Detailed Description
The QThread class provides platform-independent threads.
A QThread represents a separate thread of control within the
program; it shares data with all the other threads within the
process but executes independently in the way that a separate
program does on a multitasking operating system. Instead of
starting in main(), QThreads begin executing in run(). You inherit
run() to include your code. For example:
class MyThread : public QThread {
public:
virtual void run();
};
void MyThread::run()
{
for( int count = 0; count < 20; count++ ) {
sleep( 1 );
qDebug( "Ping!" );
}
}
int main()
{
MyThread a;
MyThread b;
a.start();
b.start();
a.wait();
b.wait();
}
This will start two threads, each of which writes Ping! 20 times
to the screen and exits. The wait() calls at the end of main() are
necessary because exiting main() ends the program, unceremoniously
killing all other threads. Each MyThread stops executing when it
reaches the end of MyThread::run(), just as an application does
when it leaves main().
See also Thread Support in Qt, Environment Classes, and Threading.
Member Type Documentation
QThread::Priority
This enum type indicates how the operating system should schedule
newly created threads.
- QThread::IdlePriority - scheduled only when no other threads are
running.
- QThread::LowestPriority - scheduled less often than LowPriority.
- QThread::LowPriority - scheduled less often than NormalPriority.
- QThread::NormalPriority - the default priority of the operating
system.
- QThread::HighPriority - scheduled more often than NormalPriority.
- QThread::HighestPriority - scheduled more often then HighPriority.
- QThread::TimeCriticalPriority - scheduled as often as possible.
- QThread::InheritPriority - use the same priority as the creating
thread. This is the default.
Member Function Documentation
QThread::QThread ( unsigned int stackSize = 0 )
Constructs a new thread. The thread does not begin executing until
start() is called.
If stackSize is greater than zero, the maximum stack size is
set to stackSize bytes, otherwise the maximum stack size is
automatically determined by the operating system.
Warning: Most operating systems place minimum and maximum limits
on thread stack sizes. The thread will fail to start if the stack
size is outside these limits.
QThread::~QThread () [virtual]
QThread destructor.
Note that deleting a QThread object will not stop the execution of
the thread it represents. Deleting a running QThread (i.e.
finished() returns FALSE) will probably result in a program crash.
You can wait() on a thread to make sure that it has finished.
Qt::HANDLE QThread::currentThread () [static]
This returns the thread handle of the currently executing thread.
Warning: The handle returned by this function is used for internal
purposes and should not be used in any application code. On
Windows, the returned value is a pseudo handle for the current
thread, and it cannot be used for numerical comparison.
void QThread::exit () [static]
Ends the execution of the calling thread and wakes up any threads
waiting for its termination.
bool QThread::finished () const
Returns TRUE if the thread is finished; otherwise returns FALSE.
void QThread::msleep ( unsigned long msecs ) [static protected]
System independent sleep. This causes the current thread to sleep
for msecs milliseconds
void QThread::postEvent ( QObject * receiver, QEvent * event ) [static]
This function is obsolete. It is provided to keep old source working. We strongly advise against using it in new code.
Use QApplication::postEvent() instead.
void QThread::run () [pure virtual protected]
This method is pure virtual, and must be implemented in derived
classes in order to do useful work. Returning from this method
will end the execution of the thread.
See also wait().
bool QThread::running () const
Returns TRUE if the thread is running; otherwise returns FALSE.
void QThread::sleep ( unsigned long secs ) [static protected]
System independent sleep. This causes the current thread to sleep
for secs seconds.
void QThread::start ( Priority priority = InheritPriority )
Begins execution of the thread by calling run(), which should be
reimplemented in a QThread subclass to contain your code. The
operating system will schedule the thread according to the priority argument.
If you try to start a thread that is already running, this
function will wait until the the thread has finished and then
restart the thread.
See also Priority.
void QThread::terminate ()
This function terminates the execution of the thread. The thread
may or may not be terminated immediately, depending on the
operating systems scheduling policies. Use QThread::wait()
after terminate() for synchronous termination.
When the thread is terminated, all threads waiting for the
the thread to finish will be woken up.
Warning: This function is dangerous, and its use is discouraged.
The thread can be terminate at any point in its code path. Threads
can be terminated while modifying data. There is no chance for
the thread to cleanup after itself, unlock any held mutexes, etc.
In short, use this function only if absolutely necessary.
void QThread::usleep ( unsigned long usecs ) [static protected]
System independent sleep. This causes the current thread to sleep
for usecs microseconds
bool QThread::wait ( unsigned long time = ULONG_MAX )
A thread calling this function will block until either of these
conditions is met:
- The thread associated with this QThread object has finished
execution (i.e. when it returns from run()). This function
will return TRUE if the thread has finished. It also returns
TRUE if the thread has not been started yet.
- time milliseconds has elapsed. If time is ULONG_MAX (the
default), then the wait will never timeout (the thread must
return from run()). This function will return FALSE if the
wait timed out.
This provides similar functionality to the POSIX pthread_join() function.
This file is part of the Qt toolkit.
Copyright © 1995-2003
Trolltech. All Rights Reserved.
