import os
import signal
import sys
import time
import threading


def mysleep(delay):
    start = time.monotonic()
    time.sleep(delay)
    dt = time.monotonic() - start
    if dt < delay:
        print("sleep was interrupted! thread %s" % threading.current_thread().ident)


def sighandler(signum, frame):
    text = 'Python signal handler, thread %s\n' % threading.current_thread().ident
    # don't use print() to avoid reentrant lock issue in io.TextIOWrapper()
    os.write(sys.stdout.fileno(), text.encode())
    raise Exception


def worker():
    print("thread: wait")
    mysleep(5)
    print("thread: done")


def main():
    print("main: main thread %s" % threading.current_thread().ident)

    signal.signal(signal.SIGUSR1, sighandler)

    t = threading.Thread(target=worker)
    t.start()
    print("main: spawn thread %s" % t.ident)

    print("main: sleep")
    mysleep(1)

    print("main: send signal to thread")
    signal.pthread_kill(t.ident, signal.SIGUSR1)

    print("main: sleep again")
    mysleep(1)

    print("main: wait thread")
    t.join()
    print("main: done")


if __name__ == '__main__':
    main()