Can Python Processes Handle SIGTERM Gracefully Without Interruption?

Handling SIGTERM for Graceful Shutdown

In the context of real-world applications, it is essential to ensure that processes can handle termination signals gracefully to prevent abrupt interruptions. In Python, the handling of SIGTERM (TERM) is a common requirement when managing daemon processes.

Consider the following example Daemon process:

def mainloop():
    while True:
        # Important operations
        # ...
        # Sleep

Problem:

When the Daemon process receives a SIGTERM signal by default, the execution flow is interrupted immediately, leading to the termination of the process without completing ongoing operations.

Question:

Is it possible to handle SIGTERM gracefully without interrupting the current execution flow? The goal is to allow the process to finish the current operation and then exit gracefully by setting a shutdown flag within a separate thread.

Solution:

Using a Graceful Killer Class:

We can leverage a simple GracefulKiller class to handle SIGTERM gracefully:

import signal
import time

class GracefulKiller:
    kill_now = False

    def __init__(self):
        signal.signal(signal.SIGINT, self.exit_gracefully)
        signal.signal(signal.SIGTERM, self.exit_gracefully)

    def exit_gracefully(self, signum, frame):
        self.kill_now = True

if __name__ == '__main__':
    killer = GracefulKiller()
    while not killer.kill_now:
        time.sleep(1)
        print("Performing operation...")

    print("Process exited gracefully.")

In this solution:

1. The GracefulKiller class sets up signal handlers for SIGINT (Ctrl C) and SIGTERM (sent by default by start-stop-daemon).
2. The exit_gracefully method is executed when either signal is received. It sets the kill_now flag to True.
3. The main loop continuously checks the kill_now flag. If it's True, it signifies that a signal has been received, and the process gracefully exits.
4. This approach allows the main loop to complete its current operation before the process exits, preventing abrupt termination.

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