[Spread-users] Question about thread-safety

[Theo E. Schlossnagle]

John Schultz wrote:
> On Wed, 18 Jun 2003, Theo E. Schlossnagle wrote:
>>You said that the opaque integer reference is used in libraries.  I'd be
>>interested at looking at a completed product that uses such a method and
>>compare it against other libraries that use a standard context set up (like
>>OpenSSL, Sybase, MySQL, Postgres, etc.)
> 
> 
> I wouldn't use this method in every application/library.  For example,
> there is no reason to hide an in-memory data structure (e.g. - a linked
> list) behind an opaque integer handle.  However, because Spread performs
> system IO and has to protect its file descriptors carefully (the race
> condition that started all of this), the Spread user library is a good
> candidate for this treatment.
> 
> I intend to eventually implement this in a new Spread user library.  At
> that time we can compare the performance of the new library vs. the old
> and see if there is any noticeable overhead.

I think your method will have no noticeable overhead.  That wasn't my concern 
at all.

My concern was handling multithreaded _AND_ multiprocess applications equally 
well.  So, the implementation must keep in mind that there are subtleties with 
fork() duplicating the internal table/hash you use for managing the contexts 
of user sessions.

The implementation needs to have a graceful way of deallocating a session in a 
child process that inherited it without wanting it.

Since we are about 20 minutes apart, maybe we should talk about this in 
person.  [I certainly hope] we can come up with a better solution together 
than either of us alone.

-- 
Theo Schlossnagle
Principal Consultant
OmniTI Computer Consulting, Inc. -- http://www.omniti.com/
Phone:  +1 410 872 4910 x201     Fax:  +1 410 872 4911
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