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.
42class LocSharedLock {
43    volatile int32_t mRef;
44    pthread_mutex_t mMutex;
45    inline ~LocSharedLock() { pthread_mutex_destroy(&mMutex); }
46public:
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