HP 3000 Manuals HP 3000 Manuals
Debugging Threaded Applications
The following are hints for debugging threaded applications:
* Set breakpoints for global data bugs - To simplify debugging
problems involving unexpected changes in global data, use HPDEBUG
to set task-wide data breakpoints. Otherwise, make sure there is
a breakpoint that every thread will hit. Even when you are
single-stepping, another thread can intervene between source
statements executed by the thread you are following. One way you
can know that this is happening is if the intervening thread hits
a breakpoint.
You can prevent other threads from interveining while single
stepping in HPDEBUG. This is done by setting the HPDEBUG
environment variable SS_TERM_KEEPLOCK. Setting this variable
causes you to hold the terminal semaphore for the current thread
until a CONTINUE command is issued. Effectively, no other thread
is able to obtain the terminal semaphore and interfere with your
debug session. Another method is to create breakpoints within
your task that have the "Stop-all-Threads" options. This option,
when hit by any thread in the task, stops execution of all threads
in the task until a CONTINUE command is issued. It is possible to
create a deadlock situation when using SS_TERM_KEEPLOCK with
"Stop-all-Threads" set in your task.
* Debugging a threaded server - Do not debug multiple threads in the
server, debug one at a time. To do this, set a breakpoint at the
procedure you want to catch and continue. Then make only one
remote procedure call from the client; you will hit the
breakpoint, step through until you locate the bug, then continue
or quit.
* Debugging a threaded client - If the threads in a client do not
interact, debug only one of them at a time.