raise_signal docs imply process receives signal not thread

Documentation

The documentation of signal.raise_signal(signum) is:

Sends a signal to the calling process

Which somewhat implies the signal is sent to the main thread of the process, ie. equivalent to os.kill(os.getpid(), signum). In actuality the signal is sent to the calling thread, which with the nuance of how Python executes signal handlers can lead to subtly different behaviour with regard to interrupting blocking functions.

The attached example shows how this interpretation can lead to bugs.

$ python example.py kill
Waiting for signal...
Handling signal 15
Wait interrupted by signal

$ python example.py raise_signal
Waiting for signal...

example.py

import os
import signal
import sys
import threading
import time

# Register a handler to flag an event when a signal is received
signalled_flag = threading.Event()


def signal_handler(signum, _frame):
    print(f"Handling signal {signum}")
    signalled_flag.set()


signal.signal(signal.SIGTERM, signal_handler)


# Raise the signal in a separate thread once the main thread is waiting on said event
def do_raise_signal():
    time.sleep(0.01)
    signal.raise_signal(signal.SIGTERM)


def do_kill_process():
    time.sleep(0.01)
    os.kill(os.getpid(), signal.SIGTERM)


match sys.argv:
    case [_, "raise_signal"]:
        thread = threading.Thread(target=do_raise_signal)
    case [_, "kill"]:
        thread = threading.Thread(target=do_kill_process)
    case _:
        print(f"Usage: {sys.argv[0]} [raise_signal|kill]")
        sys.exit(1)


thread.start()

# Wait for the signal to be received
print("Waiting for signal...")
signalled_flag.wait()
print("Wait interrupted by signal")

Linked PRs

• gh-129167

從 signal.raise_signal(signum) 的文件項目開始，閱讀連結的訊號與執行緒指南。明確說明訊號會傳送至呼叫執行緒，而不是暗示訊號會傳送至程序或主執行緒，然後確認文件措辭與範例仍然保持一致。