QMutex(3qt)QMutex(3qt)NAME
QMutex - Access serialization between threads
#include <qthread.h>
Inherits Qt.
Public Members
QMutex ( bool recursive = FALSE )
virtual ~QMutex ()
void lock ()
void unlock ()
bool locked ()
DESCRIPTION
The QMutex class provides access serialization between
threads.
The purpose of a QMutex is to protect an object, data
structure or section of code so that only one thread can
access it at a time (In Java terms, this is similar to the
synchronized keyword). For example, say there is a method
which prints a message to the user on two lines:
void someMethod()
{
qDebug("Hello");
qDebug("World");
}
If this method is called simultaneously from two threads
then the following sequence could result:
Hello
Hello
World
World
If we add a mutex:
QMutex mutex;
void someMethod()
{
mutex.lock();
qDebug("Hello");
qDebug("World");
mutex.unlock();
}
In Java terms this would be:
void someMethod()
{
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QMutex(3qt)QMutex(3qt)
synchronized {
qDebug("Hello");
qDebug("World");
}
}
Then only one thread can execute someMethod at a time and
the order of messages is always correct. This is a trivial
example, of course, but applies to any other case where
things need to happen in a particular sequence.
MEMBER FUNCTION DOCUMENTATIONQMutex::QMutex ( bool recursive = FALSE )
Constructs a new mutex. The mutex is created in an
unlocked state. A recursive mutex is created if recursive
is TRUE; a normal mutex is created if recursive is FALSE
(default argument). With a recursive mutex, a thread can
lock the same mutex multiple times and it will not be
unlocked until a corresponding number of unlock() calls
have been made.
QMutex::~QMutex () [virtual]
Destroys the mutex.
void QMutex::lock ()
Attempt to lock the mutex. If another thread has locked
the mutex then this call will block until that thread has
unlocked it.
See also unlock().
bool QMutex::locked ()
Returns TRUE if the mutex is locked by another thread and
FALSE if not.
NOTE: Due to differing implementations of recursive
mutexes on various platforms, calling this function from
the same thread that previous locked the mutex will return
undefined results.
void QMutex::unlock ()
Unlocks the mutex. Attempting to unlock a mutex in a
different thread to the one that locked it results in an
error. Unlocking a mutex that is not locked results in
undefined behaviour (varies between different Operating
Systems' thread implementations).
See also lock().
SEE ALSO
http://doc.trolltech.com/qmutex.html
http://www.trolltech.com/faq/tech.html
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QMutex(3qt)QMutex(3qt)COPYRIGHT
Copyright 1992-2001 Trolltech AS,
http://www.trolltech.com. See the license file included
in the distribution for a complete license statement.
AUTHOR
Generated automatically from the source code.
BUGS
If you find a bug in Qt, please report it as described in
http://doc.trolltech.com/bughowto.html. Good bug reports
make our job much simpler. Thank you.
In case of content or formattting problems with this
manual page, please report them to qt-bugs@trolltech.com.
Please include the name of the manual page (qmutex.3qt)
and the Qt version (2.3.1).
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