XDebug Tutorial: Instructions for Example

This example session will introduce you to various parts of xdebug.

You must first collect the example source files and Makefile and build the executable galaxyf. This example code is a small demonstration program that does NX message passing.

Starting xdebug

Change your directory so that you are present in the directory where the example source files and executable are.
Start xdebug on eight nodes:
xdebug -sz 8 galaxyf
xdebug should come up, pause while loading the processes, and then switch to the process page.
Note: If an error occurred during the load, switch to the input/output page to see the error message.

Notebook design

The main notebook contains pages of major debugging activity.
Clicking on a tab, or using the View menu, displays specific pages in the notebook.
Notebook pages can be torn out into dialogs in case you want to display more than one page at a time.
Switch to the process page.
Click on the vertical dashed line.
Process page now in own dialog that can be moved around.
Click on the vertical dashed line within the process page dialog to return to the main notebook.

Viewing Source and Setting Breakpoints

Switch to the source page.
Click on the routine main within the file main.c

Scroll down so that lines 44, 46, and 48 are visible. Should look like:

 43:     if ( my_node == 0)
 44:         Create();
 45:     else if ( my_node == (num_nodes - 1))
 46:         Collapse();
 47:     else
 48:         Form();

Click on the triangle next to the three lines so that a breakpoint is set for 44, 46, and 48.
Pull down the Execute menu and select Continue.
Shortly, three checkmarks should appear next to 44, 46, and 48. This means at least one process is stopped at each of these lines.
Switch to the process page and verify that each process is indeed at a break point.
Move cursor over each process to see message summary of process' state and location.

Diving into Source Code Contents

Switch to the source page.
Move the pointer over line 44's call to Create() and use mouse button number two to click on Create().
Source code to Create() should be displayed.
Pull down the history menu and select main.c at main.
Move the pointer over the variable my_node and click again with mouse button number two.
Display should switch the the data page and automatically display the value of my_node for all the processes in context.

Forcing Message Blocking Situation

Switch to the source page.
Select the routine Form under file form.c
Set a break point on line 20 by clicking next to the line. Line 19 and 20 should look like:
```
19:         {
20:         crecv( 0, &recvLeft, sizeof( TMessage));
```
Switch to the process page.
Select the Continue button.
Note that processes 2, 4, and 6 (for eight process load) have hit the breakpoint while the other processes remain within the Executing state.
Select the Halt button.
The previously Executing processes should now be in the Blocked state. This means they are stopped within a routine that reflects a blocking receive is in progress.

Viewing the Stack

Switch to the stack page.
Select the Update button.
A graphical representation of the call stack should appear.
Colored nodes represent places where processes are stopped.
The Call Graph button provides names for the call-graph elements.
Clicking on a colored button presents a dialog with a listing of the processes at that point.
Tip: If you want wider nodes in your stack frame, change the following line in your .Xdefaults or XDebug resource file:
XDebug*CallGraphButton.width: 72
to be use a value greater than 72.

Viewing the Message Queue

Switch to the message queue page.
Select the Update button.
Information about receives in progress is displayed in a colored grid.
Select radio button Messages Pending Receipt.
Pending message information is now present, too.
Moving cursor over a colored box displays process number.
Clicking on a colored box displays queue information for process.

Exiting XDebug

Choose Exit from the File menu.
After a brief pause, xdebug's window will vanish.

Intel Tutorial Notes

Acknowledgement and Disclaimer