Re: (forks) When do I need to lock variables?

At 13:52 +0200 9/23/03, Per Andreas Buer wrote:
>I've playing around with forks and forks::shared for some time now - it
>looks really nifty. In the past I've been spending too much time
>emulating threads in Perl. :/
>I am not quite sure when I need to lock. Is "$HASH{foo}++" safe?

In general, increment on a shared variable is not safe.  It's safe in 
the sense that Perl won't crash.  It's _not_ save in the sense that 
you might miss increments.  This is because shared variables in Perl 
are implemented as tied variables, i.e. with a FETCH and STORE.  An 
increment is this basically a FETCH, an increment and a STORE.  If 
second thread does a FETCH before the first one has done the STORE, 
you have lost 1 increment.


>  How
>about "$foo = scalar keys %HASH"? Should a wrap access to shared lists
>and hashed with tie and lock there?

I'm not sure what you mean here...


Liz