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 * 7 * - Redistributions of source code must retain the above copyright notice, 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 20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21 * ARE DISCLAIMED. IN NO EVENT SHALL Intel Corp. OR THE CONTRIBUTORS 22 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28 * POSSIBILITY OF SUCH DAMAGE. 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