gps/utils/LocSharedLock.h

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#ifndef __LOC_SHARED_LOCK__
#define __LOC_SHARED_LOCK__

#include <stddef.h>
#ifndef FEATURE_EXTERNAL_AP
#include <cutils/atomic.h>
#endif /* FEATURE_EXTERNAL_AP */
#include <pthread.h>

#ifdef FEATURE_EXTERNAL_AP
#include <atomic>

inline int32_t android_atomic_inc(volatile int32_t *addr)
{
    volatile std::atomic_int_least32_t* a = (volatile std::atomic_int_least32_t*)addr;
    return std::atomic_fetch_add_explicit(a, 1, std::memory_order_release);
}

inline int32_t android_atomic_dec(volatile int32_t *addr)
{
    volatile std::atomic_int_least32_t* a = (volatile std::atomic_int_least32_t*)addr;
    return std::atomic_fetch_sub_explicit(a, 1, std::memory_order_release);
}
#endif /* FEATURE_EXTERNAL_AP */

namespace loc_util {

// 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 {
    volatile int32_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() { android_atomic_inc(&mRef); return this; }
    // whe a client no longer needs this shared lock, drop() shall be called.
    inline void drop() { if (1 == android_atomic_dec(&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); }
};

} //namespace loc_util

#endif //__LOC_SHARED_LOCK__