New submission from Masahiro Sakai <[email protected]>:
If I run following program, the parent process fails with "RecursionError:
maximum recursion depth exceeded", because the signal handler is invoked during
the execution of the same handler.
----
import os
import signal
import time
def f(signum, frame):
time.sleep(1)
signal.signal(signal.SIGUSR1, f)
parent_pid = os.getpid()
child_pid = os.fork()
if child_pid == 0:
for i in range(100000):
os.kill(parent_pid, signal.SIGUSR1)
time.sleep(0.01)
else:
os.waitpid(child_pid, 0)
----
This behavior is in contrast to other languages such as C or Ruby.
In C, when a handler function is invoked on a signal, that signal is
automatically blocked during the time the handler is running, unless SA_NODEFER
is specified.
In Ruby, signal handler is handled in a way similar to Python (i.e. flag is set
by C-level signal handler and Ruby/Python-level signal handler is executed
later point which is safe for VM), but it prevents recursive signal handler
invocation. (Related issue and commit: https://bugs.ruby-lang.org/issues/6009
https://github.com/ruby/ruby/commit/6190bb4d8ad7a07ddb1da8fc687b20612743a34a )
I believe that behavior of C and Ruby is desirable, because writing reentrant
signal handler is sometimes error prone.
----------
components: Extension Modules
messages: 362562
nosy: msakai
priority: normal
severity: normal
status: open
title: Signal handler is invoked recursively
type: behavior
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Python tracker <[email protected]>
<https://bugs.python.org/issue39735>
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