/* Malloc implementation for multiple threads without lock contention. Copyright (C) 2001,2002,2003,2004,2005,2006,2007,2009,2010,2011 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, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ #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. */ #ifndef THREAD_STATS #define THREAD_STATS 0 #endif /* If THREAD_STATS is non-zero, some statistics on mutex locking are computed. */ /***************************************************************************/ #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 tsd_key_t arena_key; static mutex_t list_lock = MUTEX_INITIALIZER; #ifdef PER_THREAD static size_t narenas = 1; static mstate free_list; #endif #if THREAD_STATS static int stat_n_heaps; #define THREAD_STAT(x) x #else #define THREAD_STAT(x) do ; while(0) #endif /* 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 { \ arena_lookup(ptr); \ arena_lock(ptr, size); \ } while(0) #define arena_lookup(ptr) do { \ void *vptr = NULL; \ ptr = (mstate)tsd_getspecific(arena_key, vptr); \ } while(0) #ifdef PER_THREAD # define arena_lock(ptr, size) do { \ if(ptr) \ (void)mutex_lock(&ptr->mutex); \ else \ ptr = arena_get2(ptr, (size)); \ } while(0) #else # define arena_lock(ptr, size) do { \ if(ptr && !mutex_trylock(&ptr->mutex)) { \ THREAD_STAT(++(ptr->stat_lock_direct)); \ } else \ ptr = arena_get2(ptr, (size)); \ } while(0) #endif /* 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) /**************************************************************************/ /* atfork support. */ static __malloc_ptr_t (*save_malloc_hook) (size_t __size, __const __malloc_ptr_t); static void (*save_free_hook) (__malloc_ptr_t __ptr, __const __malloc_ptr_t); 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 *vptr = NULL; void *victim; tsd_getspecific(arena_key, vptr); if(vptr == 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 public_mALLOc(sz); } } static void free_atfork(void* mem, const void *caller) { void *vptr = NULL; 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); tsd_getspecific(arena_key, vptr); _int_free(ar_ptr, p, vptr == 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; if (mutex_trylock(&list_lock)) { void *my_arena; tsd_getspecific(arena_key, my_arena); if (my_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. */ tsd_getspecific(arena_key, save_arena); tsd_setspecific(arena_key, 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; tsd_setspecific(arena_key, 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; tsd_setspecific(arena_key, save_arena); __malloc_hook = save_malloc_hook; __free_hook = save_free_hook; #ifdef PER_THREAD free_list = NULL; #endif for(ar_ptr = &main_arena;;) { mutex_init(&ar_ptr->mutex); #ifdef PER_THREAD if (ar_ptr != save_arena) { ar_ptr->next_free = free_list; free_list = ar_ptr; } #endif 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 /* 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 tsd_key_create(&arena_key, NULL); tsd_setspecific(arena_key, (void *)&main_arena); thread_atfork(ptmalloc_lock_all, ptmalloc_unlock_all, ptmalloc_unlock_all2); const char *s = NULL; if (__builtin_expect (_environ != NULL, 1)) { 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) mALLOPt(M_TOP_PAD, atoi(&envline[9])); else if (memcmp (envline, "PERTURB_", 8) == 0) mALLOPt(M_PERTURB, atoi(&envline[9])); } break; case 9: if (! __builtin_expect (__libc_enable_secure, 0)) { if (memcmp (envline, "MMAP_MAX_", 9) == 0) mALLOPt(M_MMAP_MAX, atoi(&envline[10])); #ifdef PER_THREAD else if (memcmp (envline, "ARENA_MAX", 9) == 0) mALLOPt(M_ARENA_MAX, atoi(&envline[10])); #endif } break; #ifdef PER_THREAD case 10: if (! __builtin_expect (__libc_enable_secure, 0)) { if (memcmp (envline, "ARENA_TEST", 10) == 0) mALLOPt(M_ARENA_TEST, atoi(&envline[11])); } break; #endif case 15: if (! __builtin_expect (__libc_enable_secure, 0)) { if (memcmp (envline, "TRIM_THRESHOLD_", 15) == 0) mALLOPt(M_TRIM_THRESHOLD, atoi(&envline[16])); else if (memcmp (envline, "MMAP_THRESHOLD_", 15) == 0) mALLOPt(M_MMAP_THRESHOLD, atoi(&envline[16])); } break; default: break; } } } if(s && s[0]) { mALLOPt(M_CHECK_ACTION, (int)(s[0] - '0')); if (check_action != 0) __malloc_check_init(); } void (*hook) (void) = force_reg (__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 page_mask = GLRO(dl_pagesize) - 1; 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 = (size + page_mask) & ~page_mask; /* 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_PRIVATE|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_PRIVATE|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_PRIVATE|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; THREAD_STAT(stat_n_heaps++); 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 page_mask = GLRO(dl_pagesize) - 1; long new_size; diff = (diff + page_mask) & ~page_mask; 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; 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. */ if (__builtin_expect (__libc_enable_secure, 0)) { if((char *)MMAP((char *)h + new_size, diff, PROT_NONE, MAP_PRIVATE|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; 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, extra; /* Can this heap go away completely? */ while(top_chunk == chunk_at_offset(heap, sizeof(*heap))) { prev_heap = heap->prev; p = chunk_at_offset(prev_heap, prev_heap->size - (MINSIZE-2*SIZE_SZ)); assert(p->size == (0|PREV_INUSE)); /* must be fencepost */ p = prev_chunk(p); new_size = chunksize(p) + (MINSIZE-2*SIZE_SZ); assert(new_size>0 && new_size<(long)(2*MINSIZE)); if(!prev_inuse(p)) new_size += p->prev_size; assert(new_size>0 && new_sizesize) < pad + MINSIZE + pagesz) break; ar_ptr->system_mem -= heap->size; arena_mem -= heap->size; delete_heap(heap); heap = prev_heap; if(!prev_inuse(p)) { /* consolidate backward */ p = prev_chunk(p); unlink(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);*/ } top_size = chunksize(top_chunk); extra = (top_size - pad - MINSIZE - 1) & ~(pagesz - 1); if(extra < (long)pagesz) 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". */ 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->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); tsd_setspecific(arena_key, (void *)a); mutex_init(&a->mutex); (void)mutex_lock(&a->mutex); #ifdef PER_THREAD (void)mutex_lock(&list_lock); #endif /* Add the new arena to the global list. */ a->next = main_arena.next; atomic_write_barrier (); main_arena.next = a; #ifdef PER_THREAD (void)mutex_unlock(&list_lock); #endif THREAD_STAT(++(a->stat_lock_loop)); return a; } #ifdef PER_THREAD static mstate get_free_list (void) { mstate result = free_list; if (result != NULL) { (void)mutex_lock(&list_lock); result = free_list; if (result != NULL) free_list = result->next_free; (void)mutex_unlock(&list_lock); if (result != NULL) { (void)mutex_lock(&result->mutex); tsd_setspecific(arena_key, (void *)result); THREAD_STAT(++(result->stat_lock_loop)); } } return result; } static mstate reused_arena (void) { mstate result; static mstate next_to_use; if (next_to_use == NULL) next_to_use = &main_arena; result = next_to_use; do { if (!mutex_trylock(&result->mutex)) goto out; result = result->next; } while (result != next_to_use); /* No arena available. Wait for the next in line. */ (void)mutex_lock(&result->mutex); out: tsd_setspecific(arena_key, (void *)result); THREAD_STAT(++(result->stat_lock_loop)); next_to_use = result->next; return result; } #endif static mstate internal_function arena_get2(mstate a_tsd, size_t size) { mstate a; #ifdef PER_THREAD 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 { 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; if (__builtin_expect (n <= mp_.arena_test || n < narenas_limit, 0)) { if (catomic_compare_and_exchange_bool_acq(&narenas, n + 1, n)) goto repeat; a = _int_new_arena (size); if (__builtin_expect (a != NULL, 1)) return a; catomic_decrement(&narenas); } a = reused_arena (); } #else if(!a_tsd) a = a_tsd = &main_arena; else { a = a_tsd->next; if(!a) { /* This can only happen while initializing the new arena. */ (void)mutex_lock(&main_arena.mutex); THREAD_STAT(++(main_arena.stat_lock_wait)); return &main_arena; } } /* Check the global, circularly linked list for available arenas. */ bool retried = false; repeat: do { if(!mutex_trylock(&a->mutex)) { if (retried) (void)mutex_unlock(&list_lock); THREAD_STAT(++(a->stat_lock_loop)); tsd_setspecific(arena_key, (void *)a); return a; } a = a->next; } while(a != a_tsd); /* If not even the list_lock can be obtained, try again. This can happen during `atfork', or for example on systems where thread creation makes it temporarily impossible to obtain _any_ locks. */ if(!retried && mutex_trylock(&list_lock)) { /* We will block to not run in a busy loop. */ (void)mutex_lock(&list_lock); /* Since we blocked there might be an arena available now. */ retried = true; a = a_tsd; goto repeat; } /* Nothing immediately available, so generate a new arena. */ a = _int_new_arena(size); (void)mutex_unlock(&list_lock); #endif return a; } #ifdef PER_THREAD static void __attribute__ ((section ("__libc_thread_freeres_fn"))) arena_thread_freeres (void) { void *vptr = NULL; mstate a = tsd_getspecific(arena_key, vptr); tsd_setspecific(arena_key, NULL); if (a != NULL) { (void)mutex_lock(&list_lock); a->next_free = free_list; free_list = a; (void)mutex_unlock(&list_lock); } } text_set_element (__libc_thread_subfreeres, arena_thread_freeres); #endif /* * Local variables: * c-basic-offset: 2 * End: */