While jemalloc_stats is not actively doing anything, it can be
cumbersome to not have it count as an operation, because the operation
count shown on jemalloc_stats doesn't match the line number in the input
replay log, and the offset grows as the number of jemalloc_stats
operations grows.
While here, also update a comment about the replay log format.
It adds an uncompressible and noticeable time overhead to replaying
logs, even when one is not interested in measuring RSS. This has caused
me to clear the method body on multiple occasions.
If necessary, it is possible to enable zero or junk at the allocator
level for the same effect.
SRWLock is more lightweight than CriticalSection, but is only available
on Windows Vista and more. So until we actually dropped support Windows
XP, we had to use CriticalSection.
Now that all supported Windows versions do have SRWLock, this is a
switch we can make, and not only because SRWLock is more lightweight,
but because it can be statically initialized like on other platforms,
allowing to use the same initialization code as on other platforms,
and removing the requirement for a DllMain, which in turn can allow
to statically link mozjemalloc in some cases, instead of requiring a
shared library (DllMain only works on shared libraries), or manually
call the initialization function soon enough.
There is a downside, though: SRWLock, as opposed to CriticalSection, is
not fair, meaning it can have thread scheduling implications, and can
theoretically increase latency on some threads. However, it is the
default used by Rust Mutex, meaning it's at least good enough there.
Let's see how things go with this.
Those macros are one more thing that needs to be added when the
mozjemalloc API surface is increased, but after bug 1399350, nothing
actually needs them, so remove them.
