1/*******************************************************************************
2 * Copyright (C) 2004-2008 Intel Corp. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions are met:
6 *
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8 *    this list of conditions and the following disclaimer.
9 *
10 *  - Redistributions in binary form must reproduce the above copyright notice,
11 *    this list of conditions and the following disclaimer in the documentation
12 *    and/or other materials provided with the distribution.
13 *
14 *  - Neither the name of Intel Corp. nor the names of its
15 *    contributors may be used to endorse or promote products derived from this
16 *    software without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS''
19 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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21 * ARE DISCLAIMED. IN NO EVENT SHALL Intel Corp. OR THE CONTRIBUTORS
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29 *******************************************************************************/
30
31#ifdef HAVE_CONFIG_H
32#include "config.h"
33#endif
34#include "RWLock.h"
35
36RWLock::RWLock() : _counter(0) {}
37
38void 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
63void 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
74void 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