| 1 | /**************************************************************************** |
| 2 | ** |
| 3 | ** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies). |
| 4 | ** All rights reserved. |
| 5 | ** |
| 6 | ** Contact: Nokia Corporation (qt-info@nokia.com) |
| 7 | ** |
| 8 | ** This file is part of a Qt Solutions component. |
| 9 | ** |
| 10 | ** You may use this file under the terms of the BSD license as follows: |
| 11 | ** |
| 12 | ** "Redistribution and use in source and binary forms, with or without |
| 13 | ** modification, are permitted provided that the following conditions are |
| 14 | ** met: |
| 15 | ** * Redistributions of source code must retain the above copyright |
| 16 | ** notice, this list of conditions and the following disclaimer. |
| 17 | ** * Redistributions in binary form must reproduce the above copyright |
| 18 | ** notice, this list of conditions and the following disclaimer in |
| 19 | ** the documentation and/or other materials provided with the |
| 20 | ** distribution. |
| 21 | ** * Neither the name of Nokia Corporation and its Subsidiary(-ies) nor |
| 22 | ** the names of its contributors may be used to endorse or promote |
| 23 | ** products derived from this software without specific prior written |
| 24 | ** permission. |
| 25 | ** |
| 26 | ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| 27 | ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| 28 | ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| 29 | ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| 30 | ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| 31 | ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| 32 | ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| 33 | ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| 34 | ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| 35 | ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| 36 | ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE." |
| 37 | ** |
| 38 | ****************************************************************************/ |
| 39 | |
| 40 | #include "qtlockedfile.h" |
| 41 | |
| 42 | /*! |
| 43 | \class QtLockedFile |
| 44 | |
| 45 | \brief The QtLockedFile class extends QFile with advisory locking |
| 46 | functions. |
| 47 | |
| 48 | A file may be locked in read or write mode. Multiple instances of |
| 49 | \e QtLockedFile, created in multiple processes running on the same |
| 50 | machine, may have a file locked in read mode. Exactly one instance |
| 51 | may have it locked in write mode. A read and a write lock cannot |
| 52 | exist simultaneously on the same file. |
| 53 | |
| 54 | The file locks are advisory. This means that nothing prevents |
| 55 | another process from manipulating a locked file using QFile or |
| 56 | file system functions offered by the OS. Serialization is only |
| 57 | guaranteed if all processes that access the file use |
| 58 | QLockedFile. Also, while holding a lock on a file, a process |
| 59 | must not open the same file again (through any API), or locks |
| 60 | can be unexpectedly lost. |
| 61 | |
| 62 | The lock provided by an instance of \e QtLockedFile is released |
| 63 | whenever the program terminates. This is true even when the |
| 64 | program crashes and no destructors are called. |
| 65 | */ |
| 66 | |
| 67 | /*! \enum QtLockedFile::LockMode |
| 68 | |
| 69 | This enum describes the available lock modes. |
| 70 | |
| 71 | \value ReadLock A read lock. |
| 72 | \value WriteLock A write lock. |
| 73 | \value NoLock Neither a read lock nor a write lock. |
| 74 | */ |
| 75 | |
| 76 | /*! |
| 77 | Constructs an unlocked \e QtLockedFile object. This constructor |
| 78 | behaves in the same way as \e QFile::QFile(). |
| 79 | |
| 80 | \sa QFile::QFile() |
| 81 | */ |
| 82 | QtLockedFile::QtLockedFile() |
| 83 | : QFile() |
| 84 | { |
| 85 | #ifdef Q_OS_WIN |
| 86 | wmutex = 0; |
| 87 | rmutex = 0; |
| 88 | #endif |
| 89 | m_lock_mode = NoLock; |
| 90 | } |
| 91 | |
| 92 | /*! |
| 93 | Constructs an unlocked QtLockedFile object with file \a name. This |
| 94 | constructor behaves in the same way as \e QFile::QFile(const |
| 95 | QString&). |
| 96 | |
| 97 | \sa QFile::QFile() |
| 98 | */ |
| 99 | QtLockedFile::QtLockedFile(const QString &name) |
| 100 | : QFile(name) |
| 101 | { |
| 102 | #ifdef Q_OS_WIN |
| 103 | wmutex = 0; |
| 104 | rmutex = 0; |
| 105 | #endif |
| 106 | m_lock_mode = NoLock; |
| 107 | } |
| 108 | |
| 109 | /*! |
| 110 | Opens the file in OpenMode \a mode. |
| 111 | |
| 112 | This is identical to QFile::open(), with the one exception that the |
| 113 | Truncate mode flag is disallowed. Truncation would conflict with the |
| 114 | advisory file locking, since the file would be modified before the |
| 115 | write lock is obtained. If truncation is required, use resize(0) |
| 116 | after obtaining the write lock. |
| 117 | |
| 118 | Returns true if successful; otherwise false. |
| 119 | |
| 120 | \sa QFile::open(), QFile::resize() |
| 121 | */ |
| 122 | bool QtLockedFile::open(OpenMode mode) |
| 123 | { |
| 124 | if (mode & QIODevice::Truncate) { |
| 125 | qWarning("QtLockedFile::open(): Truncate mode not allowed."); |
| 126 | return false; |
| 127 | } |
| 128 | return QFile::open(mode); |
| 129 | } |
| 130 | |
| 131 | /*! |
| 132 | Returns \e true if this object has a in read or write lock; |
| 133 | otherwise returns \e false. |
| 134 | |
| 135 | \sa lockMode() |
| 136 | */ |
| 137 | bool QtLockedFile::isLocked() const |
| 138 | { |
| 139 | return m_lock_mode != NoLock; |
| 140 | } |
| 141 | |
| 142 | /*! |
| 143 | Returns the type of lock currently held by this object, or \e |
| 144 | QtLockedFile::NoLock. |
| 145 | |
| 146 | \sa isLocked() |
| 147 | */ |
| 148 | QtLockedFile::LockMode QtLockedFile::lockMode() const |
| 149 | { |
| 150 | return m_lock_mode; |
| 151 | } |
| 152 | |
| 153 | /*! |
| 154 | \fn bool QtLockedFile::lock(LockMode mode, bool block = true) |
| 155 | |
| 156 | Obtains a lock of type \a mode. The file must be opened before it |
| 157 | can be locked. |
| 158 | |
| 159 | If \a block is true, this function will block until the lock is |
| 160 | aquired. If \a block is false, this function returns \e false |
| 161 | immediately if the lock cannot be aquired. |
| 162 | |
| 163 | If this object already has a lock of type \a mode, this function |
| 164 | returns \e true immediately. If this object has a lock of a |
| 165 | different type than \a mode, the lock is first released and then a |
| 166 | new lock is obtained. |
| 167 | |
| 168 | This function returns \e true if, after it executes, the file is |
| 169 | locked by this object, and \e false otherwise. |
| 170 | |
| 171 | \sa unlock(), isLocked(), lockMode() |
| 172 | */ |
| 173 | |
| 174 | /*! |
| 175 | \fn bool QtLockedFile::unlock() |
| 176 | |
| 177 | Releases a lock. |
| 178 | |
| 179 | If the object has no lock, this function returns immediately. |
| 180 | |
| 181 | This function returns \e true if, after it executes, the file is |
| 182 | not locked by this object, and \e false otherwise. |
| 183 | |
| 184 | \sa lock(), isLocked(), lockMode() |
| 185 | */ |
| 186 | |
| 187 | /*! |
| 188 | \fn QtLockedFile::~QtLockedFile() |
| 189 | |
| 190 | Destroys the \e QtLockedFile object. If any locks were held, they |
| 191 | are released. |
| 192 | */ |