How to block python running using PythonQt

[NessajHu]

There is a part of python script as follows, these functions call C++ functions.

GenerateMesh()
CloseProject()

GenerateMesh start external QProcess to do real task, then return immediatly. It's async. There is another function reciving QProcess::finished signal to do some other work.
CloseProject closes the program.
This design has a fatal problem. GenerateMesh is async, CloseProject is invoked, at this point, the child process is not finished.
A possible solution is move all python operation to subthread, and make GeneratorMesh synchronous. but other function do a lot of UI operation.
Is there a proper way to block or pause python running?

[he-hesce]

There are multiple ways of doing this of course, What solution you prefer depends on how you design and use Qt and object-orientation in general. However, a simply dirty way it so put a wait before CloseProject where you either wait for the QProcess::finished signal emitted from somewhere (so you would need to have it available) or perhaps just do a wait loop like below. The way I usually block until something is finished is this way:

from PythonQt import QtCore
GenerateMesh()
self._waitLoop = QtCore.QEventLoop()
# QtCore.QTimer.singleShot(5000, self._waitLoop.quit)  # Stop waiting after 5 seconds
returnCode = waitLoop.exec_()
self._waitLoop = None
if returnCode == 0:
  CloseProject(True)
else: 
  CloseProject(False)

and then call self._waitLoop.exit(0) either connected to QProcess::finished or from where you handle it. You might of course also want to put a single shot timer on it so make sure you program doesn't hang forever in case QProcess::finished is never signaled - it's in the commented out line above.