diff options
Diffstat (limited to 'malloc')
| -rw-r--r-- | malloc/arena.c | 41 |
1 files changed, 36 insertions, 5 deletions
diff --git a/malloc/arena.c b/malloc/arena.c index 229783f3b7..4e16593d8b 100644 --- a/malloc/arena.c +++ b/malloc/arena.c @@ -702,8 +702,7 @@ _int_new_arena (size_t size) } -/* Remove an arena from free_list. The arena may be in use because it - was attached concurrently to a thread by reused_arena below. */ +/* Remove an arena from free_list. */ static mstate get_free_list (void) { @@ -718,7 +717,8 @@ get_free_list (void) free_list = result->next_free; /* The arena will be attached to this thread. */ - ++result->attached_threads; + assert (result->attached_threads == 0); + result->attached_threads = 1; detach_arena (replaced_arena); } @@ -735,6 +735,26 @@ get_free_list (void) return result; } +/* Remove the arena from the free list (if it is present). + free_list_lock must have been acquired by the caller. */ +static void +remove_from_free_list (mstate arena) +{ + mstate *previous = &free_list; + for (mstate p = free_list; p != NULL; p = p->next_free) + { + assert (p->attached_threads == 0); + if (p == arena) + { + /* Remove the requested arena from the list. */ + *previous = p->next_free; + break; + } + else + previous = &p->next_free; + } +} + /* Lock and return an arena that can be reused for memory allocation. Avoid AVOID_ARENA as we have already failed to allocate memory in it and it is currently locked. */ @@ -782,14 +802,25 @@ reused_arena (mstate avoid_arena) (void) mutex_lock (&result->mutex); out: - /* Attach the arena to the current thread. Note that we may have - selected an arena which was on free_list. */ + /* Attach the arena to the current thread. */ { /* Update the arena thread attachment counters. */ mstate replaced_arena = thread_arena; (void) mutex_lock (&free_list_lock); detach_arena (replaced_arena); + + /* We may have picked up an arena on the free list. We need to + preserve the invariant that no arena on the free list has a + positive attached_threads counter (otherwise, + arena_thread_freeres cannot use the counter to determine if the + arena needs to be put on the free list). We unconditionally + remove the selected arena from the free list. The caller of + reused_arena checked the free list and observed it to be empty, + so the list is very short. */ + remove_from_free_list (result); + ++result->attached_threads; + (void) mutex_unlock (&free_list_lock); } |