/* Copyright (c) 2015, The Linux Foundation. All rights reserved.
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 * modification, are permitted provided that the following conditions are
 * met:
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 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 *       copyright notice, this list of conditions and the following
 *       disclaimer in the documentation and/or other materials provided
 *       with the distribution.
 *     * Neither the name of The Linux Foundation, nor the names of its
 *       contributors may be used to endorse or promote products derived
 *       from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED "AS IS" AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS
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 */
#ifndef __LOC_SHARED_LOCK__
#define __LOC_SHARED_LOCK__

#include <stddef.h>
#include <pthread.h>

// This is a utility created for use cases such that there are more than
// one client who need to share the same lock, but it is not predictable
// which of these clients is to last to go away. This shared lock deletes
// itself when the last client calls its drop() method. To add a cient,
// this share lock's share() method has to be called, so that the obj
// can maintain an accurate client count.
class LocSharedLock {
    uint32_t mRef;
    pthread_mutex_t mMutex;
    inline ~LocSharedLock() { pthread_mutex_destroy(&mMutex); }
public:
    // first client to create this LockSharedLock
    inline LocSharedLock() : mRef(1) { pthread_mutex_init(&mMutex, NULL); }
    // following client(s) are to *share()* this lock created by the first client
    inline LocSharedLock* share() { mRef++; return this; }
    // whe a client no longer needs this shared lock, drop() shall be called.
    inline void drop() { if (0 == --mRef) delete this; }
    // locking the lock to enter critical section
    inline void lock() { pthread_mutex_lock(&mMutex); }
    // unlocking the lock to leave the critical section
    inline void unlock() { pthread_mutex_unlock(&mMutex); }
};

#endif //__LOC_SHARED_LOCK__