[Mono-dev] Image mempool grows with use of mono_runtime_invoke on value types

[Ewen Cheslack-Postava]

Hi all,

I'm embedding mono in my application.  We happen to call methods from
unmanaged code on value types pretty regularly and we noticed memory
usage getting out of hand after a few days running continuously.  I've
tracked the problem down to the image's mempool which is growing
continuously.  The offending function is
mono_marshal_get_runtime_invoke, specifically the call to
signature_dup_add_this around line 4707 of marshal.c.   The
MonoMethodSignature is duplicated and the memory is allocated from the
image's memory pool.  The cache lookup that is happening after that is
succeeding and the allocated signature just sits around until the
program ends.

So I've tracked the problem down but I'm not sure what to do about it.
 This condition seems to be true for any non-static method invocations
on value types.  Is there some way to get a MonoMethod* which doesn't
have hasthis set so I can avoid this case?  Even if not, is the memory
pool the right place to allocate this from?  It isn't cleaned up until
the image is closed but the signature is immediately discarded.  Even
if I call the same method over and over, a new signature is generated
each time even though it appears they should be identical.  Should
there be a cache for these duplicated signatures as well so the
mempool doesn't have potentially unbounded growth?

Thanks,
-Ewen