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      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