How to modify a textview from a different process ?

Question

So I am making a GUI to get tweets. I have made an event box which would take the signal and change the textview. I am using multiprocessing to change the textview, but it just doesn't change. I even tried changing the size of the window. But nothing changes. I can get textbuffer of the textview but can not change it.

import pygtk
pygtk.require('2.0')
import gtk
from multiprocessing import Process

class multi:
    def __init__(self):
        self.window = gtk.Window(gtk.WINDOW_TOPLEVEL)
        self.window.set_size_request(800,400)
        self.window.set_title("Twitter Box")
        self.window.set_border_width(4)
        self.window.connect("destroy", self.close_application)

        self.vbox1 = gtk.EventBox()
        self.vbox1.set_size_request(750,450)
        self.vbox1.connect('leave_notify_event',self.go_multi)
        self.window.add(self.vbox1)
        self.vbox1.show()

        self.tweetview = gtk.TextView()
        self.tweetbuffer = self.tweetview.get_buffer()
        self.tweetbuffer.set_text('Why not working?')
        self.vbox1.add(self.tweetview)
        self.tweetview.show()

        self.window.show()

    def close_application(self, widget):
        gtk.main_quit()

    def go_multi(self, widget, data=None):
        p = Process(target = self.change_textview)
        p.start()
        p.join()

    def change_textview(self):
        print 'changing text'
        startiter = self.tweetbuffer.get_start_iter()
        enditer = self.tweetbuffer.get_end_iter()
        text = self.tweetbuffer.get_text(startiter, enditer)
        print text
        if text:
            self.tweetbuffer.set_text('Changed....')
        else:
            self.tweetbuffer.set_text('')
        return 

def main():
    multi()
    gtk.main()

if __name__ == '__main__':
    main()

I am making GUI to get tweets. Sometimes it takes really long to retrieve timeline due to slow connectivity and the GUI freezes. So, I wanted to make it such that, it would create a process and it will fetch the timeline and set tweetbuffer. But I am unable to set text in tweetbuffer.

Answer 1

If you still want to continue on that way after all answers:
Disclaimer:
I have no idea how useful this answer.
Explanation:
I tried to use your logic. I also imported Queue to share some data between processes. I guess it was needed as I saw from documentation. You may find some other info in code sample below.

import pygtk
pygtk.require('2.0')
import gtk
from multiprocessing import Process, Queue

class multi:
    def __init__(self):
        self.window = gtk.Window(gtk.WINDOW_TOPLEVEL)
        self.window.set_size_request(800,400)
        self.window.set_title("Twitter Box")
        self.window.set_border_width(4)
        self.window.connect("destroy", self.close_application)

        self.vbox1 = gtk.EventBox()
        self.vbox1.set_size_request(750,450)
        self.vbox1.connect('leave_notify_event',self.go_multi)
        self.window.add(self.vbox1)
        self.vbox1.show()
        self.tweetview = gtk.TextView()
        self.tweetbuffer = self.tweetview.get_buffer()
        self.tweetbuffer.set_text('Why not working?')
        self.vbox1.add(self.tweetview)
        self.tweetview.show()

        self.window.show()

    def close_application(self, widget):
        gtk.main_quit()

    def go_multi(self, widget, data=None):
        q = Queue()
        p = Process(target = self.change_textview, args=(q,))
        p.start()
        self.tweetbuffer.set_text(q.get())
        p.join()

    def change_textview(self, q):
        print 'changing text'
        startiter = self.tweetbuffer.get_start_iter()
        enditer = self.tweetbuffer.get_end_iter()
        text = self.tweetbuffer.get_text(startiter, enditer)
        print text
        if text:
            q.put(('Changed....'))
        else:
            q.put((''))
def main():
    multi()
    gtk.main()

if __name__ == '__main__':
    main()

Answer 2

I don't fully inderstand why you do this:

def go_multi(self, widget, data=None):
    p = Process(target = self.change_textview)
    p.start()
    p.join()

because, even in the remote possibility in which it should work, you're basically calling the change_textview function and waiting for the process to finish.

Cleared this, I don't think you need multiprocessing at all, make your gui multithreading instead.

Make a Gtk multithread may be a little tricky at first, but it's not a difficult task.
You have two ways for doing so:

1. Update your widget using GLib.idle_add (or GObject.idle_add, I never fully understand why sometimes they're not the same)

2. Or follow what's explained [here]. Which it basically says to:

   • Call the following methods before you call Gtk.main():

      GObject.threads_init()
      Gdk.threads_init()
     

   • In your thread, surround the code that updates the Gtk widgets with:

      Gdk.threads_enter()
      # your code here
      Gdk.threads_leave()
     

Answer 3

You must run the main loop to process the rendering events before anything becomes visible.

Also, you must not call GTK functions from a second thread.

Read this to get you started: Multi-threaded GTK applications – Part 1: Misconceptions

And here is how to apply this knowledge to PyGTK: Threads on PyGTK