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