Refactor/fix arenas manipulation.

Abstract arenas access to use arena_get() (or a0get() where appropriate)
rather than directly reading e.g. arenas[ind].  Prior to the addition of
the arenas.extend mallctl, the worst possible outcome of directly
accessing arenas was a stale read, but arenas.extend may allocate and
assign a new array to arenas.

Add a tsd-based arenas_cache, which amortizes arenas reads.  This
introduces some subtle bootstrapping issues, with tsd_boot() now being
split into tsd_boot[01]() to support tsd wrapper allocation
bootstrapping, as well as an arenas_cache_bypass tsd variable which
dynamically terminates allocation of arenas_cache itself.

Promote a0malloc(), a0calloc(), and a0free() to be generally useful for
internal allocation, and use them in several places (more may be
appropriate).

Abstract arena->nthreads management and fix a missing decrement during
thread destruction (recent tsd refactoring left arenas_cleanup()
unused).

Change arena_choose() to propagate OOM, and handle OOM in all callers.
This is important for providing consistent allocation behavior when the
MALLOCX_ARENA() flag is being used.  Prior to this fix, it was possible
for an OOM to result in allocation silently allocating from a different
arena than the one specified.

include/jemalloc/internal/private_symbols.txt

@@ -1,11 +1,16 @@
 a0calloc
 a0free
+a0get
 a0malloc
+arena_get
+arena_get_hard
 arena_alloc_junk_small
 arena_bin_index
 arena_bin_info
 arena_bitselm_get
 arena_boot
+arena_choose
+arena_choose_hard
 arena_chunk_alloc_huge
 arena_chunk_dalloc_huge
 arena_cleanup
@@ -19,6 +24,7 @@ arena_dalloc_large_locked
 arena_dalloc_small
 arena_dss_prec_get
 arena_dss_prec_set
+arena_init
 arena_malloc
 arena_malloc_large
 arena_malloc_small
@@ -42,9 +48,11 @@ arena_mapbitsp_read
 arena_mapbitsp_write
 arena_maxclass
 arena_maxrun
+arena_migrate
 arena_miscelm_get
 arena_miscelm_to_pageind
 arena_miscelm_to_rpages
+arena_nbound
 arena_new
 arena_palloc
 arena_postfork_child
@@ -69,10 +77,8 @@ arena_salloc
 arena_sdalloc
 arena_stats_merge
 arena_tcache_fill_small
-arenas
-arenas_cleanup
-arenas_extend
-arenas_lock
+arenas_cache_bypass_cleanup
+arenas_cache_cleanup
 atomic_add_u
 atomic_add_uint32
 atomic_add_uint64
@@ -100,8 +106,6 @@ bitmap_size
 bitmap_unset
 bt_init
 buferror
-choose_arena
-choose_arena_hard
 chunk_alloc_arena
 chunk_alloc_base
 chunk_alloc_default
@@ -247,7 +251,8 @@ malloc_mutex_unlock
 malloc_printf
 malloc_snprintf
 malloc_strtoumax
-malloc_tsd_boot
+malloc_tsd_boot0
+malloc_tsd_boot1
 malloc_tsd_cleanup_register
 malloc_tsd_dalloc
 malloc_tsd_malloc
@@ -259,8 +264,7 @@ map_bias
 map_misc_offset
 mb_write
 mutex_boot
-narenas_auto
-narenas_total
+narenas_cache_cleanup
 narenas_total_get
 ncpus
 nhbins
@@ -363,6 +367,7 @@ tcache_alloc_small
 tcache_alloc_small_hard
 tcache_arena_associate
 tcache_arena_dissociate
+tcache_arena_reassociate
 tcache_bin_flush_large
 tcache_bin_flush_small
 tcache_bin_info
@@ -388,11 +393,14 @@ tsd_booted
 tsd_arena_get
 tsd_arena_set
 tsd_boot
+tsd_boot0
+tsd_boot1
 tsd_cleanup
 tsd_cleanup_wrapper
 tsd_fetch
 tsd_get
-tsd_get_wrapper
+tsd_wrapper_get
+tsd_wrapper_set
 tsd_initialized
 tsd_init_check_recursion
 tsd_init_finish