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      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_EDK_SYSTEM_WAITER_H_
      6 #define MOJO_EDK_SYSTEM_WAITER_H_
      7 
      8 #include <stdint.h>
      9 
     10 #include "base/logging.h"
     11 #include "base/macros.h"
     12 #include "base/synchronization/condition_variable.h"
     13 #include "base/synchronization/lock.h"
     14 #include "mojo/edk/system/awakable.h"
     15 #include "mojo/edk/system/system_impl_export.h"
     16 #include "mojo/public/c/system/types.h"
     17 
     18 namespace mojo {
     19 namespace edk {
     20 
     21 // IMPORTANT (all-caps gets your attention, right?): |Waiter| methods are called
     22 // under other locks, in particular, |Dispatcher::lock_|s, so |Waiter| methods
     23 // must never call out to other objects (in particular, |Dispatcher|s). This
     24 // class is thread-safe.
     25 class MOJO_SYSTEM_IMPL_EXPORT Waiter final : public Awakable {
     26  public:
     27   Waiter();
     28   ~Waiter();
     29 
     30   // A |Waiter| can be used multiple times; |Init()| should be called before
     31   // each time it's used.
     32   void Init();
     33 
     34   // Waits until a suitable |Awake()| is called. (|context| may be null, in
     35   // which case, obviously no context is ever returned.)
     36   // Returns:
     37   //   - The result given to the first call to |Awake()| (possibly before this
     38   //     call to |Wait()|); in this case, |*context| is set to the value passed
     39   //     to that call to |Awake()|.
     40   //   - |MOJO_RESULT_DEADLINE_EXCEEDED| if the deadline was exceeded; in this
     41   //     case |*context| is not modified.
     42   //
     43   // Usually, the context passed to |Awake()| will be the value passed to
     44   // |Dispatcher::AddAwakable()|, which is usually the index to the array of
     45   // handles passed to |MojoWaitMany()| (or 0 for |MojoWait()|).
     46   //
     47   // Typical |Awake()| results are:
     48   //   - |MOJO_RESULT_OK| if one of the flags passed to
     49   //     |MojoWait()|/|MojoWaitMany()| (hence |Dispatcher::AddAwakable()|) was
     50   //     satisfied;
     51   //   - |MOJO_RESULT_CANCELLED| if a handle (on which
     52   //     |MojoWait()|/|MojoWaitMany()| was called) was closed (hence the
     53   //     dispatcher closed); and
     54   //   - |MOJO_RESULT_FAILED_PRECONDITION| if one of the set of flags passed to
     55   //     |MojoWait()|/|MojoWaitMany()| cannot or can no longer be satisfied by
     56   //     the corresponding handle (e.g., if the other end of a message or data
     57   //     pipe is closed).
     58   MojoResult Wait(MojoDeadline deadline, uintptr_t* context);
     59 
     60   // Wake the waiter up with the given result and context (or no-op if it's been
     61   // woken up already).
     62   bool Awake(MojoResult result, uintptr_t context) override;
     63 
     64  private:
     65   base::Lock lock_;             // Protects the following members.
     66   base::ConditionVariable cv_;  // Associated to |lock_|.
     67 #if DCHECK_IS_ON()
     68   bool initialized_;
     69 #endif
     70   bool awoken_;
     71   MojoResult awake_result_;
     72   uintptr_t awake_context_;
     73 
     74   DISALLOW_COPY_AND_ASSIGN(Waiter);
     75 };
     76 
     77 }  // namespace edk
     78 }  // namespace mojo
     79 
     80 #endif  // MOJO_EDK_SYSTEM_WAITER_H_
     81