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Author vstinner
Recipients aldwinaldwin, asvetlov, docs@python, eric.snow, fabioz, int19h, ncoghlan, pitrou, tim.peters, vstinner
Date 2019-07-04.10:19:46
SpamBayes Score -1.0
Marked as misclassified Yes
Message-id <>
Python internals already know who is the "main" thread: _PyRuntime.main_thread. It's maintained up to date, even after a fork, PyOS_AfterFork_Child() calls _PyRuntimeState_ReInitThreads() which does:

    // This was initially set in _PyRuntimeState_Init().
    runtime->main_thread = PyThread_get_thread_ident();

I already added _thread._is_main_interpreter() to deny spawning daemon threads in subinterpreters: bpo-37266.

We can add _thread._is_main_thread() which can reuse Modules/signalmodule.c code:

static int
is_main(_PyRuntimeState *runtime)
    unsigned long thread = PyThread_get_thread_ident();
    PyInterpreterState *interp = _PyRuntimeState_GetThreadState(runtime)->interp;
    return (thread == runtime->main_thread
            && interp == runtime->interpreters.main);

For example, this function is used by signal.signal:

    if (!is_main(runtime)) {
                        "signal only works in main thread");
        return NULL;
Date User Action Args
2019-07-04 10:19:47vstinnersetrecipients: + vstinner, tim.peters, ncoghlan, pitrou, fabioz, asvetlov, docs@python, eric.snow, aldwinaldwin, int19h
2019-07-04 10:19:46vstinnersetmessageid: <>
2019-07-04 10:19:46vstinnerlinkissue31517 messages
2019-07-04 10:19:46vstinnercreate