Compiler issues - (Josh, please?)
We have a medium-sized project that has begun encountering occasional/rare
(but at least daily during normal workloads) compilation issues that appear
to be related to name/type resolution. There can be code within a method
output where the name resolves correctly to its type in one part of the
method's js output and elsewhere within the same js method output as if it
was Object/untyped. This is most obvious with XML or XMLList instances
(because of .child('prop') vs ['prop] differences). I've also seen it get
confused between local variables and instance properties in some cases,
which I believe is a manifestation of the same thing. In other words,
different compilation runs with the exact same settings are not
completely deterministic, because sometimes they can provide different
output. It is very difficult to repro, because it feels so random. But it
has been something that appears to be more frequent as the codebase grows
(when all other settings remain the same). This led me to consider that it
could be GC-related, and I recently removed the SoftReferences inside
ASScopeCache, as a prime suspect.
After doing this, I have not seen the problem since (so far - after 1.5
days)
The ASScopeCache instances themselves are weakly held (inside
CompilerProject). So the internal maps inside each of these instances being
weakly held as well seems to be the problem, the internal maps can perhaps
get into a partially cleared state between threads.
I did some memory profiling with and without this change for removing the
SoftReferences inside ASScopeCache - but it was quite limited (just testing
with compiling the one project). The memory usage was not much different on
a typical run (approx 1Mb difference for a compilation with around 1000 .as
and .mxml files combined, alongside a bunch of local swcs). There was
possibly a small speed up without the SoftReferences, but I did not test
enough to be sure.
But so far it seems there is not a big impact on memory with omitting
these. If it introduces consistency I'm kinda keen to get it in there - I
know others have definitely seen this problem too.
And for Josh in particular: I think your compiler experience dwarfs the
rest of us and wanted to get your feedback instead of just jumping in with
this one. One option could also be to make this change as a compiler
option, with the new non-weak references being the default, but with the
ability to switch to the older behaviour via the option if that was
considered important as well... look forward to hearing your thoughts.
