mojo/system/waiter.h

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef MOJO_SYSTEM_WAITER_H_
   6 #define MOJO_SYSTEM_WAITER_H_
   7
   8 #include "base/basictypes.h"
   9 #include "base/synchronization/condition_variable.h"
  10 #include "base/synchronization/lock.h"
  11 #include "mojo/public/c/system/types.h"
  12 #include "mojo/system/system_impl_export.h"
  13
  14 namespace mojo {
  15 namespace system {
  16
  17 // IMPORTANT (all-caps gets your attention, right?): |Waiter| methods are called
  18 // under other locks, in particular, |Dispatcher::lock_|s, so |Waiter| methods
  19 // must never call out to other objects (in particular, |Dispatcher|s). This
  20 // class is thread-safe.
  21 class MOJO_SYSTEM_IMPL_EXPORT Waiter {
  22  public:
  23   Waiter();
  24   ~Waiter();
  25
  26   // A |Waiter| can be used multiple times; |Init()| should be called before
  27   // each time it's used.
  28   void Init();
  29
  30   // Waits until a suitable |Awake()| is called.
  31   // Returns:
  32   //  - The |wake_result| passed to |Dispatcher::AddWaiter()| if it was woken up
  33   //    by that dispatcher for the reason specified by |flags| (in the call to
  34   //    |AddWaiter()|).
  35   //  - |MOJO_RESULT_CANCELLED| if a handle (on which |MojoWait()| was called)
  36   //    was closed; and
  37   //  - |MOJO_RESULT_FAILED_PRECONDITION| if the reasons for being awoken given
  38   //    by |flags| cannot (or can no longer) be satisfied (e.g., if the other
  39   //    end of a pipe is closed).
  40   MojoResult Wait(MojoDeadline deadline);
  41
  42   // Wake the waiter up with the given result (or no-op if it's been woken up
  43   // already).
  44   void Awake(MojoResult wait_result);
  45
  46  private:
  47   base::ConditionVariable cv_;  // Associated to |lock_|.
  48   base::Lock lock_;  // Protects the following members.
  49 #ifndef NDEBUG
  50   bool initialized_;
  51 #endif
  52   bool awoken_;
  53   MojoResult wait_result_;
  54
  55   DISALLOW_COPY_AND_ASSIGN(Waiter);
  56 };
  57
  58 }  // namespace system
  59 }  // namespace mojo
  60
  61 #endif  // MOJO_SYSTEM_WAITER_H_