signalmodule.c uses _PyErr_WriteUnraisableMsg()

[vstinner]

Signal wakeup fd errors are now logged with
_PyErr_WriteUnraisableMsg(), rather than PySys_WriteStderr() and PyErr_WriteUnraisable(), to pass the error message to sys.unraisablehook. By default, it's still written into stderr.

[vstinner]

The change can be tested manually with:

import os
import signal

def sig_alrm(signum, frame):
    print("here")

if True:
    with open(__file__) as fp:
        fd = fp.fileno()
        os.set_blocking(fd, False)
        signal.set_wakeup_fd(fd)
    # fd becomes a bad file descriptor
else:
    a,b=os.pipe()
    os.set_blocking(fd, False)
    fd = a
    signal.set_wakeup_fd(fd)

signal.signal(signal.SIGALRM, sig_alrm)
signal.raise_signal(signal.SIGALRM)
print("exit")