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2 * Copyright (C) 2004-2008 Intel Corp. All rights reserved.
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5 * modification, are permitted provided that the following conditions are met:
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8 * this list of conditions and the following disclaimer.
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30
31 #ifdef HAVE_CONFIG_H
32 #include "config.h"
33 #endif
34 #include "RWLock.h"
35
RWLock()36 RWLock::RWLock() : _counter(0) {}
37
acquire(const RWMode mode_p)38 void RWLock::acquire(const RWMode mode_p)
39 {
40
41 if (mode_p == READ_ONLY) {
42 //wait for writer's exit
43 _writeSem.acquire();
44 //might be blocked only to decrement _counter and _readSem.release() in release()
45 _countSem.acquire();
46 int tmp = ++_counter;
47 _countSem.release();
48 if (tmp == 1) {
49 //never blocks, no writers, first reader
50 _readSem.acquire();
51 }
52 _writeSem.release();
53 } else {
54 _writeSem.acquire();
55 //wait for reader's exit
56 _readSem.acquire();
57 }
58
59 return;
60 }
61
62 //will do nothing if no read-write lock was acquired
switch2RO()63 void RWLock::switch2RO()
64 {
65 _countSem.acquire();
66 if (!_counter) {
67 _counter = 1;
68 _writeSem.release();
69 }
70 _countSem.release();
71 }
72
73 //will do nothing if no lock was acquired
release()74 void RWLock::release()
75 {
76
77 //might be blocked only to increment _counter in read-only mode
78 _countSem.acquire();
79 if (_counter) {
80 //read-only mode
81 _counter--;
82 if (!_counter) {
83 //the last reader
84 _readSem.release();
85 }
86 } else {
87 //read-write mode
88 _readSem.release();
89 _writeSem.release();
90 }
91 _countSem.release();
92
93 return;
94 }
95
96