Aaron Bannert <[EMAIL PROTECTED]> writes:
> Even in the case where APR_PROCESS_LOCK_IS_GLOBAL is _not_ #defined,
> and the lock was created with type APR_LOCKALL, (if I'm reading this
> correctly) acquire() will do:
>
> apr_unix_lock_intra(lock)
> apr_unix_lock_inter(lock)
>
> and release() will do:
>
> apr_unix_unlock_intra(lock)
> apr_unix_unlock_inter(lock)
What this means is that to block out *all* other processes and
threads, unless we're on a system where APR_PROCESS_LOCK_IS_GLOBAL is
defined, we need to get an interprocess lock (to block out everything
but threads in our own process) as well as a intraprocess lock (to
block out other threads in our own process).
> To me it seems that the intraprocess lock would merely serve as a
> bottleneck (for better or worse) for local-process locks, while the
> interprocess lock would be the only lock protecting the central
> resource.
No... See my description above of what the interprocess lock does and
what the intraprocess lock does.
>
> This is compoundedly so when you consider our primary example, where two
> multithreaded processes will compete for the acquire() lock. They can each
> simultaneously acquire the intraprocess lock in their own memory-space,
> but will sill have to compete for the interprocess lock.
If we use a kernel mechanism for interprocess locking which doesn't
block out other threads in the same process then this certainly can
happen.
Generally, APR does use such a kernel mechanism on Unix.
> I also do not see LOCK_ALL used for lock implementation anywhere except
> in the apr/locks/unix/lock.c code. (There is once case in the win32 code,
> but it appears to treat LOCK_ALL and CROSS_PROCESS the same), so the
> who thing seems to hinge on APR_PROCESS_LOCK_IS_GLOBAL. (I could be
> wrong here :)
That simply means that on other platforms and interprocess lock blocks
out other threads in the same process (or that the APR code for those
platforms has a bug :) ).
--
Jeff Trawick | [EMAIL PROTECTED] | PGP public key at web site:
http://www.geocities.com/SiliconValley/Park/9289/
Born in Roswell... married an alien...
