PyQt UI Development for Maya - Chapter 03 - blocking/non-blocking operations

blocking.py

#!/usr/bin/env python

"""
Copyright (c) 2012, Justin Israel (justinisrael@gmail.com) 
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   used to endorse or promote products derived from this software without 
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blocking.py 

Chapter03 - Blocking the UI

An example of how one should avoid blocking the main 
GUI thread, and make use of signal/slot notifications.
"""

import sys
import subprocess

from PyQt4 import QtCore, QtGui

## adjust the sleep shell command for windows platform
import platform 
if platform.system() == "Windows":
	SLEEP_CMD = ['python', '-c', 'import time\ntime.sleep(5)']
else:
	SLEEP_CMD = ['sleep', '5']

class BlockingTest(object):

	def main(self):

		app = QtGui.QApplication(sys.argv)

		self.win = QtGui.QWidget()
		self.win.resize(300,200)

		layout = QtGui.QVBoxLayout(self.win)

		blocking_button = QtGui.QPushButton("Block")
		blocking_button.clicked.connect(self.blocking)
		layout.addWidget(blocking_button)

		signal_button = QtGui.QPushButton("Signals")
		signal_button.clicked.connect(self.non_blocking)
		layout.addWidget(signal_button)

		self.output = QtGui.QLineEdit()
		layout.addWidget(self.output)

		clear_button = QtGui.QPushButton("Clear")
		clear_button.clicked.connect(self.output.clear)
		layout.addWidget(clear_button)

		self.win.show()
		self.win.raise_()

		app.exec_()


	def finished(self, returnCode):
		self.setMessage("Return code: %s" % returnCode)


	def setMessage(self, msg):
		print msg
		self.output.setText(msg)		


	def blocking(self):
		self.setMessage("Starting blocking sleep")

		# process = subprocess.Popen(['sleep', '5'])
		process = subprocess.Popen(SLEEP_CMD)
		ret = process.wait()
		self.finished(ret)


	def non_blocking(self):
		self.setMessage("Starting non blocking sleep")

		process = QtCore.QProcess(parent=self.win)
		process.setProcessChannelMode(process.ForwardedChannels)
		process.finished.connect(self.finished)
		# process.start('sleep', ['5'])
		process.start(SLEEP_CMD[0], SLEEP_CMD[1:])


if __name__ == "__main__":
	app = BlockingTest()
	app.main()