When an exact (non-integer) rational is reconstructed from a place
message, normalization could involve bignum operations --- and those
operations might use a cache, but the cache should not refer to the
pages that are specific to a place message being constructed.
Normalization isn't necessary, since the parts were already in a
rational, so the repair is just it skip it.
Relevant to #3456
A table of subprocess handles to finalize was not place-local as it
should have been. The same was true of a table of resolved IP
addresses to finalize.
Related to #3456
The Racket variant of Chez Scheme includes special treatment of deeply
nested structures to avoid a C-stack overflow on unfasl, but the
relevant callbacks had gotten mangled.
Closes#3454
When a would-be loop is called in a would-be loop that turns out not
to be a loop due to an intervening non-loop layer, the outer would-be
loop was not detected as a non-loop.
When the mutability decision on a variable is delayed, but then the
variable is discovered to be mutable before the delay is triggered,
then mutability information could get lost.
Mutability analysis may determine that a `set!` is dead code, and then
the mutated variable might be optimized away, so don't leave the dead
`set!` behind.
When the srcloc-enriched S-expression representation a function that
is available for cross-module inlining has a source that is not a
path, string, or symbol, then the source has to be dropped in the
module's serialized form.
On a 64-bit machine, the problem was a `<` versus `<=`.
On a 32-bit machine where 4294967087 is not a fixnum, the
problem was in how bignums are handled.
Previously, `error` would raise an `exn:fail` with the following message,
because it treated the first of the three strings as a format string
and the other two as its arguments:
> error: format string requires 0 arguments, given 2;
> arguments were:
> " is a procedure, to always escape when called"
> " (by calling raise-blame-error with the arguments it was given"`
The main change is to disable forced GCs during the documentation
phase in a parallel `raco setup`. Since each GC is global (instead of
place local) in Racket CS, these forced GCs created a scaling problem.
Furthermore, they're not really necessary; peak memory use tends to
remain the same without them in a parallel build, since the
".zo"-building phase doens't have extra collections and tends to
establish peak memory use.
A non-parallel build still includes explicitly forced GCs. In that
mode, the cost is modest while reducing peak use by 30%.
A new environment variable appends timestamps (in process time since
startup) for each status line, which is useful for generating more
detailed build plots.
Since a GC with accounting doesn't run in parallel, it discards
owner-thread information (ironically) that is used for parallel
collection. Losing ownership information could reduce parallelism in
later collections --- but only if they run without accounting.
This commit does not turn on ownership tracking, however, because
experiments suggest that it isn't worthwhile for Racket:
* Preserving ownership information slows down a major collection in
accounting mode by 5-10%.
* Racket uses accounting mode only for full collections, and the loss
of ownership information would mostly affect only later full
collections. Since accounting momde tends to stick around, very
little parallelism is actually lost.
* Without further work, accounting mode cannot benefit from
parallelization, because it works by stepping sequentially through
accounting domains, and that aligns with thread ownership. A
possible improvement is to look ahead in the accounting-domain
object sequence to find one that starts in another ownership
domain, and then constrain concurrent tracing from that object to
keep the count private and not leave the ownership domain until the
accounting sequence has caught up.
Besides making it easier to turn on "parallel" collection for
accounting mode, the small refactorings here make it easier to bring
more things, like guardian and weak-pair handling, into the parallel
part of a collection. So, the changes are probably worth keeping for
that purpose.
At some point in September 2020, q.com:9887 stopped working for
this test. It's disabled until we can find a replacement.
As far as I can tell, there aren't any sites that behave the way
q.com did prior to September 2020.
The collector tries to use roughly the same amount of parallelism as
the number of active threads, but make sure that it doesn't fall back
to an ownership-mangling non-parallel collection if all but one place
happens to be stalled.
Make the exchange of objects by parallel sweepers --- which is needed
when an object being swept by one thread refers to an object owner by
another thread --- much simpler and slightly faster.
The original design of exchanging memory regions didn't really work
out, and it had degrenerated to essentially exchanging objects.
Explicitly exchanging objects instead of regions makes the GC simpler,
because received objects can be just added to the regular sweep stack,
and less additional space<->type correspondence is needed.
Fix mishandling of an expanded `if` where the test position is a
syntax object. The expander's compiler pass from expanded objects to
linkets knows that the syntax object isn't useful, but it tried to be
helpful by preserving the syntax object's content as quoted --- and
that content turns out not to be available, so the syntax object was
replaced by #f, instead.
Closes#3436
