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 <stdint.h> 9 10 #include "base/macros.h" 11 #include "base/synchronization/condition_variable.h" 12 #include "base/synchronization/lock.h" 13 #include "mojo/public/c/system/types.h" 14 #include "mojo/system/system_impl_export.h" 15 16 namespace mojo { 17 namespace system { 18 19 // IMPORTANT (all-caps gets your attention, right?): |Waiter| methods are called 20 // under other locks, in particular, |Dispatcher::lock_|s, so |Waiter| methods 21 // must never call out to other objects (in particular, |Dispatcher|s). This 22 // class is thread-safe. 23 class MOJO_SYSTEM_IMPL_EXPORT Waiter { 24 public: 25 Waiter(); 26 ~Waiter(); 27 28 // A |Waiter| can be used multiple times; |Init()| should be called before 29 // each time it's used. 30 void Init(); 31 32 // Waits until a suitable |Awake()| is called. (|context| may be null, in 33 // which case, obviously no context is ever returned.) 34 // Returns: 35 // - The result given to the first call to |Awake()| (possibly before this 36 // call to |Wait()|); in this case, |*context| is set to the value passed 37 // to that call to |Awake()|. 38 // - |MOJO_RESULT_DEADLINE_EXCEEDED| if the deadline was exceeded; in this 39 // case |*context| is not modified. 40 // 41 // Usually, the context passed to |Awake()| will be the value passed to 42 // |Dispatcher::AddWaiter()|, which is usually the index to the array of 43 // handles passed to |MojoWaitMany()| (or 0 for |MojoWait()|). 44 // 45 // Typical |Awake()| results are: 46 // - |MOJO_RESULT_OK| if one of the flags passed to 47 // |MojoWait()|/|MojoWaitMany()| (hence |Dispatcher::AddWaiter()|) was 48 // satisfied; 49 // - |MOJO_RESULT_CANCELLED| if a handle (on which 50 // |MojoWait()|/|MojoWaitMany()| was called) was closed (hence the 51 // dispatcher closed); and 52 // - |MOJO_RESULT_FAILED_PRECONDITION| if one of the set of flags passed to 53 // |MojoWait()|/|MojoWaitMany()| cannot or can no longer be satisfied by 54 // the corresponding handle (e.g., if the other end of a message or data 55 // pipe is closed). 56 MojoResult Wait(MojoDeadline deadline, uint32_t* context); 57 58 // Wake the waiter up with the given result and context (or no-op if it's been 59 // woken up already). 60 void Awake(MojoResult result, uint32_t context); 61 62 private: 63 base::ConditionVariable cv_; // Associated to |lock_|. 64 base::Lock lock_; // Protects the following members. 65 #ifndef NDEBUG 66 bool initialized_; 67 #endif 68 bool awoken_; 69 MojoResult awake_result_; 70 // This is a |uint32_t| because we really only need to store an index (for 71 // |MojoWaitMany()|). But in tests, it's convenient to use this for other 72 // purposes (e.g., to distinguish between different wake-up reasons). 73 uint32_t awake_context_; 74 75 DISALLOW_COPY_AND_ASSIGN(Waiter); 76 }; 77 78 } // namespace system 79 } // namespace mojo 80 81 #endif // MOJO_SYSTEM_WAITER_H_ 82