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.

1 files changed, 13 insertions, 1 deletions

diff --git a/src/tcache.c b/src/tcache.c
index 2c968c6..1bf7026 100644
--- a/src/tcache.c
+++ b/src/tcache.c
@@ -246,6 +246,14 @@ tcache_arena_associate(tcache_t *tcache, arena_t *arena)
 }
 
 void
+tcache_arena_reassociate(tcache_t *tcache, arena_t *arena)
+{
+
+	tcache_arena_dissociate(tcache);
+	tcache_arena_associate(tcache, arena);
+}
+
+void
 tcache_arena_dissociate(tcache_t *tcache)
 {
 
@@ -261,13 +269,17 @@ tcache_arena_dissociate(tcache_t *tcache)
 tcache_t *
 tcache_get_hard(tsd_t *tsd)
 {
+	arena_t *arena;
 
 	if (!tcache_enabled_get()) {
 		if (tsd_nominal(tsd))
 			tcache_enabled_set(false); /* Memoize. */
 		return (NULL);
 	}
-	return (tcache_create(choose_arena(tsd, NULL)));
+	arena = arena_choose(tsd, NULL);
+	if (unlikely(arena == NULL))
+		return (NULL);
+	return (tcache_create(arena));
 }
 
 tcache_t *