Debugging a PVM program

Debugging parallel programs is much more difficult than debugging serial programs
- There are more processes running simultaneously
- Their interaction can occur error
Deadlock: a programming error has caused all the processes to be waiting on messages
Resource failure: due to an error, processes have spawned extra processes
All PVM routines returns an error condition if some error has been detected during their execution
Two routines pvm_perror() and pvm_setopt (PvmAutoErr...) are provided to allow the detection and printing of any PVM error

Spawned PVM tasks can also be started under a debugger
- By setting the flag option to include PvmTaskDebug in pvm_spawn()
- By setting the -? option of the spawn instruction under the console

PVM will execute the shell script pvm3/lib/debugger:

pvm3/lib/debugger pvm3/bin/ARCH/a.out arg1 arg2 ...

As supplied, this script
- Starts an xterm window on the host PVM was started
- Spawns the task under a debugger in this window
The shell script can be modified to include a favorite debugger or to do something else.

The following one-liner times each spawned a.out:
```
/bin/time "$@" 2>> $HOME/time.out
        
```

Diagnostic print statement sent to either stdout or stderr from a spawned task will not appear on the user's screen

Use pvm_catchout () to do it
All these prints are routed to a single log file
/tmp/pvml.<uid>
on the host where PVM was started