[Interest] Fwd: how to run 21 threads concurrently

[Sascha Cunz]

Am Freitag, 5. Oktober 2012, 20:20:40 schrieb Sujan Dasmahapatra:
> This code snippet is nomore hanging. i did some mistake. but it's still the
> same. not writing some data to the file. problem persists. whats still
> going wrong please help.
> 
> [code]
> 
> 
> QSemaphore mSemaphore1;
> 
> int nZ=1;
> 
> for (int z=0;z<nZ;z++)
> 
> {
> 
> Q_ASSERT( &mSemaphore1 );
> 
> Th = QtConcurrent::run(
> 
> this,&UNRSTParser::ProcessZLayer,z);
> 


> mSemaphore1.release(1);

This release is at the wrong place. It belong to the _end_ of 
UNRSTParser::ProcessZLayer. That's why I put a helper-class into my example.

Doing it here renders the Semaphore useless - Because you want the below 
acquire() to _block until all QFutures are finished_.

> values += (nX*nY);
> 
> }
> 
> mSemaphore1.acquire(nZ);
> 
> 
> [/code]
> 
> On Fri, Oct 5, 2012 at 2:12 PM, Jan Kundrát <jkt at flaska.net> wrote:
> > On 10/05/12 00:27, Sascha Cunz wrote:
> > > But, after all, the above code is a so called busy-loop. It will eat up
> > 
> > 1 core
> > 
> > > almost completely (At least on most OS-configurations).
> > 
> > Are you sure that a call to QFuture::waitForFinished() consumes CPU?
> > That would be highly suspicious. Yes, the call will block and wait until
> > the QFuture succeeds, but that's different from what a busy loop is.
> > 
> > Using waitForFinished() on each future is easier and more
> > straightforward than adding semaphores.
> > 
> > With kind regards,
> > Jan
> > 
> > --
> > Trojita, a fast e-mail client -- http://trojita.flaska.net/
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