How can I gracefully handle SIGTERM signals in Python for smooth process termination?

Handling SIGTERM Signals for Graceful Process Termination

In the context of managing daemon processes in Python, handling SIGTERM signals gracefully is crucial to ensure orderly shutdown. When a SIGTERM signal is received, the default behavior is for the program to terminate immediately, potentially disrupting critical operations.

To prevent abrupt termination, it's essential to handle SIGTERM signals appropriately. One approach involves using the signal.signal function to register a handler for the signal. However, this handler will still interrupt the current execution flow and take control.

For more refined signal handling, consider using a separate thread or process to manage the signal. This decouples the handling process from the main execution, allowing the program to continue its operations while the signal is handled asynchronously.

One common technique involves creating a flag (e.g., shutdown_flag) that is set to True when the SIGTERM handler is triggered. The main loop can periodically check the flag to gracefully terminate the process when shutdown_flag is set.

Below is an example demonstrating how to implement a clean solution using a class:

import signal
import time

class GracefulKiller:
    kill_now = False  # Flag to indicate termination

    def __init__(self):
        # Register SIGTERM and SIGINT handlers to set kill_now
        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()
    # Main loop that continues until kill_now is set to True
    while not killer.kill_now:
        time.sleep(1)
        print("Doing something in a loop...")
    
    print("End of the program. I was killed gracefully :)")

This script creates a GracefulKiller class that handles SIGTERM and SIGINT signals. When either signal is received, the kill_now flag is set to True. The main loop periodically checks this flag and gracefully terminates when kill_now becomes True.

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