60 lines
2.9 KiB
C
60 lines
2.9 KiB
C
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/* 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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