1 /* Copyright (c) 2015, The Linux Foundation. All rights reserved.
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28  */
29 #ifndef __LOC_SHARED_LOCK__
30 #define __LOC_SHARED_LOCK__
31 
32 #include <stddef.h>
33 #include <pthread.h>
34 
35 // This is a utility created for use cases such that there are more than
36 // one client who need to share the same lock, but it is not predictable
37 // which of these clients is to last to go away. This shared lock deletes
38 // itself when the last client calls its drop() method. To add a cient,
39 // this share lock's share() method has to be called, so that the obj
40 // can maintain an accurate client count.
41 class LocSharedLock {
42     uint32_t mRef;
43     pthread_mutex_t mMutex;
~LocSharedLock()44     inline ~LocSharedLock() { pthread_mutex_destroy(&mMutex); }
45 public:
46     // first client to create this LockSharedLock
LocSharedLock()47     inline LocSharedLock() : mRef(1) { pthread_mutex_init(&mMutex, NULL); }
48     // following client(s) are to *share()* this lock created by the first client
share()49     inline LocSharedLock* share() { mRef++; return this; }
50     // whe a client no longer needs this shared lock, drop() shall be called.
drop()51     inline void drop() { if (0 == --mRef) delete this; }
52     // locking the lock to enter critical section
lock()53     inline void lock() { pthread_mutex_lock(&mMutex); }
54     // unlocking the lock to leave the critical section
unlock()55     inline void unlock() { pthread_mutex_unlock(&mMutex); }
56 };
57 
58 #endif //__LOC_SHARED_LOCK__
59