1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
|
/* Copyright (c) 2015, The Linux Foundation. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
* * Redistributions of source code must retain the above copyright
* 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
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
* BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
* OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
* IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
*/
#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 */
// 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); }
};
#endif //__LOC_SHARED_LOCK__
|
