1 /* Copyright (c) 2015, The Linux Foundation. All rights reserved. 2 * 3 * Redistribution and use in source and binary forms, with or without 4 * modification, are permitted provided that the following conditions are 5 * met: 6 * * Redistributions of source code must retain the above copyright 7 * notice, this list of conditions and the following disclaimer. 8 * * Redistributions in binary form must reproduce the above 9 * copyright notice, this list of conditions and the following 10 * disclaimer in the documentation and/or other materials provided 11 * with the distribution. 12 * * Neither the name of The Linux Foundation, nor the names of its 13 * contributors may be used to endorse or promote products derived 14 * from this software without specific prior written permission. 15 * 16 * THIS SOFTWARE IS PROVIDED "AS IS" AND ANY EXPRESS OR IMPLIED 17 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 18 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT 19 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS 20 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 21 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 22 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR 23 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 24 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE 25 * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN 26 * IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 * 28 */ 29 #ifndef __LOC_SHARED_LOCK__ 30 #define __LOC_SHARED_LOCK__ 31 32 #include <stddef.h> 33 #include <cutils/atomic.h> 34 #include <pthread.h> 35 36 // This is a utility created for use cases such that there are more than 37 // one client who need to share the same lock, but it is not predictable 38 // which of these clients is to last to go away. This shared lock deletes 39 // itself when the last client calls its drop() method. To add a cient, 40 // this share lock's share() method has to be called, so that the obj 41 // can maintain an accurate client count. 42 class LocSharedLock { 43 volatile int32_t mRef; 44 pthread_mutex_t mMutex; 45 inline ~LocSharedLock() { pthread_mutex_destroy(&mMutex); } 46 public: 47 // first client to create this LockSharedLock 48 inline LocSharedLock() : mRef(1) { pthread_mutex_init(&mMutex, NULL); } 49 // following client(s) are to *share()* this lock created by the first client 50 inline LocSharedLock* share() { android_atomic_inc(&mRef); return this; } 51 // whe a client no longer needs this shared lock, drop() shall be called. 52 inline void drop() { if (1 == android_atomic_dec(&mRef)) delete this; } 53 // locking the lock to enter critical section 54 inline void lock() { pthread_mutex_lock(&mMutex); } 55 // unlocking the lock to leave the critical section 56 inline void unlock() { pthread_mutex_unlock(&mMutex); } 57 }; 58 59 #endif //__LOC_SHARED_LOCK__ 60
