qmutex.3qt

linux下GUI编程工具qt的在线连接帮助手册

'\" t
.TH QMutex 3qt "11 October 2001" "Trolltech AS" \" -*- nroff -*-
.\" Copyright 1992-2001 Trolltech AS.  All rights reserved.  See the
.\" license file included in the distribution for a complete license
.\" statement.
.\"
.ad l
.nh
.SH NAME
QMutex \- Access serialization between threads
.PP
\fC#include <qmutex.h>\fR
.PP
.SS "Public Members"
.in +1c
.ti -1c
.BI "\fBQMutex\fR ( bool recursive = FALSE )"
.br
.ti -1c
.BI "virtual \fB~QMutex\fR ()"
.br
.ti -1c
.BI "void \fBlock\fR ()"
.br
.ti -1c
.BI "void \fBunlock\fR ()"
.br
.ti -1c
.BI "bool \fBlocked\fR ()"
.br
.ti -1c
.BI "bool \fBtryLock\fR ()"
.br
.in -1c
.SH DESCRIPTION
The QMutex class provides access serialization between threads.
.PP
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:
.PP
.nf
.br
  void someMethod()
.br
  {
.br
     qDebug("Hello");
.br
     qDebug("World");
.br
  }
.br
.fi
.PP
If this method is called simultaneously from two threads then the following sequence could result:
.PP
.nf
.br
  Hello
.br
  Hello
.br
  World
.br
  World
.br
.fi
.PP
If we add a mutex:
.PP
.nf
.br
  QMutex mutex;
.br
.br
  void someMethod()
.br
  {
.br
     mutex.lock();
.br
     qDebug("Hello");
.br
     qDebug("World");
.br
     mutex.unlock();
.br
  }
.br
.fi
.PP
In Java terms this would be:
.PP
.nf
.br
  void someMethod()
.br
  {
.br
     synchronized {
.br
       qDebug("Hello");
.br
       qDebug("World");
.br
     }
.br
  }
.br
.fi
.PP
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.
.PP
When you call lock() in a thread, other threads that try to call lock() in the same place will block until the thread that got the lock calls unlock(). A non-blocking alternative to lock() is tryLock().
.PP
See also Environment Classes and Threading.
.SH MEMBER FUNCTION DOCUMENTATION
.SH "QMutex::QMutex ( bool recursive = FALSE )"
Constructs a new mutex. The mutex is created in an unlocked state. A recursive mutex is created if \fIrecursive\fR is TRUE; a normal mutex is created if \fIrecursive\fR is FALSE (the default). 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.
.SH "QMutex::~QMutex ()\fC [virtual]\fR"
Destroys the mutex.
.SH "void QMutex::lock ()"
Attempt to lock the mutex. If another thread has locked the mutex then this call will \fIblock\fR until that thread has unlocked it.
.PP
See also unlock() and locked().
.SH "bool QMutex::locked ()"
Returns TRUE if the mutex is locked by another thread; otherwise returns FALSE.
.PP
\fBWarning:\fR Due to differing implementations of recursive mutexes on various platforms, calling this function from the same thread that previously locked the mutex will return undefined results.
.PP
See also lock() and unlock().
.SH "bool QMutex::tryLock ()"
Attempt to lock the mutex. If the lock was obtained, this function returns TRUE. If another thread has locked the mutex, this function returns FALSE, instead of waiting for the mutex to become available, i.e. it does not block.
.PP
The mutex must be unlocked with unlock() before another thread can successfully lock it.
.PP
See also lock(), unlock() and locked().
.SH "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).
.PP
See also lock() and locked().

.SH "SEE ALSO"
.BR http://doc.trolltech.com/qmutex.html
.BR http://www.trolltech.com/faq/tech.html
.SH COPYRIGHT
Copyright 1992-2001 Trolltech AS, http://www.trolltech.com.  See the
license file included in the distribution for a complete license
statement.
.SH AUTHOR
Generated automatically from the source code.
.SH BUGS
If you find a bug in Qt, please report it as described in
.BR http://doc.trolltech.com/bughowto.html .
Good bug reports help us to help you. Thank you.
.P
The definitive Qt documentation is provided in HTML format; it is
located at $QTDIR/doc/html and can be read using Qt Assistant or with
a web browser. This man page is provided as a convenience for those
users who prefer man pages, although this format is not officially
supported by Trolltech. 
.P
If you find errors in this manual page, please report them to
.BR [e-mail] .
Please include the name of the manual page (qmutex.3qt) and the Qt
version (3.0.0).