qmutex.3qt

Trolltech公司发布的基于C++图形开发环境

'\" t
.TH QMutex 3qt "24 January 2005" "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
.br
.PP
\fC#include <qthread.h>\fR
.PP
Inherits Qt.
.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
.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");
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     qDebug("World");
.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
.fi
.PP
If we add a mutex:
.PP
.nf
.br
  QMutex mutex;
.br
.br
  void someMethod()
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  {
.br
     mutex.lock();
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     qDebug("Hello");
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     qDebug("World");
.br
     mutex.unlock();
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  }
.fi
.PP
In Java terms this would be:
.PP
.nf
.br
  void someMethod()
.br
  {
.br
     synchronized {
.br
       qDebug("Hello");
.br
       qDebug("World");
.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.
.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 (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.
.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 block until that thread has unlocked it.
.PP
See also unlock().
.SH "bool QMutex::locked ()"
Returns TRUE if the mutex is locked by another thread and FALSE if not.
.PP
\fINOTE:\fR 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.
.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().
.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 make our job much simpler. Thank you.
.P
In case of content or formattting problems with this manual page, please
report them to
.BR [e-mail] .
Please include the name of the manual page (qmutex.3qt) and the Qt
version (2.3.10).