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59 lines
2.9 KiB
59 lines
2.9 KiB
/* Copyright (c) 2015, The Linux Foundation. All rights reserved. |
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* |
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* Redistribution and use in source and binary forms, with or without |
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* modification, are permitted provided that the following conditions are |
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* met: |
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* * Redistributions of source code must retain the above copyright |
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* notice, this list of conditions and the following disclaimer. |
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* * Redistributions in binary form must reproduce the above |
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* copyright notice, this list of conditions and the following |
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* disclaimer in the documentation and/or other materials provided |
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* with the distribution. |
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* * Neither the name of The Linux Foundation, nor the names of its |
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* contributors may be used to endorse or promote products derived |
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* from this software without specific prior written permission. |
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* |
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* THIS SOFTWARE IS PROVIDED "AS IS" AND ANY EXPRESS OR IMPLIED |
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* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF |
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT |
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS |
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR |
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* BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, |
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* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE |
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* OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN |
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* IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
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* |
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*/ |
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#ifndef __LOC_SHARED_LOCK__ |
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#define __LOC_SHARED_LOCK__ |
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#include <stddef.h> |
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#include <cutils/atomic.h> |
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#include <pthread.h> |
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// This is a utility created for use cases such that there are more than |
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// one client who need to share the same lock, but it is not predictable |
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// which of these clients is to last to go away. This shared lock deletes |
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// itself when the last client calls its drop() method. To add a cient, |
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// this share lock's share() method has to be called, so that the obj |
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// can maintain an accurate client count. |
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class LocSharedLock { |
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volatile int32_t mRef; |
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pthread_mutex_t mMutex; |
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inline ~LocSharedLock() { pthread_mutex_destroy(&mMutex); } |
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public: |
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// first client to create this LockSharedLock |
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inline LocSharedLock() : mRef(1) { pthread_mutex_init(&mMutex, NULL); } |
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// following client(s) are to *share()* this lock created by the first client |
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inline LocSharedLock* share() { android_atomic_inc(&mRef); return this; } |
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// whe a client no longer needs this shared lock, drop() shall be called. |
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inline void drop() { if (1 == android_atomic_dec(&mRef)) delete this; } |
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// locking the lock to enter critical section |
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inline void lock() { pthread_mutex_lock(&mMutex); } |
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// unlocking the lock to leave the critical section |
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inline void unlock() { pthread_mutex_unlock(&mMutex); } |
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}; |
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#endif //__LOC_SHARED_LOCK__
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