Depending on virtual memory resource limits, it is necessary to attempt
allocating three maximally sized objects to trigger OOM rather than just
two, since the maximum supported size is slightly less than half the
total virtual memory address space.

This fixes a test failure that was introduced by
0c516a00 (Make *allocx() size class
overflow behavior defined.).

This resolves #379.

This assures that side effects of internal allocation don't impact
tests.

This regression was caused by 8f683b94
(Make opt_narenas unsigned rather than size_t.).

Fix bitmap_sfu() to shift by LG_BITMAP_GROUP_NBITS rather than
hard-coded 6 when using linear (non-USE_TREE) bitmap search.  In
practice this affects only 64-bit systems for which sizeof(long) is not
8 (i.e. Windows), since USE_TREE is defined for 32-bit systems.

This regression was caused by b8823ab0
(Use linear scan for small bitmaps).

This resolves #368.

Move chunk_dalloc_arena()'s implementation into chunk_dalloc_wrapper(),
so that if the dalloc hook fails, proper decommit/purge/retain cascading
occurs.  This fixes three potential chunk leaks on OOM paths, one during
dss-based chunk allocation, one during chunk header commit (currently
relevant only on Windows), and one during rtree write (e.g. if rtree
node allocation fails).

Merge chunk_purge_arena() into chunk_purge_default() (refactor, no
change to functionality).

Stack corruption happens in x64 bit

This resolves #347.

Prior to 767d8506 (Refactor arenas array
(fixes deadlock).), it was possible under some circumstances for
arena_get() to trigger recreation of the arenas cache during tsd
cleanup, and the arenas cache would then be leaked.  In principle a
similar issue could still occur as a side effect of decay-based purging,
which calls arena_tdata_get().  Fix arenas_tdata_cleanup() by setting
tsd->arenas_tdata_bypass to true, so that arena_tdata_get() will
gracefully fail (an expected behavior) rather than recreating
tsd->arena_tdata.

Reported by Christopher Ferris <cferris@google.com>.

Add missing stats.arenas.<i>.{dss,lg_dirty_mult,decay_time}
initialization.

Fix stats.arenas.<i>.{pactive,pdirty} to read under the protection of
the arena mutex.

Fix stats.cactive accounting to always increase/decrease by multiples of
the chunk size, even for huge size classes that are not multiples of the
chunk size, e.g. {2.5, 3, 3.5, 5, 7} MiB with 2 MiB chunk size.  This
regression was introduced by 155bfa7d
(Normalize size classes.) and first released in 4.0.0.

This resolves #336.

This removes an implicit conversion from size_t to ssize_t.  For cactive
decreases, the size_t value was intentionally underflowed to generate
"negative" values (actually positive values above the positive range of
ssize_t), and the conversion to ssize_t was undefined according to C
language semantics.

This regression was perpetuated by
1522937e (Fix the cactive statistic.)
and first release in 4.0.0, which in retrospect only fixed one of two
problems introduced by aa5113b1
(Refactor overly large/complex functions) and first released in 3.5.0.

Remove invalid tests that were intended to be tests of (hugemax+1) OOM,
for which tests already exist.

This fixes chunk allocation to reuse retained memory even if an
application-provided chunk allocation function is in use.

This resolves #307.

For small bitmaps, a linear scan of the bitmap is slightly faster than
a tree search - bitmap_t is more compact, and there are fewer writes
since we don't have to propogate state transitions up the tree.
On x86_64 with the current settings, I'm seeing ~.5%-1% CPU improvement
in production canaries with this change.

The old tree code is left since 32bit sizes are much larger (and ffsl
smaller), and maybe the run sizes will change in the future.

This resolves #339.

This resolves #341.

Add HUGE_MAXCLASS overflow checks that are specific to heap profiling
code paths.  This fixes test failures that were introduced by
0c516a00 (Make *allocx() size class
overflow behavior defined.).

This fixes compilation warnings regarding integer overflow that were
introduced by 0c516a00 (Make *allocx()
size class overflow behavior defined.).

Limit supported size and alignment to HUGE_MAXCLASS, which in turn is
now limited to be less than PTRDIFF_MAX.

This resolves #278 and #295.

Refactor the arenas array, which contains pointers to all extant arenas,
such that it starts out as a sparse array of maximum size, and use
double-checked atomics-based reads as the basis for fast and simple
arena_get().  Additionally, reduce arenas_lock's role such that it only
protects against arena initalization races.  These changes remove the
possibility for arena lookups to trigger locking, which resolves at
least one known (fork-related) deadlock.

This resolves #315.

Fix arena_size arena_new() computation to incorporate
runs_avail_nclasses elements for runs_avail, rather than
(runs_avail_nclasses - 1) elements.  Since offsetof(arena_t, runs_avail)
is used rather than sizeof(arena_t) for the first term of the
computation, all of the runs_avail elements must be added into the
second term.

This bug was introduced (by Jason Evans) while merging pull request #330
as 3417a304 (Separate arena_avail
trees).

Merge of 3417a304 looks like a small
bug: first_best_fit doesn't scan through all the classes, since ind is
offset from runs_avail_nclasses by run_avail_bias.