[Python-Dev] The zombi thread of the Tcl library (original) (raw)

Victor Stinner victor.stinner at haypocalc.com
Wed May 4 10:58:42 CEST 2011

Hi,

I have a question: would it be possible to mask all signals in the Tcl thread? To understand the question, let's see the context...

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 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.)

Victor

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