[PATCH 3/3] Refactor atfork handlers

[Florian Weimer]

On 02/08/2018 01:50 PM, Adhemerval Zanella wrote:
> +static struct fork_handler *
> +fork_handler_list_find_if (struct fork_handler_list *fork_handlers,
> +			   void *dso_handle)

Should be called _find, not find_if (no callback is involved).

> +  struct fork_handler *first = fork_handler_list_find_if (&fork_handlers,
> +							  dso_handle);
> +  /* Removing is done by shifting the elements in the way the elements
> +     that are not to be removed appear in the beginning in dynarray.
> +     This avoid the quadradic run-time if a naive strategy to remove and
> +     shift one element at time.  */
> +  if (first != NULL)
> +    {
> +      struct fork_handler *result = first;

result should probably be called new_end or something like that.

> +      first++;
> +      for (; first != fork_handler_list_end (&fork_handlers); ++first)
> +	{
> +	  if (first->dso_handle != dso_handle)
> +	    {
> +	      memcpy (result, first, sizeof (struct fork_handler));

Wouldn't a simple struct assignment work here?

I think this patch is a step in the right direction, so it should go in 
with these changes.

However, I think we should make a few improvements in follow-up fixes:

Reduce RSS usage for the common case that no atfork handlers are ever 
registered.  This will be the case once we remove the bogus 
__reclaim_stacks function.

Make a temporary copy of the handler array during fork.  This has two 
benefits: We can run the handlers without acquiring the handler lock (to 
avoid application deadlocks).  We also make sure that a handler does not 
run in a child process which did not run in the parent process.  I think 
the old implementation had both properties.

Thanks,
Florian