Re: PATCH: zselect builtin.

[Peter Stephenson <pws@csr.com>]

Peter Stephenson wrote:
> Warning:  I used this overnight as part of a test and there seems to be
> a memory leak somewhere, not necessarily zselect itself (where I can't
> see where it would be).  I was using ztcp, but it was the same TCP
> connection all the time, so I don't think that's it either.  It's just
> possible I was accumulating some humongous array, but I couldn't see
> where that would have been, either.  Unfortunately I had to kill the
> shell because I made it uninteruptible.
                                /\
                                r

I'm 90% sure I know what's causing this, and it's nothing to do with the
modules.  The memory is released when the code returns to the top level
(at least by the application layer: it doesn't get returned to the
system, but when I restart the function it takes a long while before it
needs more memory from the system, indicating the shell has finished
with the previous allocation).  This indicates something is hogging it
until the return to top-level processing.  There is one obvious candidate.

When a function is executed, it gets copied to a new structure tree.
When this is finished with, it gets passed to freeeprog().  But that
doesn't free it, in case something is still executing it.  It only gets
freed by freeeprogs() when control returns to the top level.  As my
function executes in a while loop, this never happens.  I tested this by
removing all function calls from the while loop and putting the builtins
inline, and the memory stopped increasing.

This is pretty disastrous.  We need a better way of deciding whether to
free Eprog's.  I can't see why we shouldn't use some reference count
mechanism.

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR Ltd., Science Park, Milton Road,
Cambridge, CB4 0WH, UK                          Tel: +44 (0)1223 392070


**********************************************************************
The information transmitted is intended only for the person or
entity to which it is addressed and may contain confidential 
and/or privileged material. 
Any review, retransmission, dissemination or other use of, or
taking of any action in reliance upon, this information by 
persons or entities other than the intended recipient is 
prohibited.  
If you received this in error, please contact the sender and 
delete the material from any computer.
**********************************************************************