Killing sub process that run inside a thread

Question

I'm using python 3.5.3 with PyQT 5 and I have written GUI with it. This GUI run python code python code with subprocess.run.

In order to leave my GUI active and not frozen during the subprocess operation , i'm running the subprocess in a thread.

In the GUI i have stop button that if the user pressed , I want to terminate the subprocess.

I have no problem to kill the thread by using terminate method of the thread. But that's don't terminate the subprocess.

I've tried to use Popen instead of run but I cant make it to run as subprocess.run does. in addition , I prefer to use the recommended way by Python that's give me also the check_error option

This is how I use subprocess:

class c_run_test_thread(QtCore.QThread):

    def __init__(self,test_file,log_file):
        QtCore.QThread.__init__(self)
        self.test_file = test_file
        self.log_file = log_file

    def __del__(self):
        self.wait()

    def run(self):
        # Thread logic

        try:
            # Run the test with all prints and exceptions go to global log file
            self.test_sub_process = subprocess.run(["python", self.test_file],stdout = self.log_file, stderr = self.log_file,check = True)

    except subprocess.CalledProcessError as error:
        print("Error : {}".format(error))

    # Flush memory to file
    self.log_file.flush(

def stop(self):

    # Flush memory to file
    self.log_file.flush()

And I terminate the thread by

# Stop test thread
self.thread_run_test.terminate()

To sum things up , I want to kill thread while killing its sub process too.

Joey Zhang · Accepted Answer · 2017-07-31T17:01:25.950

1

There may be other simpler ways to this, but what I did was to

Use subprocess.Popen to run a sub process, instead of subprocess.run, since the latter will not return before the process is terminated
Check if the process is terminated using Popen.poll
Kill the process using Popen.kill

A sample code would be sth. like the following:

self.test_sub_process = subprocess.Popen(["python", self.test_file],
                                         stdout=self.log_file,
                                         stderr=self.log_file)

Wait for termination:

print("Return code: {}".format(self.test_sub_process.wait()))

Or if you want to do something while waiting:

while self.test_sub_process.poll() is None:
    doSomething()
print("Return code: {}".format(self.test_sub_process.poll()))

Then in thread_run_test.terminate(), you can kill the process

self.test_sub_process.kill()

HTH.

edited Jul 31 '17 at 17:01

answered Jul 30 '17 at 16:01

Joey Zhang

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9

you didn't change the .run to Popen . does it have the same parameters? the PIPE in .run method its nicer than os.read , can I use Popen and PIPE as today and still use Popen? – Gil.I Jul 30 '17 at 21:15
@Gil.I Have changed it to use `Popen`. – Joey Zhang Jul 30 '17 at 22:01
when I used your suggestion , some of the stdout is not written to the log file. I dont know why. Instead I used the following : self.test_sub_process = subprocess.Popen(["python", self.test_file], stdout = self.log_file, stderr = self.log_file) while (self.test_sub_process.poll() is None): print ("Test is running") print("Return code: {}".format(self.test_sub_process.poll())) The return code pare is of course outside of the loop and now the log is full without missing any data – Gil.I Jul 31 '17 at 13:05
@Gil.I, it is interesting that it may lose some `stdout` messages. Does `self.test_file` write to both `stderr` and `stdout`? I believe they should be handled differently. Anyway, it looks like it is more convenient for you to just use file objects instead of `PIPE`s. I've updated the response to meet your situation better. – Joey Zhang Jul 31 '17 at 17:01
I posted a followup question ,to know how to kill the subprocess in orderly fashion , while calling all objects destrcutors https://stackoverflow.com/questions/45422527/how-to-kill-sub-process-in-anytime-while-closing-it-in-orderly-fashion – Gil.I Jul 31 '17 at 18:09

Killing sub process that run inside a thread

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