1 /*
2  * Copyright (C) 2015 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 
18 #ifndef ANDROID_SERVICE_UTILS_SCOPED_CONDITION_H
19 #define ANDROID_SERVICE_UTILS_SCOPED_CONDITION_H
20 
21 #include <utils/Timers.h>
22 #include <utils/Condition.h>
23 #include <utils/Errors.h>
24 #include <utils/Mutex.h>
25 
26 #include <memory>
27 
28 namespace android {
29 
30 /**
31  * WaitableMutexWrapper can be used with AutoConditionLock to construct scoped locks for the
32  * wrapped Mutex with timeouts for lock acquisition.
33  */
34 class WaitableMutexWrapper {
35     friend class AutoConditionLock;
36 public:
37     /**
38      * Construct the ConditionManger with the given Mutex.
39      */
40     explicit WaitableMutexWrapper(Mutex* mutex);
41 
42     virtual ~WaitableMutexWrapper();
43 private:
44     Mutex* mMutex;
45     bool mState;
46     Condition mCondition;
47 };
48 
49 /**
50  * AutoConditionLock is a scoped lock similar to Mutex::Autolock, but allows timeouts to be
51  * specified for lock acquisition.
52  *
53  * AutoConditionLock is used with a WaitableMutexWrapper to lock/unlock the WaitableMutexWrapper's
54  * wrapped Mutex, and wait/set/signal the WaitableMutexWrapper's wrapped condition. To use this,
55  * call AutoConditionLock::waitAndAcquire to get an instance.  This will:
56  *      - Lock the given WaitableMutexWrapper's mutex.
57  *      - Wait for the WaitableMutexWrapper's condition to become false, or timeout.
58  *      - Set the WaitableMutexWrapper's condition to true.
59  *
60  * When the AutoConditionLock goes out of scope and is destroyed, this will:
61  *      - Set the WaitableMutexWrapper's condition to false.
62  *      - Signal threads waiting on this condition to wakeup.
63  *      - Release WaitableMutexWrapper's mutex.
64  */
65 class AutoConditionLock final {
66 public:
67     AutoConditionLock() = delete;
68     AutoConditionLock(const AutoConditionLock& other) = delete;
69     AutoConditionLock & operator=(const AutoConditionLock&) = delete;
70 
71     ~AutoConditionLock();
72 
73     /**
74      * Make a new AutoConditionLock from a given WaitableMutexWrapper, waiting up to waitTime
75      * nanoseconds to acquire the WaitableMutexWrapper's wrapped lock.
76      *
77      * Return an empty unique_ptr if this fails, or a timeout occurs.
78      */
79     static std::unique_ptr<AutoConditionLock> waitAndAcquire(
80             const std::shared_ptr<WaitableMutexWrapper>& manager, nsecs_t waitTime);
81 
82     /**
83      * Make a new AutoConditionLock from a given WaitableMutexWrapper, waiting indefinitely to
84      * acquire the WaitableMutexWrapper's wrapped lock.
85      *
86      * Return an empty unique_ptr if this fails.
87      */
88     static std::unique_ptr<AutoConditionLock> waitAndAcquire(
89             const std::shared_ptr<WaitableMutexWrapper>& manager);
90 private:
91     explicit AutoConditionLock(const std::shared_ptr<WaitableMutexWrapper>& manager);
92 
93     std::shared_ptr<WaitableMutexWrapper> mManager;
94     Mutex::Autolock mAutoLock;
95     bool mAcquired;
96 };
97 
98 }; // namespace android
99 
100 #endif // ANDROID_SERVICE_UTILS_SCOPED_CONDITION_H
101