1. The current asynchronous behavior is pointless, because we still remove the
hashtable entry synchronously, which deletes the value, and it's the value
we're using.
2. Trying to asynchronously delete the value is difficult, and not currently
needed because we can't get a memory-pressure notification while we're using
the value, and hence can't expire it from the expiration tracker.
Note: we can't get this memory-pressure notification because the stage 2 of
mozalloc_handle_oom() to reclaim memory when OOM is not implemented yet.
In order to avoid the possibility of a deadlock if the DMD state lock is
currently acquired when forking a |pthread_atfork| hook is added to wait for
and acquire the lock prior to forking, then release it after forking.
Adapted from
4e2e3dd9cf
and
d9f7b2a430
As per the latter commit, it would seem unlocking, in fork() child
processes, mutexes that were locked in the parent process is not really
well supported on OSX 10.12. The addition of the zone_reinit_lock
function in 10.12 supports this idea.
Some system libraries are using malloc_default_zone() and then using
some of the malloc_zone_* API. Under normal conditions, those functions
check the malloc_zone_t/malloc_introspection_t struct for the values
that are allowed to be NULL, so that a NULL deref doesn't happen.
As of OSX 10.12, malloc_default_zone() doesn't return the actual default
zone anymore, but returns a fake, wrapper zone. The wrapper zone defines
all the possible functions in the malloc_zone_t/malloc_introspection_t
struct (almost), and calls the function from the registered default zone
(jemalloc in our case) on its own. Without checking whether the pointers
are NULL.
This means that a system library that calls e.g.
malloc_zone_batch_malloc(malloc_default_zone(), ...) ends up trying to
call jemalloc_zone.batch_malloc, which is NULL, and crash follows.
So as of OSX 10.12, the default zone is required to have all the
functions available (really, the same as the wrapper zone), even if they
do nothing.
This is arguably a bug in libsystem_malloc in OSX 10.12, but jemalloc
still needs to work in that case.
[Adapted from
c6943acb3c]
The SDK jemalloc is built against might be not be the latest for various
reasons, but the resulting binary ought to work on newer versions of
OSX.
In order to ensure this, we need the fullest definitions possible, so
copy what we need from the latest version of malloc/malloc.h available
on opensource.apple.com.
[Adapted from
c68bb41793]
We have been using a different zone allocator between mozjemalloc and
replace-malloc for a long time. Jemalloc 4 uses the same as
replace-malloc, albeit as part of the jemalloc upstream code base.
We've been bitten many times in the past with Apple changes breaking the
zone allocator, and each time we've had to make changes to the three
instances, although two of them are similar and the changes there are
straightforward.
It also turns out that the way the mozjemalloc zone allocator is set up,
when a new version of OSX appears with a new version of the system zone
allocator, Firefox ends up using the system allocator, because the zone
allocator version is not supported.
So, we use the same zone allocator for both replace-malloc and
mozjemalloc, making everything on par with jemalloc 4.
The intent here is to reuse the zone allocator for mozjemalloc, to avoid
all the shortcomings of mozjemalloc using a different one. This change
only moves the replace-malloc zone allocator out of replace-malloc.c, to
make changes for mozjemalloc integration clearer.
Somehow, we never called those hooks when replace-malloc is enabled. I'd
expect this to cause random deadlocks when forking, and I'm surprised
this hasn't surfaced. Maybe it actually causes some intermittent oranges
on automation, who knows.
This also brings consistency with what is done for jemalloc 4, and with
the mozjemalloc implementation, too, that we're going to replace with
this one in a subsequent changeset.
Bug 1300948 added thread-ids to logalloc logs, and logalloc_munge.py was
munging them all as if they were all under the same namespace. But when
filtering munged logs to only contain logs from a given process,
thread-ids then don't necessarily start from 1, which would be the
desired outcome.
So use a different pool of thread-ids for each process.
Bug 1207519 added maybe_pod_* methods to the allocation policy
classes, but did not add them to InfallibleAllocPolicy.
I think the idea of these methods is that the callers are explicitly
opting into fallible behavior, so they will deal with any errors that
occur. For instance, in js::HashTable, this is used to try to shrink
the hash table when there are a lot of unused entries. If the shrink
fails, it just continues to use the existing block of memory.
However, having fallible methods in a supposedly infallible class is
weird, so for now, just use the infallible version.
MozReview-Commit-ID: 97D66Z4oLfl
