}

    switch (option) {
    case THREAD_CANCEL: {
	Tcl_WideInt id;
	const char *result;
	int flags;
	size_t arg;

	if ((objc < 3) || (objc > 5)) {
	    Tcl_WrongNumArgs(interp, 2, objv, "?-unwind? id ?result?");
	    return TCL_ERROR;
	}
	flags = 0;
	arg = 2;

    char buf[TCL_DOUBLE_SPACE+1];

    snprintf(buf, sizeof(buf), "%p", Tcl_GetCurrentThread());

    errorInfo = Tcl_GetVar2(interp, "errorInfo", NULL, TCL_GLOBAL_ONLY);
    if (errorProcString == NULL) {
	errChannel = Tcl_GetStdChannel(TCL_STDERR);
	Tcl_WriteChars(errChannel, "Error from thread ", TCL_INDEX_NONE);
	Tcl_WriteChars(errChannel, buf, TCL_INDEX_NONE);
	Tcl_WriteChars(errChannel, "\n", 1);
	Tcl_WriteChars(errChannel, errorInfo, TCL_INDEX_NONE);
	Tcl_WriteChars(errChannel, "\n", 1);
    } else {
	argv[0] = errorProcString;
	argv[1] = buf;
	argv[2] = errorInfo;
	script = Tcl_Merge(3, argv);
	ThreadSend(interp, errorThreadId, script, 0);

     * Since Tcl_CancelEval can be safely called from any thread,
     * we do it now.
     */

    Tcl_MutexUnlock(&threadMutex);
    Tcl_ResetResult(interp);
    return Tcl_CancelEval(tsdPtr->interp,
    	(result != NULL) ? Tcl_NewStringObj(result, TCL_INDEX_NONE) : NULL, 0, flags);
}

/*
 *------------------------------------------------------------------------
 *
 * ThreadEventProc --
 *