Dead code in tkinter

[mdehoon]

Bug report

Bug description:

Modules/_tkinter.c always defines TCL_THREADS:

/* If Tcl is compiled for threads, we must also define TCL_THREAD. We define
   it always; if Tcl is not threaded, the thread functions in
   Tcl are empty.  */ 
#define TCL_THREADS

but in two places in Modules/_tkinter.c , we check if TCL_THREADS is defined:

#ifdef TCL_THREADS
static Tcl_ThreadDataKey state_key;
typedef PyThreadState *ThreadSpecificData;
#define tcl_tstate \
    (*(PyThreadState**)Tcl_GetThreadData(&state_key, sizeof(PyThreadState*)))
#else
static PyThreadState *tcl_tstate = NULL;
#endif

and

#ifndef TCL_THREADS
    if (v->threaded) {
        PyErr_SetString(PyExc_RuntimeError,
                        "Tcl is threaded but _tkinter is not");
        Py_DECREF(v);
        return 0;
    }
#endif

Especially the latter is confusing, as this code block is not compiled and the test is never executed.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-140494: require that Tcl is built with thread support #141241
• gh-140494: Remove dead code ifndef TCL_THREADS, which is always defined #152841

[terryjreedy]

tcl/tk 8.5 was by default compiled without thread_support. 8.6 by default is, and perhaps the option is gone. Thread support was once optional in python, but now is mandatory so _tkinter should support them also.

I suspect that the define and the comment before could be eliminated (if these are the only two uses) and the code between #ifdef TCL_THREADS and #ELSE# made unconditional and the other code eliminated. @serhiy-storchaka ?

[serhiy-storchaka]

It was unconditionally enabled in b5bfb9f, 23 years ago. Well, I think we can remove this code now. Note that some comments may be need to be updated.

[mdehoon]

We still need to #define TCL_THREADS , otherwise tkinter won't compile.

Should we require that tcl/tk was compiled with thread support, or should we still allow tcl/tk without thread support?