Very Computer

Hello all,

Consider the following situation:

A parent process allocates a set of semaphores. It then begins to
spawn children (which use the semaphores). The semaphores are
a global resource and so need to be explicitly destroyed; however
if a *child* process destroys them accidentally then things could
get *. So the question becomes: where is the best place to
clean up?

There seem to be two places to put cleanup code: in exit
procedures, which are installed using atexit(), and in signal
functions. In the code that I am patching, the signal functions
for SIGTERM, SIGTRAP, SIGQUIT and SIGINT etc all call
exit() and so atexit() would seem like a good idea. However,
I think I am correct in saying that both signal handlers and
exit procedures are inherited by child processes.

I *could* do the following:

int child_pid = -1;
atexit(MainCleanupProcess);
...
child_pid = fork();
if (child_pid==0)
{
  atexit(CleanupChildProcess);
  ...

Quote:}

void MainCleanupProcess(void)
{
  if (child_pid != 0)
  {
    /* destroy semaphores */
  }

Quote:}

Thanks in advance,
Chris.

: Hello all,

: Consider the following situation:

: A parent process allocates a set of semaphores. It then begins to
: spawn children (which use the semaphores). The semaphores are
: a global resource and so need to be explicitly destroyed; however
: if a *child* process destroys them accidentally then things could
: get *. So the question becomes: where is the best place to
: clean up?

Why don't you just destroy them in the parent after you have waited for
the children?

G.

In other words: my "wait for the children to terminate" code (and all of
the other cleanup clauses with it) automatically becomes part of any
child process's cleanup too, unless I use some hack that probably
involves a race condition.

Chris.

 Chris> [...] I was asking for the official/ orthodox method (as
 Chris> compared to what I posted) for separating the parent's cleanup
 Chris> from a child's cleanup, since fork()-ing makes a child inherit
 Chris> the same signal handlers and exit procedures as the parent.

Personally I've done this by checking in the cleanup code that
getpid() == creator_pid. I'm not aware of any more 'orthodox' method.

--

"Ceterum censeo Microsoftam delendam esse" - Alain Knaff in nanam