Re: [PyQt] graphical file tail
On Mon Jun 24 20:24:25 BST 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. [...] Basically, I want to graphically tail files and when the GUI closes the tail subprocesses are killed. Seems like a simple request, but I can't get it right. I notice that other messages have been talking about solving problems in your original implementation, but how about trying a different approach? The simple example below uses QProcess to show the output from a command. In this case, tail -f file. It will stop the process when the window is closed, but not the process creating the file, of course. David #!/usr/bin/env python import sys from PyQt4.QtCore import * from PyQt4.QtGui import * class TailWidget(QTextBrowser): def __init__(self, parent = None): QTextBrowser.__init__(self, parent) self.process = QProcess() self.process.readyReadStandardOutput.connect(self.addStdout) self.process.readyReadStandardError.connect(self.addStderr) self.process.finished.connect(self.stop) self.running = False def start(self, command, arguments): if self.running: return self.running = True self.process.start(command, arguments) def stop(self): self.running = False def addStdout(self): self.append(QString.fromLocal8Bit(self.process.readAllStandardOutput())) def addStderr(self): self.append(QString.fromLocal8Bit(self.process.readAllStandardError())) def closeEvent(self, event): if self.running: self.process.terminate() self.process.waitForFinished(1000) event.accept() if __name__ == __main__: app = QApplication(sys.argv) if len(app.arguments()) != 2: sys.stderr.write(Usage: %s file\n % app.arguments()[0]) sys.exit(1) w = TailWidget() w.start(tail, [-f, app.arguments()[1]]) w.show() sys.exit(app.exec_()) ___ PyQt mailing listPyQt@riverbankcomputing.com http://www.riverbankcomputing.com/mailman/listinfo/pyqt
Re: [PyQt] graphical file tail
Thanks David, This example works nicely. It's nice to find out what you did wrong, but I'm always open to new implementations. In fact that is what I wanted, was someone to do it their way so I could compare. I'm sure I was doing something terribly wrong but didn't want to post a do it for me email so I provided the implementation that I tried ;-) Thanks, ~Eric On Tue, Jun 25, 2013 at 8:22 AM, David Boddie david.bod...@met.no wrote: On Mon Jun 24 20:24:25 BST 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. [...] Basically, I want to graphically tail files and when the GUI closes the tail subprocesses are killed. Seems like a simple request, but I can't get it right. I notice that other messages have been talking about solving problems in your original implementation, but how about trying a different approach? The simple example below uses QProcess to show the output from a command. In this case, tail -f file. It will stop the process when the window is closed, but not the process creating the file, of course. David #!/usr/bin/env python import sys from PyQt4.QtCore import * from PyQt4.QtGui import * class TailWidget(QTextBrowser): def __init__(self, parent = None): QTextBrowser.__init__(self, parent) self.process = QProcess() self.process.readyReadStandardOutput.connect(self.addStdout) self.process.readyReadStandardError.connect(self.addStderr) self.process.finished.connect(self.stop) self.running = False def start(self, command, arguments): if self.running: return self.running = True self.process.start(command, arguments) def stop(self): self.running = False def addStdout(self): self.append(QString.fromLocal8Bit(self.process.readAllStandardOutput())) def addStderr(self): self.append(QString.fromLocal8Bit(self.process.readAllStandardError())) def closeEvent(self, event): if self.running: self.process.terminate() self.process.waitForFinished(1000) event.accept() if __name__ == __main__: app = QApplication(sys.argv) if len(app.arguments()) != 2: sys.stderr.write(Usage: %s file\n % app.arguments()[0]) sys.exit(1) w = TailWidget() w.start(tail, [-f, app.arguments()[1]]) w.show() sys.exit(app.exec_()) ___ PyQt mailing listPyQt@riverbankcomputing.com http://www.riverbankcomputing.com/mailman/listinfo/pyqt ___ PyQt mailing listPyQt@riverbankcomputing.com http://www.riverbankcomputing.com/mailman/listinfo/pyqt
Re: [PyQt] graphical file tail
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 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 ___ PyQt mailing listPyQt@riverbankcomputing.com http://www.riverbankcomputing.com/mailman/listinfo/pyqt
Re: [PyQt] graphical file tail
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 j...@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.htmlhttp://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 __**_ PyQt mailing listPyQt@riverbankcomputing.com http://www.riverbankcomputing.**com/mailman/listinfo/pyqthttp://www.riverbankcomputing.com/mailman/listinfo/pyqt ___ PyQt mailing listPyQt@riverbankcomputing.com http://www.riverbankcomputing.com/mailman/listinfo/pyqt
