Phil,
I've now looked into this and hopefully fixed it in CVS.
saveState gets a new segment of memory from the system each time it is
called and copies everything that is reachable from the root into that.
As well being written out the segment needs to be retained as a whole
since if a child state is created the child relies on all the contents
of the parent being at a fixed location. If saveState is called more
than once a new segment is created and most, if not all, of the existing
segment is copied into it. It is possible, though, that some data may
not be copied over because it is only reachable from the stacks of
running threads. Rather than delete existing segments they are turned
into "local" heap segments. These local segments are managed by the
normal garbage collector and the GC may deallocate and return them to
the system pool if they are no longer required. The solution to these
"Out of Memory" exceptions is simply to call FullGC between calls to
saveState and that's what I've done. The segfault was as a result of
not handling cleanly the case of being unable to allocate a new segment
part-way through the state saving, and I've fixed that.
Let me know if there are still problems.
Regards,
David
Philip Clayton wrote:
David,
We have noticed some interesting behaviour with the state saving in
Poly/ML 5.2/5.2.1--- possibly a sign that something isn't quite as
intended.
If poly is started and the command
PolyML.SaveState.saveState "test";
is repeatedly entered, a segmentation fault eventually occurs. On my
machine it always happens after 22 times. With the debug level set to 2
or 3, we get:
Bad pointer 0x0d479050 found
Aborted
If we enter
PolyML.fullGC ();
just before the 22nd go, there is no segmentation fault. However,
continuing to enter the original save state command results in the
exception
Exception- SysErr ("Out of Memory", SOME ENOMEM) raised
after 8 more goes.
We found this example more by chance. We have had a few other
repeatable segmentation faults when saving the state but on very large
examples and these are hard to reduce down. (They may be related to the
above issue.) In each case, the segmentation fault could be avoided by
executing PolyML.fullGC first. Generally, if we cannot create an SML
script that generates an error, what is the best way to track down an
issue?
Thanks,
Phil
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