[PyQt] graphical file tail

Eric Frederich eric.frederich at gmail.com
Tue Jun 25 01:49:06 BST 2013

Thanks for the suggestions.  Unfortunately I do need to use Qt 4.6.2 from
RHEL 6.  This will also be on an NFS mounted drive.

This is for a GUI that monitors the output of jobs run on Sun Grid Engine
(SGE).  So its not that the files _happen_ to be on NFS, it's actually
_required_ that they are :-(

Any Qt4 help would be appreciated.
Am I cleaning up my tail processes correctly?  Is it just the QThreads I'm
screwing up?  Are there other hidden dangers with my implementation?
On Jun 24, 2013 7:25 PM, "John Lee" <jjl at pobox.com> wrote:

> On Mon, 24 Jun 2013, Eric Frederich wrote:
>  I'm trying to tail several files graphically.
>> I have been trying to find a way to tail several files in a GUI
>> without much luck at all.
>> I get errors from tail saying broken pipe.
>> I get PyQt errors saying underlying C++ objects have been destroyed.
>> I get other Qt errors saying that threads are still running when the
>> application exits
>> etc....
>> The implementation posted below seems to suffer from the following errors.
>> Not all the time.  It depends.
>> QThread: Destroyed while thread is still running
>> QWaitCondition::wakeAll(): mutex lock failure:
> You're not calling .wait on the threads, and you probably want to give
> e.g. your QObjects a parent where you can, so that Qt manages the lifetime
> of the wrapped C++ objects (e.g. pass in self to the parent arg of the
> QTextBrowser constructor).
> But, I recommend doing it a different way: I find event-based code easier
> to think about than threads.  So, if you can use Qt5, you might want to do
> away with the threads and the tail subprocess and replace them with
> QFileSystemWatcher.  Use event-based code instead of the threads (I'm not
> talking about Qt events, I just mean hook up to the signals that that class
> emits and process a little input at a time so as to avoid blocking the UI,
> using QTimer where needed).  I say Qt5 because Qt4 isn't very friendly to
> this way of working since it uses threads in the implementation of
> QFileSystemWatcher.
> Caveat: QFileSystemWatcher still has its problems, but the ones discussed
> at the URL below are more convenience issues than fundamental problems: I
> just found I had to experiment a bit to see when the different signals got
> emitted.
> http://blog.rburchell.com/**2012/03/qt-51-aka-when-**
> qfilesystemwatcher-might.html<http://blog.rburchell.com/2012/03/qt-51-aka-when-qfilesystemwatcher-might.html>
> Caveat #2: I imagine QFileSystemWatcher does not support filesystems like
> NFS, at least on Linux kernels with inotify support (but don't take my word
> for it, check the source).
> John
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