Attaching to a running program

It is possible to remotely start the debugger for a program running on the same computer.

Basics

Use the fgldb command with the -p option to switch the runtime system into debug mode when an application is running on a server.

Note: The fgldb command must be executed on the machine where the fglrun process executes.

The fgldb command line tool takes the fglrun process id as value for the -p argument.

Note: Before starting a debug session, make sure that you fulfill the prerequisites for debugging.

Debug a program running on a UNIX server

First, identify the process id of the fglrun program running on your server.

For example, on a UNIX® platform, use the ps command:

$ ps a | grep fglrun
10646 pts/0    S+     0:00 /opt/myapp/fgl/lib/fglrun stockinfo.42m

Note: Inspect the GAS log files to find the id of a fglrun process running behind a GAS application server. Enable full log reports in the GAS to get detailed information about process execution.

You may want to debug processes that use a lot of machine resources (processor, memory or open files). Use a system utility to find a process id by resources used (for example, the top command on Linux®).

Execute the fgldb tool with the process id of the program you want to attach to:

$ fgldb -p 10646
108	    DISPLAY ARRAY contlist TO sr.*
(fgldb)

The (fgldb) prompt indicates that you are now connected to the fglrun process, and the program flow is suspended. To continue with the program flow, enter the "continue" debugger command:

(fgldb) continue
Continuing.

The application will then resume. To suspend the program again and enter debugger commands, press CTRL-C in the debug console. fgldb will display the interrupt message and return control to the debugger:

...
Continuing.
^CINTERRUPT
108	    DISPLAY ARRAY contlist TO sr.*
(fgldb)

At this point, you can enter debugger commands. For example, set a break point and continue until the break point is reached:

(fgldb) b 427
Breakpoint 2 at 0x00000000: file contacts.4gl, line 427.
(fgldb) continue 
Continuing.
Breakpoint 2, edit_contact() at contacts.4gl:427
427	    IF new THEN
(fgldb)

To finish the debug session, close the connection with the "detach" debugger command:

(fgldb) detach
Connection closed by foreign host.