MojoResult wait_result_;
+
+  DISALLOW_COPY_AND_ASSIGN(Waiter);
+};
+
+}  // namespace system
+}  // namespace mojo
+
+#endif  // MOJO_SYSTEM_WAITER_H_