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Qt-interest Archive, February 2008
QSocketNotifier fires non stop

Message 1 in thread

Hi all,
i'm trying to use a QSocketNotifier to watch a file for data to be read.
But my connected slot is called over and over again even though there are no 
bytes available and i'm reading away all the data anyway.

QFile( path );
file.open( QIODevice::ReadOnly );
QSocketNotifier *notifier = new QSocketNotifier( file.handle(), 
QSocketNotifier::Read, this );
connect(m_notifier, SIGNAL(activated(int)), this, SLOT(slotReadyRead(int)));

void slotReadyRead(int) {
  file.readAll();
 ...
}

This is basicaly what i do. Documentation of QSocketNotifier gives no hints 
on the problem.
I'm developing a non-gui application under linux.


Any ideas?






....Volker

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Message 2 in thread

On Monday 04 February 2008 11:27:54 Volker wrote:
> Hi all,
> i'm trying to use a QSocketNotifier to watch a file for data to be read.
> But my connected slot is called over and over again even though there are
> no bytes available and i'm reading away all the data anyway.
>
> QFile( path );
> file.open( QIODevice::ReadOnly );
> QSocketNotifier *notifier = new QSocketNotifier( file.handle(),
> QSocketNotifier::Read, this );
> connect(m_notifier, SIGNAL(activated(int)), this,
> SLOT(slotReadyRead(int)));
>
> void slotReadyRead(int) {
>   file.readAll();
>  ...
> }
>
> This is basicaly what i do. Documentation of QSocketNotifier gives no hints
> on the problem.
> I'm developing a non-gui application under linux.
>
>
> Any ideas?

QSocketNotifier's behaviour on files and other random-access devices is not 
documented. It's entirely unsupported.

You shouldn't be using it for anything other than a socket. Using it on pipes 
or character-special devices may work, but is also unsupported.

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Message 3 in thread

Thiago Macieira 04.02.2008 14:40:
> On Monday 04 February 2008 11:27:54 Volker wrote:
> > Hi all,
> > i'm trying to use a QSocketNotifier to watch a file for data to be read.
> > But my connected slot is called over and over again even though there are
> > no bytes available and i'm reading away all the data anyway.
> >
> > QFile( path );
> > file.open( QIODevice::ReadOnly );
> > QSocketNotifier *notifier = new QSocketNotifier( file.handle(),
> > QSocketNotifier::Read, this );
> > connect(m_notifier, SIGNAL(activated(int)), this,
> > SLOT(slotReadyRead(int)));
> >
> > void slotReadyRead(int) {
> >   file.readAll();
> >  ...
> > }
> >
> > This is basicaly what i do. Documentation of QSocketNotifier gives no
> > hints on the problem.
> > I'm developing a non-gui application under linux.
> >
> >
> > Any ideas?
>
> QSocketNotifier's behaviour on files and other random-access devices is not
> documented. It's entirely unsupported.
>
> You shouldn't be using it for anything other than a socket. Using it on
> pipes or character-special devices may work, but is also unsupported.

I see. Maybe this remark should go in the docs of QSocketNotifier.

Is there a recommended  method for watching a file? 
In my case its a logfile which is written by another process.

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Message 4 in thread

On Monday 04 February 2008 15:07:05 Volker wrote:
> I see. Maybe this remark should go in the docs of QSocketNotifier.

Isn't the fact that it is called *socket* notifier enough? Anything else is 
platform-specific behaviour. And undocumented stuff is not supported.

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Message 5 in thread

Volker wrote:
> Is there a recommended method for watching a file?
> In my case its a logfile which is written by another process.
Will the QFileSystemWatcher do what you want?
    http://doc.trolltech.com/qfilesystemwatcher.html

D

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