Question

I have a script that does a bunch of things and I want to spawn a thread that monitors the cpu and memory usage of what’s happening.

The monitoring portion is:

import psutil
import time
import datetime

def MonitorProcess():
    procname = "firefox"

    while True:
            output_sys = open("/tmp/sysstats_counter.log", 'a')

            for proc in psutil.process_iter():
                    if proc.name == procname:
                            p = proc

            p.cmdline

            proc_rss, proc_vms =  p.get_memory_info()
            proc_cpu =  p.get_cpu_percent(1)

            scol1 = str(proc_rss / 1024)
            scol2 = str(proc_cpu)

            now = str(datetime.datetime.now())

            output_sys.write(scol1)
            output_sys.write(", ")
            output_sys.write(scol2)
            output_sys.write(", ")
            output_sys.write(now)
            output_sys.write("\n")

            output_sys.close( )

            time.sleep(1)

I’m sure there’s a better way to do the monitoring but I don’t care at this point.

The main script calls:

RunTasks() # which runs the forground tasks 
MonitorProcess() # Which is intended to monitor the tasks CPU and Memory Usage over time

I want to run both functions simultaneously. To do this I assume that I have to use the threading library. Is the approach then to do something like:

thread = threading.Thread(target=MonitorProcess())
thread.start

Or am I way off?

Also when the RunTasks() function finishes how do I get MonitorProcess() to automatically stop? I assume I could test for the process to be present and if it’s not kill the function???

Answer 1

It sounds like you want a daemon thread. From the docs:

A thread can be flagged as a “daemon thread”. The significance of this flag is that the entire Python program exits when only daemon threads are left. The initial value is inherited from the creating thread. The flag can be set through the daemon property.

In your code:

thread = threading.Thread(target=MonitorProcess)
thread.daemon = True
thread.start()

The program will exit when main exits, even if the daemon thread is still active. You will want to run your foreground tasks after you set up and start your monitoring thread.