source: smplayer/trunk/src/qtsingleapplication/qtlockedfile.cpp@ 130

Last change on this file since 130 was 128, checked in by Silvan Scherrer, 14 years ago

SMPlayer: trunk update to latest svn
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1/****************************************************************************
2**
3** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
4** All rights reserved.
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6** Contact: Nokia Corporation (qt-info@nokia.com)
7**
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13** modification, are permitted provided that the following conditions are
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22** the names of its contributors may be used to endorse or promote
23** products derived from this software without specific prior written
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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*/
82QtLockedFile::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*/
99QtLockedFile::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*/
122bool 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*/
137bool 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*/
148QtLockedFile::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*/
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