Fix arena_run_alloc_large_helper() to not convert size to usize when
searching for the first best fit via arena_run_first_best_fit().  This
allows the search to consider the optimal quantized size class, so that
e.g. allocating and deallocating 40 KiB in a tight loop can reuse the
same memory.

This regression was nominally caused by
5707d6f9 (Quantize szad trees by size
class.), but it did not commonly cause problems until
8a03cf03 (Implement cache index
randomization for large allocations.).  These regressions were first
released in 4.0.0.

This resolves #487.

Fix chunk_alloc_cache() to support decommitted allocation, and use this
ability in arena_chunk_alloc_internal() and arena_stash_dirty(), so that
chunks don't get permanently stuck in a hybrid state.

This resolves #487.

This resolves #485.

OS X 10.12 deprecated OSSpinLock; os_unfair_lock is the recommended
replacement.

Fix zone_force_unlock() to reinitialize, rather than unlocking mutexes,
since OS X 10.12 cannot tolerate a child unlocking mutexes that were
locked by its parent.

Refactor; this was a side effect of experimenting with zone
{de,re}registration during fork(2).

_exit(2) is async-signal-safe, whereas exit(3) is not.

Monitoring thread creation is unimplemented for Windows, which means
lazy-lock cannot function correctly.

This resolves #310.

This resolves #474.

This resolves #396.

The raw clock variant is slow (even relative to plain CLOCK_MONOTONIC),
whereas the coarse clock variant is faster than CLOCK_MONOTONIC, but
still has resolution (~1ms) that is adequate for our purposes.

This resolves #479.

Some applications wrap various system calls, and if they call the
allocator in their wrappers, unexpected reentry can result.  This is not
a general solution (many other syscalls are spread throughout the code),
but this resolves a bootstrapping issue that is apparently common.

This resolves #443.

This works around malloc_conf not being properly initialized by at least
the cygwin toolchain.  Prior build system changes to use
-Wl,--[no-]whole-archive may be necessary for malloc_conf resolution to
work properly as a non-weak symbol (not tested).

This is generally correct (no need for weak symbols since no jemalloc
library is involved in the link phase), and avoids linking problems
(apparently unininitialized non-NULL malloc_conf) when using cygwin with
gcc.

glibc defines its malloc implementation with several weak and strong
symbols:

strong_alias (__libc_calloc, __calloc) weak_alias (__libc_calloc, calloc)
strong_alias (__libc_free, __cfree) weak_alias (__libc_free, cfree)
strong_alias (__libc_free, __free) strong_alias (__libc_free, free)
strong_alias (__libc_malloc, __malloc) strong_alias (__libc_malloc, malloc)

The issue is not with the weak symbols, but that other parts of glibc
depend on __libc_malloc explicitly.  Defining them in terms of jemalloc
API's allows the linker to drop glibc's malloc.o completely from the link,
and static linking no longer results in symbol collisions.

Another wrinkle: jemalloc during initialization calls sysconf to
get the number of CPU's.  GLIBC allocates for the first time before
setting up isspace (and other related) tables, which are used by
sysconf.  Instead, use the pthread API to get the number of
CPUs with GLIBC, which seems to work.

This resolves #442.

This is intended to drop memory usage to a level that AppVeyor test
instances can handle.

This resolves #393.

This resolves #393.

This resolves #393.

This fixes warnings when building with MSVC.

Conditionalize use of --whole-archive on the platform plus compiler,
rather than on the ABI.  This fixes a regression caused by
7b24c6e5 (Use --whole-archive when
linking integration tests on MinGW.).

This reverts 13473c7c, which was
intended to work around bootstrapping issues when linking statically.
However, this actually causes problems in various other configurations,
so this reversion may force a future fix for the underlying problem, if
it still exists.

Use the correct level metadata when allocating child nodes so that leaf
nodes don't end up over-sized (2^16 elements vs 2^4 elements).

Prior to this change, the malloc_conf weak symbol provided by the
jemalloc dynamic library is always used, even if the application
provides a malloc_conf symbol.  Use the --whole-archive linker option
to allow the weak symbol to be overridden.

Refactor tsd so that tsdn_fetch() does not trigger allocation, since
allocation could cause infinite recursion.

This resolves #458.

Rather than protecting dss operations with a mutex, use atomic
operations.  This has negligible impact on synchronization overhead
during typical dss allocation, but is a substantial improvement for
chunk_in_dss() and the newly added chunk_dss_mergeable(), which can be
called multiple times during chunk deallocations.

This change also has the advantage of avoiding tsd in deallocation paths
associated with purging, which resolves potential deadlocks during
thread exit due to attempted tsd resurrection.

This resolves #425.

Add spin_t and spin_{init,adaptive}(), which provide a simple
abstraction for adaptive spinning.

Adaptively spin during busy waits in bootstrapping and rtree node
initialization.

Explicitly disallow junk:true and junk:free runtime settings when
running in Valgrind, since deallocation-time junk filling and redzone
validation cause false positive Valgrind reports.

This resolves #470.

Simplify decay-based purging attempts to only be triggered when the
epoch is advanced, rather than every time purgeable memory increases.
In a correctly functioning system (not previously the case; see below),
this only causes a behavior difference if during subsequent purge
attempts the least recently used (LRU) purgeable memory extent is
initially too large to be purged, but that memory is reused between
attempts and one or more of the next LRU purgeable memory extents are
small enough to be purged.  In practice this is an arbitrary behavior
change that is within the set of acceptable behaviors.

As for the purging fix, assure that arena->decay.ndirty is recorded
*after* the epoch advance and associated purging occurs.  Prior to this
fix, it was possible for purging during epoch advance to cause a
substantially underrepresentative (arena->ndirty - arena->decay.ndirty),
i.e. the number of dirty pages attributed to the current epoch was too
low, and a series of unintended purges could result.  This fix is also
relevant in the context of the simplification described above, but the
bug's impact would be limited to over-purging at epoch advances.

Instead, move the epoch backward in time.  Additionally, add
nstime_monotonic() and use it in debug builds to assert that time only
goes backward if nstime_update() is using a non-monotonic time source.

Add missing #include <time.h>.  The critical time facilities appear to
have been transitively included via unistd.h and sys/time.h, but in
principle this omission was capable of having caused
clock_gettime(CLOCK_MONOTONIC, ...) to have been overlooked in favor of
gettimeofday(), which in turn could cause spurious non-monotonic time
updates.

Refactor nstime_get() out of nstime_update() and add configure tests for
all variants.

Add CLOCK_MONOTONIC_RAW support (Linux-specific) and
mach_absolute_time() support (OS X-specific).

Do not fall back to clock_gettime(CLOCK_REALTIME, ...).  This was a
fragile Linux-specific workaround, which we're unlikely to use at all
now that clock_gettime(CLOCK_MONOTONIC_RAW, ...) is supported, and if we
have no choice besides non-monotonic clocks, gettimeofday() is only
incrementally worse.