180. Signal Handling with signal Module

Snippet 1: Basic Signal Handling

import signal
import sys

def signal_handler(signum, frame):
    print(f"Signal {signum} received")
    sys.exit(0)

# Handle SIGINT (Ctrl+C)
signal.signal(signal.SIGINT, signal_handler)

print("Press Ctrl+C to exit.")
signal.pause()  # Wait for signals

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Snippet 2: Handling SIGTERM (Termination Signal)

import signal
import sys

def signal_handler(signum, frame):
    print(f"Received termination signal: {signum}")
    sys.exit(0)

# Handle SIGTERM (kill command)
signal.signal(signal.SIGTERM, signal_handler)

print("Waiting for termination signal...")
signal.pause()  # Wait for signals

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Snippet 3: Custom Signal Handler with Arguments

import signal

def signal_handler(signum, frame):
    print(f"Signal {signum} received at frame {frame}")

# Handle SIGUSR1 (User-defined signal 1)
signal.signal(signal.SIGUSR1, signal_handler)

print("Send SIGUSR1 to this process to trigger the handler.")
signal.pause()  # Wait for signals

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Snippet 4: Ignoring Signals

import signal

# Ignore the SIGINT signal (Ctrl+C)
signal.signal(signal.SIGINT, signal.SIG_IGN)

print("Press Ctrl+C, but it will be ignored.")
signal.pause()  # Wait for signals

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Snippet 5: Raising a Signal Programmatically

import signal
import os

def signal_handler(signum, frame):
    print(f"Signal {signum} received")

# Handle SIGUSR2 (User-defined signal 2)
signal.signal(signal.SIGUSR2, signal_handler)

# Send SIGUSR2 to the current process
os.kill(os.getpid(), signal.SIGUSR2)

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Snippet 6: Setting a Timeout with SIGALRM

import signal
import time

def timeout_handler(signum, frame):
    print("Timeout reached!")
    exit(1)

# Handle SIGALRM (alarm signal)
signal.signal(signal.SIGALRM, timeout_handler)

# Set an alarm to trigger after 5 seconds
signal.alarm(5)

print("Waiting for alarm...")
time.sleep(10)  # Wait to see if the alarm triggers

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Snippet 7: Handling Multiple Signals

import signal
import sys

def signal_handler(signum, frame):
    print(f"Signal {signum} received")
    sys.exit(0)

# Handle multiple signals (SIGINT and SIGTERM)
signal.signal(signal.SIGINT, signal_handler)
signal.signal(signal.SIGTERM, signal_handler)

print("Press Ctrl+C or send a SIGTERM to exit.")
signal.pause()  # Wait for signals

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Snippet 8: Re-setting a Signal Handler

import signal

def first_handler(signum, frame):
    print("First handler triggered")

def second_handler(signum, frame):
    print("Second handler triggered")

# Set the first handler for SIGINT
signal.signal(signal.SIGINT, first_handler)

# Trigger the first handler
signal.raise_signal(signal.SIGINT)

# Re-set the signal handler to the second handler
signal.signal(signal.SIGINT, second_handler)

# Trigger the second handler
signal.raise_signal(signal.SIGINT)

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Snippet 9: Using signal.pause() for Blocking

import signal

def signal_handler(signum, frame):
    print(f"Received signal {signum}")

# Handle SIGINT
signal.signal(signal.SIGINT, signal_handler)

print("Waiting for signal...")
signal.pause()  # Wait indefinitely for a signal

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Snippet 10: Handling Signals in a Separate Thread

import signal
import threading
import time

def signal_handler(signum, frame):
    print(f"Signal {signum} received")

def signal_thread():
    # Handle SIGINT
    signal.signal(signal.SIGINT, signal_handler)
    signal.pause()

# Start a thread to handle signals
thread = threading.Thread(target=signal_thread)
thread.start()

# Main thread sleeps to simulate work
time.sleep(5)
print("Main thread exiting")

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