| /* |
| * Copyright 2016, The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| #ifndef STAGEFRIGHT_FOUNDATION_MUTEXED_H_ |
| #define STAGEFRIGHT_FOUNDATION_MUTEXED_H_ |
| |
| #include <utils/Mutex.h> |
| #include <utils/Condition.h> |
| |
| namespace android { |
| |
| /* |
| * Wrapper class to programmatically protect a structure using a mutex. |
| * |
| * Mutexed<> objects contain a built-in mutex. Protection is enforced because the structure can |
| * only be accessed by locking the mutex first. |
| * |
| * Usage: |
| * |
| * struct DataToProtect { |
| * State(int var1) : mVar1(var1), mVar2(0) { } |
| * int mVar1; |
| * int mVar2; |
| * Condition mCondition1; |
| * }; |
| * |
| * Mutexed<DataToProtect> mProtectedData; |
| * |
| * // members are inaccessible via mProtectedData directly |
| * |
| * void someFunction() { |
| * Mutexed<DataToProtect>::Locked data(mProtectedData); // access the protected data |
| * |
| * // the mutex is locked here, so accessing the data is safe |
| * |
| * if (data->mVar1 < 5) { |
| * ++data->mVar2; |
| * } |
| * |
| * // if you need to temporarily unlock the mutex, you can use unlock/relock mutex locally |
| * // using the accessor object. |
| * |
| * data.unlock(); |
| * |
| * // data is inaccessible here |
| * |
| * doSomeLongOperation(); |
| * |
| * data.lock(); |
| * |
| * // data is now accessible again. Note: it may have changed since unlock(). |
| * |
| * // you can use the integral mutex to wait for a condition |
| * |
| * data.waitForCondition(data->mCondition1); |
| * |
| * helper(&data); |
| * } |
| * |
| * void trigger() { |
| * Mutexed<DataToProtect>::Locked data(mProtectedData); |
| * data->mCondition1.signal(); |
| * } |
| * |
| * void helper(const Mutexed<DataToProtect>::Locked &data) { |
| * data->mVar1 = 3; |
| * } |
| * |
| */ |
| |
| template<typename T> |
| class Mutexed { |
| public: |
| /* |
| * Accessor-guard of the mutex-protected structure. This can be dereferenced to |
| * access the structure (using -> or * operators). |
| * |
| * Upon creation, the mutex is locked. You can use lock()/unlock() methods to |
| * temporarily lock/unlock the mutex. Using any references to the underlying |
| * structure or its members defeats the protection of this class, so don't do |
| * it. |
| * |
| * Note: The accessor-guard itself is not thread-safe. E.g. you should not call |
| * unlock() or lock() from different threads; they must be called from the thread |
| * that locked the original wrapper. |
| * |
| * Also note: Recursive locking/unlocking is not supported by the accessor. This |
| * is as intended, as it allows lenient locking/unlocking via multiple code paths. |
| */ |
| class Locked { |
| public: |
| inline Locked(Mutexed<T> &mParent); |
| inline Locked(Locked &&from) : |
| mLock(from.mLock), |
| mTreasure(from.mTreasure), |
| mLocked(from.mLocked) {} |
| inline ~Locked(); |
| |
| // dereference the protected structure. This returns nullptr if the |
| // mutex is not locked by this accessor-guard. |
| inline T* operator->() const { return mLocked ? &mTreasure : nullptr; } |
| inline T& operator*() const { return mLocked ? mTreasure : *(T*)nullptr; } |
| |
| // same as * |
| inline T& get() const { return mLocked ? mTreasure : *(T*)nullptr; } |
| // sets structure. this will abort if mLocked is false. |
| inline void set(T& o) const { get() = o; } |
| |
| // Wait on the condition variable using lock. Must be locked. |
| inline status_t waitForCondition(Condition &cond) { return cond.wait(mLock); } |
| |
| // same with relative timeout |
| inline status_t waitForConditionRelative(Condition &cond, nsecs_t reltime) { |
| return cond.waitRelative(mLock, reltime); |
| } |
| |
| // unlocks the integral mutex. No-op if the mutex was already unlocked. |
| inline void unlock(); |
| |
| // locks the integral mutex. No-op if the mutex was already locked. |
| inline void lock(); |
| |
| private: |
| Mutex &mLock; |
| T &mTreasure; |
| bool mLocked; |
| |
| // disable copy constructors |
| Locked(const Locked&) = delete; |
| void operator=(const Locked&) = delete; |
| }; |
| |
| // Wrap all constructors of the underlying structure |
| template<typename ...Args> |
| Mutexed(Args... args) : mTreasure(args...) { } |
| |
| ~Mutexed() { } |
| |
| // Lock the mutex, and create an accessor-guard (a Locked object) to access the underlying |
| // structure. This returns an object that dereferences to the wrapped structure when the mutex |
| // is locked by it, or otherwise to "null". |
| // This is just a shorthand for Locked() constructor to avoid specifying the template type. |
| inline Locked lock() { |
| return Locked(*this); |
| } |
| |
| private: |
| friend class Locked; |
| Mutex mLock; |
| T mTreasure; |
| |
| // disable copy constructors |
| Mutexed(const Mutexed<T>&) = delete; |
| void operator=(const Mutexed<T>&) = delete; |
| }; |
| |
| template<typename T> |
| inline Mutexed<T>::Locked::Locked(Mutexed<T> &mParent) |
| : mLock(mParent.mLock), |
| mTreasure(mParent.mTreasure), |
| mLocked(true) { |
| mLock.lock(); |
| } |
| |
| template<typename T> |
| inline Mutexed<T>::Locked::~Locked() { |
| if (mLocked) { |
| mLock.unlock(); |
| } |
| } |
| |
| template<typename T> |
| inline void Mutexed<T>::Locked::unlock() { |
| if (mLocked) { |
| mLocked = false; |
| mLock.unlock(); |
| } |
| } |
| |
| template<typename T> |
| inline void Mutexed<T>::Locked::lock() { |
| if (!mLocked) { |
| mLock.lock(); |
| mLocked = true; |
| } |
| } |
| |
| } // namespace android |
| |
| #endif |