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C/Motif on unix: how to pause app while waiting for user response?

I'm trying to implement a reusable function which asks the user for a response, then performs tasks based on the response. The app needs to pause and wait until the response is received, but I can't figure out how to do this without locking up the entire app. In the following example, the Response at line 48 always comes back blank because the run_b routine keeps processing instead of waiting for user_response to complete. Uncommenting the lines at 46.47 causes the entire app to lockup. How can I do this?

#define true 1
#define false 0

#include <Xm/Xm.h>
#include <Xm/MainW.h>
#include <Xm/PushBG.h>
#include <Xm/MessageB.h>

Widget toplevel;
void question_cb (Widget parent, XtPointer client_data, XtPointer call_data);
void run_cb (Widget widget, XtPointer client_data, XtPointer call_data);
void user_response (char *question);
char Response;
int response_valid;

main (int argc, char *argv[])
{
XtAppContext app;
Widget main_window,run_button;

XtSetLanguageProc (NULL, NULL, NULL);
toplevel = XtVaAppInitialize (&app, "App", NULL, 0, &argc, argv, NULL,
                        XmNtitle, "Program Do Something Or Other",
                        XmNwidth, 250,
                        XmNheight, 150,
                        NULL);
main_window = XtVaCreateManagedWidget ("main_window",
                               xmMainWindowWidgetClass, toplevel,
                               NULL);

run_button = XtVaCreateManagedWidget ("Run", xmPushButtonGadgetClass, main_window,
                              XmNtopAttachment, main_window,
                              NULL);
XtAddCallback (run_button, XmNactivateCallback, run_cb, NULL);

XtRealizeWidget (toplevel);

XtAppMainLoop (app);
}

void run_cb (Widget widget, XtPointer client_data, XtPointer call_data)
{
/* process a lot of stuff */

user_response ("Do you want to whatever?");
/* while (!response_valid) {
}*/
printf ("Response = '%c'\n",Response);
if (Response == 'Y') {
/* do some things */
} else {
/* do other things */
}

/* continue processing */
}

void user_response (char *question)
{
Widget dialog;

response_valid = false;
dialog = XmCreateQuestionDialog (toplevel, "notice", NULL, 0);
XtVaSetValues (dialog,
             XmNdialogTitle, XmStringCreateLocalized ("Response"),
             XmNmessageString, XmStringCreateLocalized (question),
             XmNokLabelString, XmStringCreateLocalized ("Yes"),
             XmNcancelLabelString, XmStringCreateLocalized ("No"),
             NULL);
XtAddCallback (dialog, XmNokCallback, question_cb, NULL);
XtAddCallback (dialog, XmNcancelCallback, question_cb, NULL);
XtUnmanageChild (XmMessageBoxGetChild (dialog, XmDIALOG_HELP_BUTTON));
XtManageChild (dialog);
XtPopup (XtParent (dialog), XtGrabNone);
}

void question_cb (Widget parent, XtPointer client_data, XtPointer call_data)
{
XmAnyCallbackStruct *cbs = (XmAnyCallbackStruct *) call_data;

switch (cbs->reason) {
case XmCR_OK :
Response = 'Y';
break;
case XmCR_CANCEL :
Response = 'N';
XtPopdown (XtParent (parent));
break;
case XmCR_ACTIVATE :
break;
case XmCR_HELP :
break;
}
response_valid = true;
}

sunnycoder

Not into Motif so no code from my side but there are a couple of possibilities

1. Fork a new process/thread ... let one process/thread block for user while other does the job

2. Use semaphores or conditional variables ... Suppose func A sets something that func B uses and you dont want to block the rest of the app,
Iitialize a semaphore S to 0

func A ()
{
acquire S if value is 0
do the processing
set S to 1 and continue
}

func B ()
{
acquire S if value is 1
do the processing
set S to 0
continue
}

this will ensure alternation of turns ... You can also use conditional variables if you have more threads in the fray.

griessh

>> user_response ("Do you want to whatever?");

This line only creates the UI part and sets the callbacks.

You are trying to use the wrong programming model. X/Motif is an event driven system. Therefore the action takes place in an event handler. The event handler for your response is "question_cb() " and that's where youi have to deal with the response. If you are planning to create a kind of "GUI library" you have to use the callback function as input paramater for "user_response()"

There is no reason for you to wait for the reply, since X is already taking care of that wait. You provided X with a way to handle the reply by installing the event handler "question_cb() ". This function is only called when (!) the user presses one of the buttons.

=====
Werner

jimdgar

ASKER

Conceptually I understand what you're saying but I still can't see how to implement this. The legacy C code I have is "flow-driven" and depends on getting inputs from the user to make decisions. These inputs cannot be predetermined, they must happen in realtime. In a command-line mode it's easy since the entire app simply waits until the user enters a response to an xterm. Now I want to get the same response from a popup text entry window.

Anyone know of any guidelines on how to do this? I cannot find similar cases in my Motif manuals or online.

ASKER CERTIFIED SOLUTION

griessh

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