Driver question

Sean Hinde Sean.Hinde@REDACTED
Tue Aug 28 21:05:38 CEST 2001


I just found that it apears to be related to the fact that I was calling the
routine from the shell. I guess the shell was holding onto results of old
function calls or some such thing. If I call this in another process it
works beautifully - even in a tight loop the binaries are cleared to refc 1
after 4 or 5 more calls.

Cheers,
Sean

> 
> Hi,
> 
> A further question about the suggestion below:
> 
> > Yes they do. They might be exactly what you need. The 
> driver binaries
> > are reference counted, and when you call driver_allocate_binary(),
> > refcnt is set to 1 (only the driver is holding the binary).
> > 
> > When you later call driver_output_binary(), refcnt is 
> > incremented to 2,
> > and note that the driver must not change the contents from 
> > now on, since
> > erlang processes now can see the data and depend on this. The driver
> > migth as well call driver_free_binary(), which just 
> decrements refcnt.
> > Only when refcnt decrements to 0, the binary is actually freed.
> > 
> > Every erlang process that now receives the binary will 
> > increment refcnt,
> > and when the binary is garbage collected and found to be 
> unused refcnt
> > is decremented and finaly freed by the last erlang processe 
> > that garbage
> > collects it.
> 
> I have played with this somewhat.. I allocate the binary in 
> the driver and send the result to erlang. The refc is now 2 
> (although it sometime goes to 3 for a short time?). I do not 
> free it at this time as I want to read the refc in a future 
> call to my driver and then if it is back to 1 I can free up a 
> whole load of other stuff as well as the binary.
> 
> I have a fixed size array of handles so it is possible for 
> them all to be used up in which case I return "congestion".
> 
> The behaviour I can't quite figure out though is that of 
> erlang:garbage_collect(). If I call this, the binaries are 
> not immediately reduced to refc = 1. It takes something like 
> 10 seconds before any of them are freed and then some appear 
> to never be freed.
> 
> My binaries are 2 octets long.
> 
> Any thoughts on the behaviour of the garbage collector in 
> this situation?
> 
> Thanks,
> Sean
> 



NOTICE AND DISCLAIMER:
This email (including attachments) is confidential.  If you have received
this email in error please notify the sender immediately and delete this
email from your system without copying or disseminating it or placing any
reliance upon its contents.  We cannot accept liability for any breaches of
confidence arising through use of email.  Any opinions expressed in this
email (including attachments) are those of the author and do not necessarily
reflect our opinions.  We will not accept responsibility for any commitments
made by our employees outside the scope of our business.  We do not warrant
the accuracy or completeness of such information.




More information about the erlang-questions mailing list