/* Malloc implementation for multiple threads without lock contention. Copyright (C) 2001-2016 Free Software Foundation, Inc. This file is part of the GNU C Library. Contributed by Wolfram Gloger , 2001. The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. The GNU C Library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with the GNU C Library; see the file COPYING.LIB. If not, see . */ #include /* Compile-time constants. */ #define HEAP_MIN_SIZE (32 * 1024) #ifndef HEAP_MAX_SIZE # ifdef DEFAULT_MMAP_THRESHOLD_MAX # define HEAP_MAX_SIZE (2 * DEFAULT_MMAP_THRESHOLD_MAX) # else # define HEAP_MAX_SIZE (1024 * 1024) /* must be a power of two */ # endif #endif /* HEAP_MIN_SIZE and HEAP_MAX_SIZE limit the size of mmap()ed heaps that are dynamically created for multi-threaded programs. The maximum size must be a power of two, for fast determination of which heap belongs to a chunk. It should be much larger than the mmap threshold, so that requests with a size just below that threshold can be fulfilled without creating too many heaps. */ /***************************************************************************/ #define top(ar_ptr) ((ar_ptr)->top) /* A heap is a single contiguous memory region holding (coalesceable) malloc_chunks. It is allocated with mmap() and always starts at an address aligned to HEAP_MAX_SIZE. */ typedef struct _heap_info { mstate ar_ptr; /* Arena for this heap. */ struct _heap_info *prev; /* Previous heap. */ size_t size; /* Current size in bytes. */ size_t mprotect_size; /* Size in bytes that has been mprotected PROT_READ|PROT_WRITE. */ /* Make sure the following data is properly aligned, particularly that sizeof (heap_info) + 2 * SIZE_SZ is a multiple of MALLOC_ALIGNMENT. */ char pad[-6 * SIZE_SZ & MALLOC_ALIGN_MASK]; } heap_info; /* Get a compile-time error if the heap_info padding is not correct to make alignment work as expected in sYSMALLOc. */ extern int sanity_check_heap_info_alignment[(sizeof (heap_info) + 2 * SIZE_SZ) % MALLOC_ALIGNMENT ? -1 : 1]; /* Thread specific data. */ static __thread mstate thread_arena attribute_tls_model_ie; /* Arena free list. free_list_lock synchronizes access to the free_list variable below, and the next_free and attached_threads members of struct malloc_state objects. No other locks must be acquired after free_list_lock has been acquired. */ static mutex_t free_list_lock = _LIBC_LOCK_INITIALIZER; static size_t narenas = 1; static mstate free_list; /* list_lock prevents concurrent writes to the next member of struct malloc_state objects. Read access to the next member is supposed to synchronize with the atomic_write_barrier and the write to the next member in _int_new_arena. This suffers from data races; see the FIXME comments in _int_new_arena and reused_arena. list_lock also prevents concurrent forks. At the time list_lock is acquired, no arena lock must have been acquired, but it is permitted to acquire arena locks subsequently, while list_lock is acquired. */ static mutex_t list_lock = _LIBC_LOCK_INITIALIZER; /* Mapped memory in non-main arenas (reliable only for NO_THREADS). */ static unsigned long arena_mem; /* Already initialized? */ int __malloc_initialized = -1; /**************************************************************************/ /* arena_get() acquires an arena and locks the corresponding mutex. First, try the one last locked successfully by this thread. (This is the common case and handled with a macro for speed.) Then, loop once over the circularly linked list of arenas. If no arena is readily available, create a new one. In this latter case, `size' is just a hint as to how much memory will be required immediately in the new arena. */ #define arena_get(ptr, size) do { \ ptr = thread_arena; \ arena_lock (ptr, size); \ } while (0) #define arena_lock(ptr, size) do { \ if (ptr && !arena_is_corrupt (ptr)) \ (void) mutex_lock (&ptr->mutex); \ else \ ptr = arena_get2 ((size), NULL); \ } while (0) /* find the heap and corresponding arena for a given ptr */ #define heap_for_ptr(ptr) \ ((heap_info *) ((unsigned long) (ptr) & ~(HEAP_MAX_SIZE - 1))) #define arena_for_chunk(ptr) \ (chunk_non_main_arena (ptr) ? heap_for_ptr (ptr)->ar_ptr : &main_arena) /**************************************************************************/ #ifndef NO_THREADS /* atfork support. */ static void *(*save_malloc_hook)(size_t __size, const void *); static void (*save_free_hook) (void *__ptr, const void *); static void *save_arena; # ifdef ATFORK_MEM ATFORK_MEM; # endif /* Magic value for the thread-specific arena pointer when malloc_atfork() is in use. */ # define ATFORK_ARENA_PTR ((void *) -1) /* The following hooks are used while the `atfork' handling mechanism is active. */ static void * malloc_atfork (size_t sz, const void *caller) { void *victim; if (thread_arena == ATFORK_ARENA_PTR) { /* We are the only thread that may allocate at all. */ if (save_malloc_hook != malloc_check) { return _int_malloc (&main_arena, sz); } else { if (top_check () < 0) return 0; victim = _int_malloc (&main_arena, sz + 1); return mem2mem_check (victim, sz); } } else { /* Suspend the thread until the `atfork' handlers have completed. By that time, the hooks will have been reset as well, so that mALLOc() can be used again. */ (void) mutex_lock (&list_lock); (void) mutex_unlock (&list_lock); return __libc_malloc (sz); } } static void free_atfork (void *mem, const void *caller) { mstate ar_ptr; mchunkptr p; /* chunk corresponding to mem */ if (mem == 0) /* free(0) has no effect */ return; p = mem2chunk (mem); /* do not bother to replicate free_check here */ if (chunk_is_mmapped (p)) /* release mmapped memory. */ { munmap_chunk (p); return; } ar_ptr = arena_for_chunk (p); _int_free (ar_ptr, p, thread_arena == ATFORK_ARENA_PTR); } /* Counter for number of times the list is locked by the same thread. */ static unsigned int atfork_recursive_cntr; /* The following two functions are registered via thread_atfork() to make sure that the mutexes remain in a consistent state in the fork()ed version of a thread. Also adapt the malloc and free hooks temporarily, because the `atfork' handler mechanism may use malloc/free internally (e.g. in LinuxThreads). */ static void ptmalloc_lock_all (void) { mstate ar_ptr; if (__malloc_initialized < 1) return; /* We do not acquire free_list_lock here because we completely reconstruct free_list in ptmalloc_unlock_all2. */ if (mutex_trylock (&list_lock)) { if (thread_arena == ATFORK_ARENA_PTR) /* This is the same thread which already locks the global list. Just bump the counter. */ goto out; /* This thread has to wait its turn. */ (void) mutex_lock (&list_lock); } for (ar_ptr = &main_arena;; ) { (void) mutex_lock (&ar_ptr->mutex); ar_ptr = ar_ptr->next; if (ar_ptr == &main_arena) break; } save_malloc_hook = __malloc_hook; save_free_hook = __free_hook; __malloc_hook = malloc_atfork; __free_hook = free_atfork; /* Only the current thread may perform malloc/free calls now. save_arena will be reattached to the current thread, in ptmalloc_lock_all, so save_arena->attached_threads is not updated. */ save_arena = thread_arena; thread_arena = ATFORK_ARENA_PTR; out: ++atfork_recursive_cntr; } static void ptmalloc_unlock_all (void) { mstate ar_ptr; if (__malloc_initialized < 1) return; if (--atfork_recursive_cntr != 0) return; /* Replace ATFORK_ARENA_PTR with save_arena. save_arena->attached_threads was not changed in ptmalloc_lock_all and is still correct. */ thread_arena = save_arena; __malloc_hook = save_malloc_hook; __free_hook = save_free_hook; for (ar_ptr = &main_arena;; ) { (void) mutex_unlock (&ar_ptr->mutex); ar_ptr = ar_ptr->next; if (ar_ptr == &main_arena) break; } (void) mutex_unlock (&list_lock); } # ifdef __linux__ /* In NPTL, unlocking a mutex in the child process after a fork() is currently unsafe, whereas re-initializing it is safe and does not leak resources. Therefore, a special atfork handler is installed for the child. */ static void ptmalloc_unlock_all2 (void) { mstate ar_ptr; if (__malloc_initialized < 1) return; thread_arena = save_arena; __malloc_hook = save_malloc_hook; __free_hook = save_free_hook; /* Push all arenas to the free list, except save_arena, which is attached to the current thread. */ mutex_init (&free_list_lock); if (save_arena != NULL) ((mstate) save_arena)->attached_threads = 1; free_list = NULL; for (ar_ptr = &main_arena;; ) { mutex_init (&ar_ptr->mutex); if (ar_ptr != save_arena) { /* This arena is no longer attached to any thread. */ ar_ptr->attached_threads = 0; ar_ptr->next_free = free_list; free_list = ar_ptr; } ar_ptr = ar_ptr->next; if (ar_ptr == &main_arena) break; } mutex_init (&list_lock); atfork_recursive_cntr = 0; } # else # define ptmalloc_unlock_all2 ptmalloc_unlock_all # endif #endif /* !NO_THREADS */ /* Initialization routine. */ #include extern char **_environ; static char * internal_function next_env_entry (char ***position) { char **current = *position; char *result = NULL; while (*current != NULL) { if (__builtin_expect ((*current)[0] == 'M', 0) && (*current)[1] == 'A' && (*current)[2] == 'L' && (*current)[3] == 'L' && (*current)[4] == 'O' && (*current)[5] == 'C' && (*current)[6] == '_') { result = &(*current)[7]; /* Save current position for next visit. */ *position = ++current; break; } ++current; } return result; } #ifdef SHARED static void * __failing_morecore (ptrdiff_t d) { return (void *) MORECORE_FAILURE; } extern struct dl_open_hook *_dl_open_hook; libc_hidden_proto (_dl_open_hook); #endif static void ptmalloc_init (void) { if (__malloc_initialized >= 0) return; __malloc_initialized = 0; #ifdef SHARED /* In case this libc copy is in a non-default namespace, never use brk. Likewise if dlopened from statically linked program. */ Dl_info di; struct link_map *l; if (_dl_open_hook != NULL || (_dl_addr (ptmalloc_init, &di, &l, NULL) != 0 && l->l_ns != LM_ID_BASE)) __morecore = __failing_morecore; #endif thread_arena = &main_arena; thread_atfork (ptmalloc_lock_all, ptmalloc_unlock_all, ptmalloc_unlock_all2); const char *s = NULL; if (__glibc_likely (_environ != NULL)) { char **runp = _environ; char *envline; while (__builtin_expect ((envline = next_env_entry (&runp)) != NULL, 0)) { size_t len = strcspn (envline, "="); if (envline[len] != '=') /* This is a "MALLOC_" variable at the end of the string without a '=' character. Ignore it since otherwise we will access invalid memory below. */ continue; switch (len) { case 6: if (memcmp (envline, "CHECK_", 6) == 0) s = &envline[7]; break; case 8: if (!__builtin_expect (__libc_enable_secure, 0)) { if (memcmp (envline, "TOP_PAD_", 8) == 0) __libc_mallopt (M_TOP_PAD, atoi (&envline[9])); else if (memcmp (envline, "PERTURB_", 8) == 0) __libc_mallopt (M_PERTURB, atoi (&envline[9])); } break; case 9: if (!__builtin_expect (__libc_enable_secure, 0)) { if (memcmp (envline, "MMAP_MAX_", 9) == 0) __libc_mallopt (M_MMAP_MAX, atoi (&envline[10])); else if (memcmp (envline, "ARENA_MAX", 9) == 0) __libc_mallopt (M_ARENA_MAX, atoi (&envline[10])); } break; case 10: if (!__builtin_expect (__libc_enable_secure, 0)) { if (memcmp (envline, "ARENA_TEST", 10) == 0) __libc_mallopt (M_ARENA_TEST, atoi (&envline[11])); } break; case 15: if (!__builtin_expect (__libc_enable_secure, 0)) { if (memcmp (envline, "TRIM_THRESHOLD_", 15) == 0) __libc_mallopt (M_TRIM_THRESHOLD, atoi (&envline[16])); else if (memcmp (envline, "MMAP_THRESHOLD_", 15) == 0) __libc_mallopt (M_MMAP_THRESHOLD, atoi (&envline[16])); } break; default: break; } } } if (s && s[0]) { __libc_mallopt (M_CHECK_ACTION, (int) (s[0] - '0')); if (check_action != 0) __malloc_check_init (); } void (*hook) (void) = atomic_forced_read (__malloc_initialize_hook); if (hook != NULL) (*hook)(); __malloc_initialized = 1; } /* There are platforms (e.g. Hurd) with a link-time hook mechanism. */ #ifdef thread_atfork_static thread_atfork_static (ptmalloc_lock_all, ptmalloc_unlock_all, \ ptmalloc_unlock_all2) #endif /* Managing heaps and arenas (for concurrent threads) */ #if MALLOC_DEBUG > 1 /* Print the complete contents of a single heap to stderr. */ static void dump_heap (heap_info *heap) { char *ptr; mchunkptr p; fprintf (stderr, "Heap %p, size %10lx:\n", heap, (long) heap->size); ptr = (heap->ar_ptr != (mstate) (heap + 1)) ? (char *) (heap + 1) : (char *) (heap + 1) + sizeof (struct malloc_state); p = (mchunkptr) (((unsigned long) ptr + MALLOC_ALIGN_MASK) & ~MALLOC_ALIGN_MASK); for (;; ) { fprintf (stderr, "chunk %p size %10lx", p, (long) p->size); if (p == top (heap->ar_ptr)) { fprintf (stderr, " (top)\n"); break; } else if (p->size == (0 | PREV_INUSE)) { fprintf (stderr, " (fence)\n"); break; } fprintf (stderr, "\n"); p = next_chunk (p); } } #endif /* MALLOC_DEBUG > 1 */ /* If consecutive mmap (0, HEAP_MAX_SIZE << 1, ...) calls return decreasing addresses as opposed to increasing, new_heap would badly fragment the address space. In that case remember the second HEAP_MAX_SIZE part aligned to HEAP_MAX_SIZE from last mmap (0, HEAP_MAX_SIZE << 1, ...) call (if it is already aligned) and try to reuse it next time. We need no locking for it, as kernel ensures the atomicity for us - worst case we'll call mmap (addr, HEAP_MAX_SIZE, ...) for some value of addr in multiple threads, but only one will succeed. */ static char *aligned_heap_area; /* Create a new heap. size is automatically rounded up to a multiple of the page size. */ static heap_info * internal_function new_heap (size_t size, size_t top_pad) { size_t pagesize = GLRO (dl_pagesize); char *p1, *p2; unsigned long ul; heap_info *h; if (size + top_pad < HEAP_MIN_SIZE) size = HEAP_MIN_SIZE; else if (size + top_pad <= HEAP_MAX_SIZE) size += top_pad; else if (size > HEAP_MAX_SIZE) return 0; else size = HEAP_MAX_SIZE; size = ALIGN_UP (size, pagesize); /* A memory region aligned to a multiple of HEAP_MAX_SIZE is needed. No swap space needs to be reserved for the following large mapping (on Linux, this is the case for all non-writable mappings anyway). */ p2 = MAP_FAILED; if (aligned_heap_area) { p2 = (char *) MMAP (aligned_heap_area, HEAP_MAX_SIZE, PROT_NONE, MAP_NORESERVE); aligned_heap_area = NULL; if (p2 != MAP_FAILED && ((unsigned long) p2 & (HEAP_MAX_SIZE - 1))) { __munmap (p2, HEAP_MAX_SIZE); p2 = MAP_FAILED; } } if (p2 == MAP_FAILED) { p1 = (char *) MMAP (0, HEAP_MAX_SIZE << 1, PROT_NONE, MAP_NORESERVE); if (p1 != MAP_FAILED) { p2 = (char *) (((unsigned long) p1 + (HEAP_MAX_SIZE - 1)) & ~(HEAP_MAX_SIZE - 1)); ul = p2 - p1; if (ul) __munmap (p1, ul); else aligned_heap_area = p2 + HEAP_MAX_SIZE; __munmap (p2 + HEAP_MAX_SIZE, HEAP_MAX_SIZE - ul); } else { /* Try to take the chance that an allocation of only HEAP_MAX_SIZE is already aligned. */ p2 = (char *) MMAP (0, HEAP_MAX_SIZE, PROT_NONE, MAP_NORESERVE); if (p2 == MAP_FAILED) return 0; if ((unsigned long) p2 & (HEAP_MAX_SIZE - 1)) { __munmap (p2, HEAP_MAX_SIZE); return 0; } } } if (__mprotect (p2, size, PROT_READ | PROT_WRITE) != 0) { __munmap (p2, HEAP_MAX_SIZE); return 0; } h = (heap_info *) p2; h->size = size; h->mprotect_size = size; LIBC_PROBE (memory_heap_new, 2, h, h->size); return h; } /* Grow a heap. size is automatically rounded up to a multiple of the page size. */ static int grow_heap (heap_info *h, long diff) { size_t pagesize = GLRO (dl_pagesize); long new_size; diff = ALIGN_UP (diff, pagesize); new_size = (long) h->size + diff; if ((unsigned long) new_size > (unsigned long) HEAP_MAX_SIZE) return -1; if ((unsigned long) new_size > h->mprotect_size) { if (__mprotect ((char *) h + h->mprotect_size, (unsigned long) new_size - h->mprotect_size, PROT_READ | PROT_WRITE) != 0) return -2; h->mprotect_size = new_size; } h->size = new_size; LIBC_PROBE (memory_heap_more, 2, h, h->size); return 0; } /* Shrink a heap. */ static int shrink_heap (heap_info *h, long diff) { long new_size; new_size = (long) h->size - diff; if (new_size < (long) sizeof (*h)) return -1; /* Try to re-map the extra heap space freshly to save memory, and make it inaccessible. See malloc-sysdep.h to know when this is true. */ if (__glibc_unlikely (check_may_shrink_heap ())) { if ((char *) MMAP ((char *) h + new_size, diff, PROT_NONE, MAP_FIXED) == (char *) MAP_FAILED) return -2; h->mprotect_size = new_size; } else __madvise ((char *) h + new_size, diff, MADV_DONTNEED); /*fprintf(stderr, "shrink %p %08lx\n", h, new_size);*/ h->size = new_size; LIBC_PROBE (memory_heap_less, 2, h, h->size); return 0; } /* Delete a heap. */ #define delete_heap(heap) \ do { \ if ((char *) (heap) + HEAP_MAX_SIZE == aligned_heap_area) \ aligned_heap_area = NULL; \ __munmap ((char *) (heap), HEAP_MAX_SIZE); \ } while (0) static int internal_function heap_trim (heap_info *heap, size_t pad) { mstate ar_ptr = heap->ar_ptr; unsigned long pagesz = GLRO (dl_pagesize); mchunkptr top_chunk = top (ar_ptr), p, bck, fwd; heap_info *prev_heap; long new_size, top_size, top_area, extra, prev_size, misalign; /* Can this heap go away completely? */ while (top_chunk == chunk_at_offset (heap, sizeof (*heap))) { prev_heap = heap->prev; prev_size = prev_heap->size - (MINSIZE - 2 * SIZE_SZ); p = chunk_at_offset (prev_heap, prev_size); /* fencepost must be properly aligned. */ misalign = ((long) p) & MALLOC_ALIGN_MASK; p = chunk_at_offset (prev_heap, prev_size - misalign); assert (p->size == (0 | PREV_INUSE)); /* must be fencepost */ p = prev_chunk (p); new_size = chunksize (p) + (MINSIZE - 2 * SIZE_SZ) + misalign; assert (new_size > 0 && new_size < (long) (2 * MINSIZE)); if (!prev_inuse (p)) new_size += p->prev_size; assert (new_size > 0 && new_size < HEAP_MAX_SIZE); if (new_size + (HEAP_MAX_SIZE - prev_heap->size) < pad + MINSIZE + pagesz) break; ar_ptr->system_mem -= heap->size; arena_mem -= heap->size; LIBC_PROBE (memory_heap_free, 2, heap, heap->size); delete_heap (heap); heap = prev_heap; if (!prev_inuse (p)) /* consolidate backward */ { p = prev_chunk (p); unlink (ar_ptr, p, bck, fwd); } assert (((unsigned long) ((char *) p + new_size) & (pagesz - 1)) == 0); assert (((char *) p + new_size) == ((char *) heap + heap->size)); top (ar_ptr) = top_chunk = p; set_head (top_chunk, new_size | PREV_INUSE); /*check_chunk(ar_ptr, top_chunk);*/ } /* Uses similar logic for per-thread arenas as the main arena with systrim and _int_free by preserving the top pad and rounding down to the nearest page. */ top_size = chunksize (top_chunk); if ((unsigned long)(top_size) < (unsigned long)(mp_.trim_threshold)) return 0; top_area = top_size - MINSIZE - 1; if (top_area < 0 || (size_t) top_area <= pad) return 0; /* Release in pagesize units and round down to the nearest page. */ extra = ALIGN_DOWN(top_area - pad, pagesz); if (extra == 0) return 0; /* Try to shrink. */ if (shrink_heap (heap, extra) != 0) return 0; ar_ptr->system_mem -= extra; arena_mem -= extra; /* Success. Adjust top accordingly. */ set_head (top_chunk, (top_size - extra) | PREV_INUSE); /*check_chunk(ar_ptr, top_chunk);*/ return 1; } /* Create a new arena with initial size "size". */ /* If REPLACED_ARENA is not NULL, detach it from this thread. Must be called while free_list_lock is held. */ static void detach_arena (mstate replaced_arena) { if (replaced_arena != NULL) { assert (replaced_arena->attached_threads > 0); /* The current implementation only detaches from main_arena in case of allocation failure. This means that it is likely not beneficial to put the arena on free_list even if the reference count reaches zero. */ --replaced_arena->attached_threads; } } static mstate _int_new_arena (size_t size) { mstate a; heap_info *h; char *ptr; unsigned long misalign; h = new_heap (size + (sizeof (*h) + sizeof (*a) + MALLOC_ALIGNMENT), mp_.top_pad); if (!h) { /* Maybe size is too large to fit in a single heap. So, just try to create a minimally-sized arena and let _int_malloc() attempt to deal with the large request via mmap_chunk(). */ h = new_heap (sizeof (*h) + sizeof (*a) + MALLOC_ALIGNMENT, mp_.top_pad); if (!h) return 0; } a = h->ar_ptr = (mstate) (h + 1); malloc_init_state (a); a->attached_threads = 1; /*a->next = NULL;*/ a->system_mem = a->max_system_mem = h->size; arena_mem += h->size; /* Set up the top chunk, with proper alignment. */ ptr = (char *) (a + 1); misalign = (unsigned long) chunk2mem (ptr) & MALLOC_ALIGN_MASK; if (misalign > 0) ptr += MALLOC_ALIGNMENT - misalign; top (a) = (mchunkptr) ptr; set_head (top (a), (((char *) h + h->size) - ptr) | PREV_INUSE); LIBC_PROBE (memory_arena_new, 2, a, size); mstate replaced_arena = thread_arena; thread_arena = a; mutex_init (&a->mutex); (void) mutex_lock (&list_lock); /* Add the new arena to the global list. */ a->next = main_arena.next; /* FIXME: The barrier is an attempt to synchronize with read access in reused_arena, which does not acquire list_lock while traversing the list. */ atomic_write_barrier (); main_arena.next = a; (void) mutex_unlock (&list_lock); (void) mutex_lock (&free_list_lock); detach_arena (replaced_arena); (void) mutex_unlock (&free_list_lock); /* Lock this arena. NB: Another thread may have been attached to this arena because the arena is now accessible from the main_arena.next list and could have been picked by reused_arena. This can only happen for the last arena created (before the arena limit is reached). At this point, some arena has to be attached to two threads. We could acquire the arena lock before list_lock to make it less likely that reused_arena picks this new arena, but this could result in a deadlock with ptmalloc_lock_all. */ (void) mutex_lock (&a->mutex); return a; } /* Remove an arena from free_list. The arena may be in use because it was attached concurrently to a thread by reused_arena below. */ static mstate get_free_list (void) { mstate replaced_arena = thread_arena; mstate result = free_list; if (result != NULL) { (void) mutex_lock (&free_list_lock); result = free_list; if (result != NULL) { free_list = result->next_free; /* The arena will be attached to this thread. */ ++result->attached_threads; detach_arena (replaced_arena); } (void) mutex_unlock (&free_list_lock); if (result != NULL) { LIBC_PROBE (memory_arena_reuse_free_list, 1, result); (void) mutex_lock (&result->mutex); thread_arena = result; } } return result; } /* 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. */ static mstate reused_arena (mstate avoid_arena) { mstate result; /* FIXME: Access to next_to_use suffers from data races. */ static mstate next_to_use; if (next_to_use == NULL) next_to_use = &main_arena; /* Iterate over all arenas (including those linked from free_list). */ result = next_to_use; do { if (!arena_is_corrupt (result) && !mutex_trylock (&result->mutex)) goto out; /* FIXME: This is a data race, see _int_new_arena. */ result = result->next; } while (result != next_to_use); /* Avoid AVOID_ARENA as we have already failed to allocate memory in that arena and it is currently locked. */ if (result == avoid_arena) result = result->next; /* Make sure that the arena we get is not corrupted. */ mstate begin = result; while (arena_is_corrupt (result) || result == avoid_arena) { result = result->next; if (result == begin) break; } /* We could not find any arena that was either not corrupted or not the one we wanted to avoid. */ if (result == begin || result == avoid_arena) return NULL; /* No arena available without contention. Wait for the next in line. */ LIBC_PROBE (memory_arena_reuse_wait, 3, &result->mutex, result, 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. */ { /* Update the arena thread attachment counters. */ mstate replaced_arena = thread_arena; (void) mutex_lock (&free_list_lock); detach_arena (replaced_arena); ++result->attached_threads; (void) mutex_unlock (&free_list_lock); } LIBC_PROBE (memory_arena_reuse, 2, result, avoid_arena); thread_arena = result; next_to_use = result->next; return result; } static mstate internal_function arena_get2 (size_t size, mstate avoid_arena) { mstate a; static size_t narenas_limit; a = get_free_list (); if (a == NULL) { /* Nothing immediately available, so generate a new arena. */ if (narenas_limit == 0) { if (mp_.arena_max != 0) narenas_limit = mp_.arena_max; else if (narenas > mp_.arena_test) { int n = __get_nprocs (); if (n >= 1) narenas_limit = NARENAS_FROM_NCORES (n); else /* We have no information about the system. Assume two cores. */ narenas_limit = NARENAS_FROM_NCORES (2); } } repeat:; size_t n = narenas; /* NB: the following depends on the fact that (size_t)0 - 1 is a very large number and that the underflow is OK. If arena_max is set the value of arena_test is irrelevant. If arena_test is set but narenas is not yet larger or equal to arena_test narenas_limit is 0. There is no possibility for narenas to be too big for the test to always fail since there is not enough address space to create that many arenas. */ if (__glibc_unlikely (n <= narenas_limit - 1)) { if (catomic_compare_and_exchange_bool_acq (&narenas, n + 1, n)) goto repeat; a = _int_new_arena (size); if (__glibc_unlikely (a == NULL)) catomic_decrement (&narenas); } else a = reused_arena (avoid_arena); } return a; } /* If we don't have the main arena, then maybe the failure is due to running out of mmapped areas, so we can try allocating on the main arena. Otherwise, it is likely that sbrk() has failed and there is still a chance to mmap(), so try one of the other arenas. */ static mstate arena_get_retry (mstate ar_ptr, size_t bytes) { LIBC_PROBE (memory_arena_retry, 2, bytes, ar_ptr); if (ar_ptr != &main_arena) { (void) mutex_unlock (&ar_ptr->mutex); /* Don't touch the main arena if it is corrupt. */ if (arena_is_corrupt (&main_arena)) return NULL; ar_ptr = &main_arena; (void) mutex_lock (&ar_ptr->mutex); } else { (void) mutex_unlock (&ar_ptr->mutex); ar_ptr = arena_get2 (bytes, ar_ptr); } return ar_ptr; } static void __attribute__ ((section ("__libc_thread_freeres_fn"))) arena_thread_freeres (void) { mstate a = thread_arena; thread_arena = NULL; if (a != NULL) { (void) mutex_lock (&free_list_lock); /* If this was the last attached thread for this arena, put the arena on the free list. */ assert (a->attached_threads > 0); if (--a->attached_threads == 0) { a->next_free = free_list; free_list = a; } (void) mutex_unlock (&free_list_lock); } } text_set_element (__libc_thread_subfreeres, arena_thread_freeres); /* * Local variables: * c-basic-offset: 2 * End: */