Debug Tutorial: Instructions for Example

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Starting debug

• Change your directory so that you are present in the directory where the example executable is located.
• Start debug on eight nodes:
  debug -sz 8 galaxyf
• debug should come up, pause while loading the processes, and then display the debug prompt containing the default context.
• If the source files for the example are in a different directory, add that directory to the source search path list with the use command:
  use + galaxy

• The context defines the set of processes to which a command is applied. The default context displayed in the prompt can be changed by issuing the context command with a new context argument. Change the context to include only 1 process and then change it back again:
  context(1)
  context(all)
• Most commands allow a context specification which causes the context to change only for the single command.
• The state of the processes can be determined using the process command. Display the state of the processes immediately after loading:
  process

• A line numbered source code listing is given by the list command. You can see the line you are currently stopped at by entering:
  list
  
• Entering list again will continue listing from where the previous list left off:
  list
  
• Now list the lines where we will be setting some breakpoints:
  list 40
  
• Set breakpoints on lines 44, 46, and 48 using the stop command as follows:
  stop 44; stop 46; stop 48
  
• Use the status command to confirm the breakpoints are set:
  status
  
• Now execute the program with the cont command as follows:
  cont;wait
  
• Note the use of the wait command in conjunction with cont which allows any program terminal I/O to occur.
• Shortly, a process state display will appear (caused by the wait) which shows processes stopped at lines 44, 46, and 48.
• The context indicates which processes' are stopped at each breakpoint.

• The contents of a variable is displayed using the print command. Print the value of a variable:
  print my_node
  
• The data values are unique for each process, so each is listed separately.
• Print the first 5 elements of the receive buffer array:
  print recvLeft.fMessage,10
  
• In this case the data values are the same across all of the nodes so a single list is displayed.

• Set a breakpoint on the message receive call in form.c procedure Form() at line 20:
  stop `form`20
  
• Resume execution of the program:
  cont;wait
  
• After waiting awhile, you realize the program is taking longer than expected to reach the breakpoint. Interrupt the wait command:
  <Ctrl-C>
  
• Check the state of the processes:
  process
  
• Note that processes 2, 4, and 6 (for eight process load) have hit the breakpoint while the other processes remain in the Executing state.
• Stop these processes with the halt command:
  halt
  
• The previously Executing processes should now be in the Interrupted state as seen with the process command:
  process
  

• The call stack is displayed with the where command:
  where
  
• You can now determine that the processes you halted are stopped within a routine that reflects a blocking receive was in progress.
• You can view the source code for a particular function of interest (e.g. to see the blocking call):
  list Form
  
• Note that a window of lines is displayed in this case.

• Information about receives in progress is displayed with the recvqueue command:
  recvqueue
  
• Pending message information is viewed using the sendqueue command:
  sendqueue
  

• You can allow the program to finish executing at this point or simply exit the debugger. To finish the execution, remove all of the breakpoints using the delete command and continue the program:
  delete all
  cont; wait
  
• To terminate the program and exit the debugger use the quit command (or exit):
  quit