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41 #include "qtlockedfile.h"
46 \brief The QtLockedFile class extends QFile with advisory locking
49 A file may be locked in read or write mode. Multiple instances of
50 \e QtLockedFile, created in multiple processes running on the same
51 machine, may have a file locked in read mode. Exactly one instance
52 may have it locked in write mode. A read and a write lock cannot
53 exist simultaneously on the same file.
55 The file locks are advisory. This means that nothing prevents
56 another process from manipulating a locked file using QFile or
57 file system functions offered by the OS. Serialization is only
58 guaranteed if all processes that access the file use
59 QLockedFile. Also, while holding a lock on a file, a process
60 must not open the same file again (through any API), or locks
61 can be unexpectedly lost.
63 The lock provided by an instance of \e QtLockedFile is released
64 whenever the program terminates. This is true even when the
65 program crashes and no destructors are called.
68 /*! \enum QtLockedFile::LockMode
70 This enum describes the available lock modes.
72 \value ReadLock A read lock.
73 \value WriteLock A write lock.
74 \value NoLock Neither a read lock nor a write lock.
78 Constructs an unlocked \e QtLockedFile object. This constructor
79 behaves in the same way as \e QFile::QFile().
83 QtLockedFile::QtLockedFile()
94 Constructs an unlocked QtLockedFile object with file \a name. This
95 constructor behaves in the same way as \e QFile::QFile(const
100 QtLockedFile::QtLockedFile(const QString &name)
107 m_lock_mode = NoLock;
111 Opens the file in OpenMode \a mode.
113 This is identical to QFile::open(), with the one exception that the
114 Truncate mode flag is disallowed. Truncation would conflict with the
115 advisory file locking, since the file would be modified before the
116 write lock is obtained. If truncation is required, use resize(0)
117 after obtaining the write lock.
119 Returns true if successful; otherwise false.
121 \sa QFile::open(), QFile::resize()
123 bool QtLockedFile::open(OpenMode mode)
125 if (mode & QIODevice::Truncate) {
126 qWarning("QtLockedFile::open(): Truncate mode not allowed.");
129 return QFile::open(mode);
133 Returns \e true if this object has a in read or write lock;
134 otherwise returns \e false.
138 bool QtLockedFile::isLocked() const
140 return m_lock_mode != NoLock;
144 Returns the type of lock currently held by this object, or \e
145 QtLockedFile::NoLock.
149 QtLockedFile::LockMode QtLockedFile::lockMode() const
155 \fn bool QtLockedFile::lock(LockMode mode, bool block = true)
157 Obtains a lock of type \a mode. The file must be opened before it
160 If \a block is true, this function will block until the lock is
161 aquired. If \a block is false, this function returns \e false
162 immediately if the lock cannot be aquired.
164 If this object already has a lock of type \a mode, this function
165 returns \e true immediately. If this object has a lock of a
166 different type than \a mode, the lock is first released and then a
167 new lock is obtained.
169 This function returns \e true if, after it executes, the file is
170 locked by this object, and \e false otherwise.
172 \sa unlock(), isLocked(), lockMode()
176 \fn bool QtLockedFile::unlock()
180 If the object has no lock, this function returns immediately.
182 This function returns \e true if, after it executes, the file is
183 not locked by this object, and \e false otherwise.
185 \sa lock(), isLocked(), lockMode()
189 \fn QtLockedFile::~QtLockedFile()
191 Destroys the \e QtLockedFile object. If any locks were held, they