1 /* Copyright (c) 2015, The Linux Foundation. All rights reserved.
2 *
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4 * modification, are permitted provided that the following conditions are
5 * met:
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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
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27 *
28 */
29 #ifndef __LOC_SHARED_LOCK__
30 #define __LOC_SHARED_LOCK__
31
32 #include <stddef.h>
33 #ifndef FEATURE_EXTERNAL_AP
34 #include <cutils/atomic.h>
35 #endif /* FEATURE_EXTERNAL_AP */
36 #include <pthread.h>
37
38 #ifdef FEATURE_EXTERNAL_AP
39 #include <atomic>
40
android_atomic_inc(volatile int32_t * addr)41 inline int32_t android_atomic_inc(volatile int32_t *addr)
42 {
43 volatile std::atomic_int_least32_t* a = (volatile std::atomic_int_least32_t*)addr;
44 return std::atomic_fetch_add_explicit(a, 1, std::memory_order_release);
45 }
46
android_atomic_dec(volatile int32_t * addr)47 inline int32_t android_atomic_dec(volatile int32_t *addr)
48 {
49 volatile std::atomic_int_least32_t* a = (volatile std::atomic_int_least32_t*)addr;
50 return std::atomic_fetch_sub_explicit(a, 1, std::memory_order_release);
51 }
52
53 #endif /* FEATURE_EXTERNAL_AP */
54 // This is a utility created for use cases such that there are more than
55 // one client who need to share the same lock, but it is not predictable
56 // which of these clients is to last to go away. This shared lock deletes
57 // itself when the last client calls its drop() method. To add a cient,
58 // this share lock's share() method has to be called, so that the obj
59 // can maintain an accurate client count.
60 class LocSharedLock {
61 volatile int32_t mRef;
62 pthread_mutex_t mMutex;
~LocSharedLock()63 inline ~LocSharedLock() { pthread_mutex_destroy(&mMutex); }
64 public:
65 // first client to create this LockSharedLock
LocSharedLock()66 inline LocSharedLock() : mRef(1) { pthread_mutex_init(&mMutex, NULL); }
67 // following client(s) are to *share()* this lock created by the first client
share()68 inline LocSharedLock* share() { android_atomic_inc(&mRef); return this; }
69 // whe a client no longer needs this shared lock, drop() shall be called.
drop()70 inline void drop() { if (1 == android_atomic_dec(&mRef)) delete this; }
71 // locking the lock to enter critical section
lock()72 inline void lock() { pthread_mutex_lock(&mMutex); }
73 // unlocking the lock to leave the critical section
unlock()74 inline void unlock() { pthread_mutex_unlock(&mMutex); }
75 };
76
77 #endif //__LOC_SHARED_LOCK__
78