I know that I can run a background process in python using subprocess. But the problem is that when I make a gui and then use subprocess with close_fds=True parameter, the window changes to not responding.
So, what I want is that I need to create a background process but it should run separately along with the main process and when that process is done, it should again combine with the main process.
BTW, I am using PySide2 as the gui framework
Any help would be appreciated
I think what would be more beneficial to you would be threading, you are able to start a process in another thread without blocking the main thread which runs your gui. Once the other thread has completed its task it will join the main thread
Related
From my wxpython GUI app I have an rsync task that I kick off as a multiprocessing.Process.
The idea is to update a wx.textCtrl with the constant output from this background process.
I am using a pubsub subscribe method.
The functions work fine but I can't get the textCtrl to update.
If I use a CallAfter method I get this crash/error:
The process has forked and you cannot use this CoreFoundation
functionality safely. You MUST exec(). Break on
THE_PROCESS_HAS_FORKED_AND_YOU_CANNOT_USE_THIS_COREFOUNDATION_FUNCTIONALITY___YOU_MUST_EXEC()
to debug.
If I don't use that method and I try to append the text directly to the textctrl nothing happens.
Any ideas?
Thanks!
Adam
The problem is that the child process can't write back to the main process. Use a queue to pass messages back to the main process, and update the control from within a timer or a background thread that waits for messages from the queue.
I am a bit confused with multiprocessing. I have a video processing script which can be run from the command line or launched from a PySide application using a subprocess call. The script seems to run fine from the command line and basically initializes a pool of workers which each process a separate video file.
When I run the program however the OS tells me my program is not responding. I would like to make use of all the cores on my system for multiprocessing but I would also like to prevent this annoyance. What should I do I get around this? Do I start the initial script in a thread or something?
As you are speaking of PySide, I assume you program is a GUI one. In a GUI program all processing must occurs in a worker thread if you want to keep the UI responsive. So yes, the initial script must be start in a thread distinct from main thread (main one is reserved for UI)
I created a GUI with PyQt which implements the buttons "Start" and "Stop".
When I click on "Start" a huge python Script is started. The function of "Stop" has to end this python script, but when I start the script it runs and I can't stop it. I even can't activate anything else on the GUI and I get no reaction from it. So i have to wait the long time until the python script ends.
How can I implement the methods so that I can interrupt the script with the "Stop" button even when I want?
Since you do everything in the QButton.clicked signal, your GUI locks up until you exit that function.
My solution i used in a small project was to seperate it into a GUI and worker process.
Use multiprocessing.Process to do your processing and have it send the results over a multiprocessing.Pipe.
The worker also has a second Pipe to recieve commands (my project just uses one command - exit)
In the GUI, you create 2 Pipes: one for results, one for commands.
Initialize the worker with both pipes and start the process.
The next step would be to have a QTimer poll the pipe for results and display them.
By doing so, your UI stays responsive while the calculations happen in the background.
I have a PyQt4 application, which at some point packs a big file using the tarfile module. Since the tarfile module does not implement any callback strategy, it blocks and the Qt GUI gets unresponsive.
I want the GUI to keep updating during that time. The only possibility is a separate thread.
So, I start a QThread. What do I have to do in the QThread to make the GUI update itself?
As soon, as the tar process is finished, I want the thread to finish.
Thanks!
Nathan
QThread's are pretty much identical to normal Python threads so you can just use normal communication methods. However, QThreads also have a few signals available, so if you simply connect to those, than you're done.
In your GUI code do something like this and you're pretty much done:
thread = Thread()
thread.finished.connect(gui.do_update_thingy)
There is also a terminated and started signal available which you can use :)
Python have been really bumpy for me, because the last time I created a GUI client, the client seems to hang when spawning a process, calling a shell script, and calling outside application.
This have been my major problem with Python since then, and now I'm in a new project, can someone give me pointers, and a word of advice in order for my GUI python application to still be interactive when spawning another process?
Simplest (not necessarily "best" in an abstract sense): spawn the subprocess in a separate thread, communicating results back to the main thread via a Queue.Queue instance -- the main thread must periodically check that queue to see if the results have arrived yet, but periodic polling isn't hard to arrange in any event loop.
Your main GUI thread will freeze if you spawn off a process and wait for it to completely. Often, you can simply use subprocess and poll it now and then for completion rather than waiting for it to finish. This will keep your GUI from freezing.