tkinter runs a busy-wait loop on interactive Python

Bug report

Bug description:

In EventHook in Modules/_tkinter.c, we used to have the following block to run the event loop:

#if defined(WITH_THREAD) || defined(MS_WINDOWS)
        Py_BEGIN_ALLOW_THREADS
        if(tcl_lock)PyThread_acquire_lock(tcl_lock, 1);
        tcl_tstate = event_tstate;
        
        result = Tcl_DoOneEvent(TCL_DONT_WAIT);
        
        tcl_tstate = NULL;
        if(tcl_lock)PyThread_release_lock(tcl_lock);
        if (result == 0)
            Sleep(Tkinter_busywaitinterval);
        Py_END_ALLOW_THREADS
#else
        result = Tcl_DoOneEvent(0);
#endif

in bpo-31370, support for threads-less builds was removed, and this block became

        Py_BEGIN_ALLOW_THREADS
        if(tcl_lock)PyThread_acquire_lock(tcl_lock, 1);
        tcl_tstate = event_tstate;
        
        result = Tcl_DoOneEvent(TCL_DONT_WAIT);
        
        tcl_tstate = NULL;
        if(tcl_lock)PyThread_release_lock(tcl_lock);
        if (result == 0)
            Sleep(Tkinter_busywaitinterval);
        Py_END_ALLOW_THREADS

This is a bit unfortunate, as we now back to running a busy-wait loop. See Guido van Rossum's comment of May 23, 1998: 7bf15648

I guess this block could be

        if (self->threaded) {
            /* Allow other Python threads to run. */
            ENTER_TCL
            result = Tcl_DoOneEvent(0);
            LEAVE_TCL
        }
        else {
            Py_BEGIN_ALLOW_THREADS
            if(tcl_lock)PyThread_acquire_lock(tcl_lock, 1);
            tcl_tstate = tstate;
            result = Tcl_DoOneEvent(TCL_DONT_WAIT);
            tcl_tstate = NULL;
            if(tcl_lock)PyThread_release_lock(tcl_lock);
            if (result == 0)
                Sleep(Tkinter_busywaitinterval);
            Py_END_ALLOW_THREADS
        }

in analogy with the event loop in _tkinter_tkapp_mainloop_impl. As self->threaded is true in most builds, this would avoid the busy-wait loop.

I am happy to submit a PR, but I'll wait until PR #140147 is in to avoid unnecessary complications to this code.

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

Commencez dans Modules/_tkinter.c, au niveau de EventHook, et comparez son bloc de boucle d’événements avec _tkinter_tkapp_mainloop_impl. Consultez PR #140147 avant de modifier ce code. Le travail est terminé lorsque Python interactif évite la boucle d’attente active dans les builds avec threads tout en conservant le comportement non threadé montré.