[issue11998] test_signal cannot test blocked signals if _tkinter is loaded

[STINNER Victor]

New submission from STINNER Victor <victor.stinner at haypocalc.com>:

I'm working on signals, especially on pthread_sigmask(), and I'm trying to understand test_signal failures.

test_signal fails if the _tkinter module is loaded, because _tkinter loads the Tcl library which create a thread waiting events in select(). For example, "python -m test test_pydoc test_signal" fails, because test_pydoc loads ALL Python modules. I opened an issue for test_pydoc: http://bugs.python.org/issue11995

_tkinter.c contains the following code:
#if 0
    /* This was not a good idea; through <Destroy> bindings,
       Tcl_Finalize() may invoke Python code but at that point the
       interpreter and thread state have already been destroyed! */
    Py_AtExit(Tcl_Finalize);
#endif

Tcl_Finalize() exits the thread, but this function is never called in Python. Anyway, it is not possible to unload a module implemented in C.

I would like to know if it would be possible to mask all signals in the Tcl thread, or if Tcl supports/uses signals.

It is possible to mask all signals in the Tcl thread using:
----------
allsignals = range(1, signal.NSIG)
oldmask = signal.pthread_sigmask(signal.SIG_BLOCK, allsignals)
import _tkinter
signal.pthread_sigmask(signal.SIG_SETMASK, oldmask)
----------

I'm not asking the question for test_signal: I have a patch fixing test_signal, even if the Tcl zombi thread is present (use pthread_kill() to send the signal directly to the main thread).

(I wrote "zombi" thread because I was not aware that Tcl uses a thread,
nor that test_pydoc loads all modules. The thread is valid, alive, and
it's just a joke. The threads is more hidden than zombi.)

(Message copied/pasted from python-dev)

----------
components: Tests, Tkinter
messages: 135109
nosy: haypo
priority: normal
severity: normal
status: open
title: test_signal cannot test blocked signals if _tkinter is loaded
versions: Python 3.3

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