1 /* Malloc implementation for multiple threads without lock contention.
2 Copyright (C) 2001-2021 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Wolfram Gloger <wg@malloc.de>, 2001.
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public License as
8 published by the Free Software Foundation; either version 2.1 of the
9 License, or (at your option) any later version.
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; see the file COPYING.LIB. If
18 not, see <https://www.gnu.org/licenses/>. */
23 # define TUNABLE_NAMESPACE malloc
25 #include <elf/dl-tunables.h>
27 /* Compile-time constants. */
29 #define HEAP_MIN_SIZE (32 * 1024)
31 # ifdef DEFAULT_MMAP_THRESHOLD_MAX
32 # define HEAP_MAX_SIZE (2 * DEFAULT_MMAP_THRESHOLD_MAX)
34 # define HEAP_MAX_SIZE (1024 * 1024) /* must be a power of two */
38 /* HEAP_MIN_SIZE and HEAP_MAX_SIZE limit the size of mmap()ed heaps
39 that are dynamically created for multi-threaded programs. The
40 maximum size must be a power of two, for fast determination of
41 which heap belongs to a chunk. It should be much larger than the
42 mmap threshold, so that requests with a size just below that
43 threshold can be fulfilled without creating too many heaps. */
45 /***************************************************************************/
47 #define top(ar_ptr) ((ar_ptr)->top)
49 /* A heap is a single contiguous memory region holding (coalesceable)
50 malloc_chunks. It is allocated with mmap() and always starts at an
51 address aligned to HEAP_MAX_SIZE. */
53 typedef struct _heap_info
55 mstate ar_ptr
; /* Arena for this heap. */
56 struct _heap_info
*prev
; /* Previous heap. */
57 size_t size
; /* Current size in bytes. */
58 size_t mprotect_size
; /* Size in bytes that has been mprotected
59 PROT_READ|PROT_WRITE. */
60 /* Make sure the following data is properly aligned, particularly
61 that sizeof (heap_info) + 2 * SIZE_SZ is a multiple of
63 char pad
[-6 * SIZE_SZ
& MALLOC_ALIGN_MASK
];
66 /* Get a compile-time error if the heap_info padding is not correct
67 to make alignment work as expected in sYSMALLOc. */
68 extern int sanity_check_heap_info_alignment
[(sizeof (heap_info
)
69 + 2 * SIZE_SZ
) % MALLOC_ALIGNMENT
72 /* Thread specific data. */
74 static __thread mstate thread_arena attribute_tls_model_ie
;
76 /* Arena free list. free_list_lock synchronizes access to the
77 free_list variable below, and the next_free and attached_threads
78 members of struct malloc_state objects. No other locks must be
79 acquired after free_list_lock has been acquired. */
81 __libc_lock_define_initialized (static, free_list_lock
);
82 static size_t narenas
= 1;
83 static mstate free_list
;
85 /* list_lock prevents concurrent writes to the next member of struct
88 Read access to the next member is supposed to synchronize with the
89 atomic_write_barrier and the write to the next member in
90 _int_new_arena. This suffers from data races; see the FIXME
91 comments in _int_new_arena and reused_arena.
93 list_lock also prevents concurrent forks. At the time list_lock is
94 acquired, no arena lock must have been acquired, but it is
95 permitted to acquire arena locks subsequently, while list_lock is
97 __libc_lock_define_initialized (static, list_lock
);
99 /* Already initialized? */
100 int __malloc_initialized
= -1;
102 /**************************************************************************/
105 /* arena_get() acquires an arena and locks the corresponding mutex.
106 First, try the one last locked successfully by this thread. (This
107 is the common case and handled with a macro for speed.) Then, loop
108 once over the circularly linked list of arenas. If no arena is
109 readily available, create a new one. In this latter case, `size'
110 is just a hint as to how much memory will be required immediately
113 #define arena_get(ptr, size) do { \
114 ptr = thread_arena; \
115 arena_lock (ptr, size); \
118 #define arena_lock(ptr, size) do { \
120 __libc_lock_lock (ptr->mutex); \
122 ptr = arena_get2 ((size), NULL); \
125 /* find the heap and corresponding arena for a given ptr */
127 #define heap_for_ptr(ptr) \
128 ((heap_info *) ((unsigned long) (ptr) & ~(HEAP_MAX_SIZE - 1)))
129 #define arena_for_chunk(ptr) \
130 (chunk_main_arena (ptr) ? &main_arena : heap_for_ptr (ptr)->ar_ptr)
133 /**************************************************************************/
135 /* atfork support. */
137 /* The following three functions are called around fork from a
138 multi-threaded process. We do not use the general fork handler
139 mechanism to make sure that our handlers are the last ones being
140 called, so that other fork handlers can use the malloc
144 __malloc_fork_lock_parent (void)
146 if (__malloc_initialized
< 1)
149 /* We do not acquire free_list_lock here because we completely
150 reconstruct free_list in __malloc_fork_unlock_child. */
152 __libc_lock_lock (list_lock
);
154 for (mstate ar_ptr
= &main_arena
;; )
156 __libc_lock_lock (ar_ptr
->mutex
);
157 ar_ptr
= ar_ptr
->next
;
158 if (ar_ptr
== &main_arena
)
164 __malloc_fork_unlock_parent (void)
166 if (__malloc_initialized
< 1)
169 for (mstate ar_ptr
= &main_arena
;; )
171 __libc_lock_unlock (ar_ptr
->mutex
);
172 ar_ptr
= ar_ptr
->next
;
173 if (ar_ptr
== &main_arena
)
176 __libc_lock_unlock (list_lock
);
180 __malloc_fork_unlock_child (void)
182 if (__malloc_initialized
< 1)
185 /* Push all arenas to the free list, except thread_arena, which is
186 attached to the current thread. */
187 __libc_lock_init (free_list_lock
);
188 if (thread_arena
!= NULL
)
189 thread_arena
->attached_threads
= 1;
191 for (mstate ar_ptr
= &main_arena
;; )
193 __libc_lock_init (ar_ptr
->mutex
);
194 if (ar_ptr
!= thread_arena
)
196 /* This arena is no longer attached to any thread. */
197 ar_ptr
->attached_threads
= 0;
198 ar_ptr
->next_free
= free_list
;
201 ar_ptr
= ar_ptr
->next
;
202 if (ar_ptr
== &main_arena
)
206 __libc_lock_init (list_lock
);
211 TUNABLE_CALLBACK (set_mallopt_check
) (tunable_val_t
*valp
)
213 int32_t value
= (int32_t) valp
->numval
;
215 __malloc_check_init ();
218 # define TUNABLE_CALLBACK_FNDECL(__name, __type) \
219 static inline int do_ ## __name (__type value); \
221 TUNABLE_CALLBACK (__name) (tunable_val_t *valp) \
223 __type value = (__type) (valp)->numval; \
224 do_ ## __name (value); \
227 TUNABLE_CALLBACK_FNDECL (set_mmap_threshold
, size_t)
228 TUNABLE_CALLBACK_FNDECL (set_mmaps_max
, int32_t)
229 TUNABLE_CALLBACK_FNDECL (set_top_pad
, size_t)
230 TUNABLE_CALLBACK_FNDECL (set_perturb_byte
, int32_t)
231 TUNABLE_CALLBACK_FNDECL (set_trim_threshold
, size_t)
232 TUNABLE_CALLBACK_FNDECL (set_arena_max
, size_t)
233 TUNABLE_CALLBACK_FNDECL (set_arena_test
, size_t)
235 TUNABLE_CALLBACK_FNDECL (set_tcache_max
, size_t)
236 TUNABLE_CALLBACK_FNDECL (set_tcache_count
, size_t)
237 TUNABLE_CALLBACK_FNDECL (set_tcache_unsorted_limit
, size_t)
239 TUNABLE_CALLBACK_FNDECL (set_mxfast
, size_t)
241 /* Initialization routine. */
243 extern char **_environ
;
246 next_env_entry (char ***position
)
248 char **current
= *position
;
251 while (*current
!= NULL
)
253 if (__builtin_expect ((*current
)[0] == 'M', 0)
254 && (*current
)[1] == 'A'
255 && (*current
)[2] == 'L'
256 && (*current
)[3] == 'L'
257 && (*current
)[4] == 'O'
258 && (*current
)[5] == 'C'
259 && (*current
)[6] == '_')
261 result
= &(*current
)[7];
263 /* Save current position for next visit. */
264 *position
= ++current
;
277 #if defined(SHARED) || defined(USE_MTAG)
279 __failing_morecore (ptrdiff_t d
)
281 return (void *) MORECORE_FAILURE
;
286 extern struct dl_open_hook
*_dl_open_hook
;
287 libc_hidden_proto (_dl_open_hook
);
293 if (__malloc_initialized
>= 0)
296 __malloc_initialized
= 0;
299 if ((TUNABLE_GET_FULL (glibc
, mem
, tagging
, int32_t, NULL
) & 1) != 0)
301 /* If the tunable says that we should be using tagged memory
302 and that morecore does not support tagged regions, then
304 if (__MTAG_SBRK_UNTAGGED
)
305 __morecore
= __failing_morecore
;
308 mtag_mmap_flags
= __MTAG_MMAP_FLAGS
;
313 /* In case this libc copy is in a non-default namespace, never use
314 brk. Likewise if dlopened from statically linked program. The
315 generic sbrk implementation also enforces this, but it is not
318 __morecore
= __failing_morecore
;
321 thread_arena
= &main_arena
;
323 malloc_init_state (&main_arena
);
326 TUNABLE_GET (check
, int32_t, TUNABLE_CALLBACK (set_mallopt_check
));
327 TUNABLE_GET (top_pad
, size_t, TUNABLE_CALLBACK (set_top_pad
));
328 TUNABLE_GET (perturb
, int32_t, TUNABLE_CALLBACK (set_perturb_byte
));
329 TUNABLE_GET (mmap_threshold
, size_t, TUNABLE_CALLBACK (set_mmap_threshold
));
330 TUNABLE_GET (trim_threshold
, size_t, TUNABLE_CALLBACK (set_trim_threshold
));
331 TUNABLE_GET (mmap_max
, int32_t, TUNABLE_CALLBACK (set_mmaps_max
));
332 TUNABLE_GET (arena_max
, size_t, TUNABLE_CALLBACK (set_arena_max
));
333 TUNABLE_GET (arena_test
, size_t, TUNABLE_CALLBACK (set_arena_test
));
335 TUNABLE_GET (tcache_max
, size_t, TUNABLE_CALLBACK (set_tcache_max
));
336 TUNABLE_GET (tcache_count
, size_t, TUNABLE_CALLBACK (set_tcache_count
));
337 TUNABLE_GET (tcache_unsorted_limit
, size_t,
338 TUNABLE_CALLBACK (set_tcache_unsorted_limit
));
340 TUNABLE_GET (mxfast
, size_t, TUNABLE_CALLBACK (set_mxfast
));
342 const char *s
= NULL
;
343 if (__glibc_likely (_environ
!= NULL
))
345 char **runp
= _environ
;
348 while (__builtin_expect ((envline
= next_env_entry (&runp
)) != NULL
,
351 size_t len
= strcspn (envline
, "=");
353 if (envline
[len
] != '=')
354 /* This is a "MALLOC_" variable at the end of the string
355 without a '=' character. Ignore it since otherwise we
356 will access invalid memory below. */
362 if (memcmp (envline
, "CHECK_", 6) == 0)
366 if (!__builtin_expect (__libc_enable_secure
, 0))
368 if (memcmp (envline
, "TOP_PAD_", 8) == 0)
369 __libc_mallopt (M_TOP_PAD
, atoi (&envline
[9]));
370 else if (memcmp (envline
, "PERTURB_", 8) == 0)
371 __libc_mallopt (M_PERTURB
, atoi (&envline
[9]));
375 if (!__builtin_expect (__libc_enable_secure
, 0))
377 if (memcmp (envline
, "MMAP_MAX_", 9) == 0)
378 __libc_mallopt (M_MMAP_MAX
, atoi (&envline
[10]));
379 else if (memcmp (envline
, "ARENA_MAX", 9) == 0)
380 __libc_mallopt (M_ARENA_MAX
, atoi (&envline
[10]));
384 if (!__builtin_expect (__libc_enable_secure
, 0))
386 if (memcmp (envline
, "ARENA_TEST", 10) == 0)
387 __libc_mallopt (M_ARENA_TEST
, atoi (&envline
[11]));
391 if (!__builtin_expect (__libc_enable_secure
, 0))
393 if (memcmp (envline
, "TRIM_THRESHOLD_", 15) == 0)
394 __libc_mallopt (M_TRIM_THRESHOLD
, atoi (&envline
[16]));
395 else if (memcmp (envline
, "MMAP_THRESHOLD_", 15) == 0)
396 __libc_mallopt (M_MMAP_THRESHOLD
, atoi (&envline
[16]));
404 if (s
&& s
[0] != '\0' && s
[0] != '0')
405 __malloc_check_init ();
408 #if HAVE_MALLOC_INIT_HOOK
409 void (*hook
) (void) = atomic_forced_read (__malloc_initialize_hook
);
413 __malloc_initialized
= 1;
416 /* Managing heaps and arenas (for concurrent threads) */
420 /* Print the complete contents of a single heap to stderr. */
423 dump_heap (heap_info
*heap
)
428 fprintf (stderr
, "Heap %p, size %10lx:\n", heap
, (long) heap
->size
);
429 ptr
= (heap
->ar_ptr
!= (mstate
) (heap
+ 1)) ?
430 (char *) (heap
+ 1) : (char *) (heap
+ 1) + sizeof (struct malloc_state
);
431 p
= (mchunkptr
) (((unsigned long) ptr
+ MALLOC_ALIGN_MASK
) &
435 fprintf (stderr
, "chunk %p size %10lx", p
, (long) chunksize_nomask(p
));
436 if (p
== top (heap
->ar_ptr
))
438 fprintf (stderr
, " (top)\n");
441 else if (chunksize_nomask(p
) == (0 | PREV_INUSE
))
443 fprintf (stderr
, " (fence)\n");
446 fprintf (stderr
, "\n");
450 #endif /* MALLOC_DEBUG > 1 */
452 /* If consecutive mmap (0, HEAP_MAX_SIZE << 1, ...) calls return decreasing
453 addresses as opposed to increasing, new_heap would badly fragment the
454 address space. In that case remember the second HEAP_MAX_SIZE part
455 aligned to HEAP_MAX_SIZE from last mmap (0, HEAP_MAX_SIZE << 1, ...)
456 call (if it is already aligned) and try to reuse it next time. We need
457 no locking for it, as kernel ensures the atomicity for us - worst case
458 we'll call mmap (addr, HEAP_MAX_SIZE, ...) for some value of addr in
459 multiple threads, but only one will succeed. */
460 static char *aligned_heap_area
;
462 /* Create a new heap. size is automatically rounded up to a multiple
466 new_heap (size_t size
, size_t top_pad
)
468 size_t pagesize
= GLRO (dl_pagesize
);
473 if (size
+ top_pad
< HEAP_MIN_SIZE
)
474 size
= HEAP_MIN_SIZE
;
475 else if (size
+ top_pad
<= HEAP_MAX_SIZE
)
477 else if (size
> HEAP_MAX_SIZE
)
480 size
= HEAP_MAX_SIZE
;
481 size
= ALIGN_UP (size
, pagesize
);
483 /* A memory region aligned to a multiple of HEAP_MAX_SIZE is needed.
484 No swap space needs to be reserved for the following large
485 mapping (on Linux, this is the case for all non-writable mappings
488 if (aligned_heap_area
)
490 p2
= (char *) MMAP (aligned_heap_area
, HEAP_MAX_SIZE
, PROT_NONE
,
492 aligned_heap_area
= NULL
;
493 if (p2
!= MAP_FAILED
&& ((unsigned long) p2
& (HEAP_MAX_SIZE
- 1)))
495 __munmap (p2
, HEAP_MAX_SIZE
);
499 if (p2
== MAP_FAILED
)
501 p1
= (char *) MMAP (0, HEAP_MAX_SIZE
<< 1, PROT_NONE
, MAP_NORESERVE
);
502 if (p1
!= MAP_FAILED
)
504 p2
= (char *) (((unsigned long) p1
+ (HEAP_MAX_SIZE
- 1))
505 & ~(HEAP_MAX_SIZE
- 1));
510 aligned_heap_area
= p2
+ HEAP_MAX_SIZE
;
511 __munmap (p2
+ HEAP_MAX_SIZE
, HEAP_MAX_SIZE
- ul
);
515 /* Try to take the chance that an allocation of only HEAP_MAX_SIZE
516 is already aligned. */
517 p2
= (char *) MMAP (0, HEAP_MAX_SIZE
, PROT_NONE
, MAP_NORESERVE
);
518 if (p2
== MAP_FAILED
)
521 if ((unsigned long) p2
& (HEAP_MAX_SIZE
- 1))
523 __munmap (p2
, HEAP_MAX_SIZE
);
528 if (__mprotect (p2
, size
, mtag_mmap_flags
| PROT_READ
| PROT_WRITE
) != 0)
530 __munmap (p2
, HEAP_MAX_SIZE
);
533 h
= (heap_info
*) p2
;
535 h
->mprotect_size
= size
;
536 LIBC_PROBE (memory_heap_new
, 2, h
, h
->size
);
540 /* Grow a heap. size is automatically rounded up to a
541 multiple of the page size. */
544 grow_heap (heap_info
*h
, long diff
)
546 size_t pagesize
= GLRO (dl_pagesize
);
549 diff
= ALIGN_UP (diff
, pagesize
);
550 new_size
= (long) h
->size
+ diff
;
551 if ((unsigned long) new_size
> (unsigned long) HEAP_MAX_SIZE
)
554 if ((unsigned long) new_size
> h
->mprotect_size
)
556 if (__mprotect ((char *) h
+ h
->mprotect_size
,
557 (unsigned long) new_size
- h
->mprotect_size
,
558 mtag_mmap_flags
| PROT_READ
| PROT_WRITE
) != 0)
561 h
->mprotect_size
= new_size
;
565 LIBC_PROBE (memory_heap_more
, 2, h
, h
->size
);
572 shrink_heap (heap_info
*h
, long diff
)
576 new_size
= (long) h
->size
- diff
;
577 if (new_size
< (long) sizeof (*h
))
580 /* Try to re-map the extra heap space freshly to save memory, and make it
581 inaccessible. See malloc-sysdep.h to know when this is true. */
582 if (__glibc_unlikely (check_may_shrink_heap ()))
584 if ((char *) MMAP ((char *) h
+ new_size
, diff
, PROT_NONE
,
585 MAP_FIXED
) == (char *) MAP_FAILED
)
588 h
->mprotect_size
= new_size
;
591 __madvise ((char *) h
+ new_size
, diff
, MADV_DONTNEED
);
592 /*fprintf(stderr, "shrink %p %08lx\n", h, new_size);*/
595 LIBC_PROBE (memory_heap_less
, 2, h
, h
->size
);
601 #define delete_heap(heap) \
603 if ((char *) (heap) + HEAP_MAX_SIZE == aligned_heap_area) \
604 aligned_heap_area = NULL; \
605 __munmap ((char *) (heap), HEAP_MAX_SIZE); \
609 heap_trim (heap_info
*heap
, size_t pad
)
611 mstate ar_ptr
= heap
->ar_ptr
;
612 unsigned long pagesz
= GLRO (dl_pagesize
);
613 mchunkptr top_chunk
= top (ar_ptr
), p
;
614 heap_info
*prev_heap
;
615 long new_size
, top_size
, top_area
, extra
, prev_size
, misalign
;
617 /* Can this heap go away completely? */
618 while (top_chunk
== chunk_at_offset (heap
, sizeof (*heap
)))
620 prev_heap
= heap
->prev
;
621 prev_size
= prev_heap
->size
- (MINSIZE
- 2 * SIZE_SZ
);
622 p
= chunk_at_offset (prev_heap
, prev_size
);
623 /* fencepost must be properly aligned. */
624 misalign
= ((long) p
) & MALLOC_ALIGN_MASK
;
625 p
= chunk_at_offset (prev_heap
, prev_size
- misalign
);
626 assert (chunksize_nomask (p
) == (0 | PREV_INUSE
)); /* must be fencepost */
628 new_size
= chunksize (p
) + (MINSIZE
- 2 * SIZE_SZ
) + misalign
;
629 assert (new_size
> 0 && new_size
< (long) (2 * MINSIZE
));
631 new_size
+= prev_size (p
);
632 assert (new_size
> 0 && new_size
< HEAP_MAX_SIZE
);
633 if (new_size
+ (HEAP_MAX_SIZE
- prev_heap
->size
) < pad
+ MINSIZE
+ pagesz
)
635 ar_ptr
->system_mem
-= heap
->size
;
636 LIBC_PROBE (memory_heap_free
, 2, heap
, heap
->size
);
639 if (!prev_inuse (p
)) /* consolidate backward */
642 unlink_chunk (ar_ptr
, p
);
644 assert (((unsigned long) ((char *) p
+ new_size
) & (pagesz
- 1)) == 0);
645 assert (((char *) p
+ new_size
) == ((char *) heap
+ heap
->size
));
646 top (ar_ptr
) = top_chunk
= p
;
647 set_head (top_chunk
, new_size
| PREV_INUSE
);
648 /*check_chunk(ar_ptr, top_chunk);*/
651 /* Uses similar logic for per-thread arenas as the main arena with systrim
652 and _int_free by preserving the top pad and rounding down to the nearest
654 top_size
= chunksize (top_chunk
);
655 if ((unsigned long)(top_size
) <
656 (unsigned long)(mp_
.trim_threshold
))
659 top_area
= top_size
- MINSIZE
- 1;
660 if (top_area
< 0 || (size_t) top_area
<= pad
)
663 /* Release in pagesize units and round down to the nearest page. */
664 extra
= ALIGN_DOWN(top_area
- pad
, pagesz
);
669 if (shrink_heap (heap
, extra
) != 0)
672 ar_ptr
->system_mem
-= extra
;
674 /* Success. Adjust top accordingly. */
675 set_head (top_chunk
, (top_size
- extra
) | PREV_INUSE
);
676 /*check_chunk(ar_ptr, top_chunk);*/
680 /* Create a new arena with initial size "size". */
682 /* If REPLACED_ARENA is not NULL, detach it from this thread. Must be
683 called while free_list_lock is held. */
685 detach_arena (mstate replaced_arena
)
687 if (replaced_arena
!= NULL
)
689 assert (replaced_arena
->attached_threads
> 0);
690 /* The current implementation only detaches from main_arena in
691 case of allocation failure. This means that it is likely not
692 beneficial to put the arena on free_list even if the
693 reference count reaches zero. */
694 --replaced_arena
->attached_threads
;
699 _int_new_arena (size_t size
)
704 unsigned long misalign
;
706 h
= new_heap (size
+ (sizeof (*h
) + sizeof (*a
) + MALLOC_ALIGNMENT
),
710 /* Maybe size is too large to fit in a single heap. So, just try
711 to create a minimally-sized arena and let _int_malloc() attempt
712 to deal with the large request via mmap_chunk(). */
713 h
= new_heap (sizeof (*h
) + sizeof (*a
) + MALLOC_ALIGNMENT
, mp_
.top_pad
);
717 a
= h
->ar_ptr
= (mstate
) (h
+ 1);
718 malloc_init_state (a
);
719 a
->attached_threads
= 1;
721 a
->system_mem
= a
->max_system_mem
= h
->size
;
723 /* Set up the top chunk, with proper alignment. */
724 ptr
= (char *) (a
+ 1);
725 misalign
= (unsigned long) chunk2mem (ptr
) & MALLOC_ALIGN_MASK
;
727 ptr
+= MALLOC_ALIGNMENT
- misalign
;
728 top (a
) = (mchunkptr
) ptr
;
729 set_head (top (a
), (((char *) h
+ h
->size
) - ptr
) | PREV_INUSE
);
731 LIBC_PROBE (memory_arena_new
, 2, a
, size
);
732 mstate replaced_arena
= thread_arena
;
734 __libc_lock_init (a
->mutex
);
736 __libc_lock_lock (list_lock
);
738 /* Add the new arena to the global list. */
739 a
->next
= main_arena
.next
;
740 /* FIXME: The barrier is an attempt to synchronize with read access
741 in reused_arena, which does not acquire list_lock while
742 traversing the list. */
743 atomic_write_barrier ();
746 __libc_lock_unlock (list_lock
);
748 __libc_lock_lock (free_list_lock
);
749 detach_arena (replaced_arena
);
750 __libc_lock_unlock (free_list_lock
);
752 /* Lock this arena. NB: Another thread may have been attached to
753 this arena because the arena is now accessible from the
754 main_arena.next list and could have been picked by reused_arena.
755 This can only happen for the last arena created (before the arena
756 limit is reached). At this point, some arena has to be attached
757 to two threads. We could acquire the arena lock before list_lock
758 to make it less likely that reused_arena picks this new arena,
759 but this could result in a deadlock with
760 __malloc_fork_lock_parent. */
762 __libc_lock_lock (a
->mutex
);
768 /* Remove an arena from free_list. */
772 mstate replaced_arena
= thread_arena
;
773 mstate result
= free_list
;
776 __libc_lock_lock (free_list_lock
);
780 free_list
= result
->next_free
;
782 /* The arena will be attached to this thread. */
783 assert (result
->attached_threads
== 0);
784 result
->attached_threads
= 1;
786 detach_arena (replaced_arena
);
788 __libc_lock_unlock (free_list_lock
);
792 LIBC_PROBE (memory_arena_reuse_free_list
, 1, result
);
793 __libc_lock_lock (result
->mutex
);
794 thread_arena
= result
;
801 /* Remove the arena from the free list (if it is present).
802 free_list_lock must have been acquired by the caller. */
804 remove_from_free_list (mstate arena
)
806 mstate
*previous
= &free_list
;
807 for (mstate p
= free_list
; p
!= NULL
; p
= p
->next_free
)
809 assert (p
->attached_threads
== 0);
812 /* Remove the requested arena from the list. */
813 *previous
= p
->next_free
;
817 previous
= &p
->next_free
;
821 /* Lock and return an arena that can be reused for memory allocation.
822 Avoid AVOID_ARENA as we have already failed to allocate memory in
823 it and it is currently locked. */
825 reused_arena (mstate avoid_arena
)
828 /* FIXME: Access to next_to_use suffers from data races. */
829 static mstate next_to_use
;
830 if (next_to_use
== NULL
)
831 next_to_use
= &main_arena
;
833 /* Iterate over all arenas (including those linked from
835 result
= next_to_use
;
838 if (!__libc_lock_trylock (result
->mutex
))
841 /* FIXME: This is a data race, see _int_new_arena. */
842 result
= result
->next
;
844 while (result
!= next_to_use
);
846 /* Avoid AVOID_ARENA as we have already failed to allocate memory
847 in that arena and it is currently locked. */
848 if (result
== avoid_arena
)
849 result
= result
->next
;
851 /* No arena available without contention. Wait for the next in line. */
852 LIBC_PROBE (memory_arena_reuse_wait
, 3, &result
->mutex
, result
, avoid_arena
);
853 __libc_lock_lock (result
->mutex
);
856 /* Attach the arena to the current thread. */
858 /* Update the arena thread attachment counters. */
859 mstate replaced_arena
= thread_arena
;
860 __libc_lock_lock (free_list_lock
);
861 detach_arena (replaced_arena
);
863 /* We may have picked up an arena on the free list. We need to
864 preserve the invariant that no arena on the free list has a
865 positive attached_threads counter (otherwise,
866 arena_thread_freeres cannot use the counter to determine if the
867 arena needs to be put on the free list). We unconditionally
868 remove the selected arena from the free list. The caller of
869 reused_arena checked the free list and observed it to be empty,
870 so the list is very short. */
871 remove_from_free_list (result
);
873 ++result
->attached_threads
;
875 __libc_lock_unlock (free_list_lock
);
878 LIBC_PROBE (memory_arena_reuse
, 2, result
, avoid_arena
);
879 thread_arena
= result
;
880 next_to_use
= result
->next
;
886 arena_get2 (size_t size
, mstate avoid_arena
)
890 static size_t narenas_limit
;
892 a
= get_free_list ();
895 /* Nothing immediately available, so generate a new arena. */
896 if (narenas_limit
== 0)
898 if (mp_
.arena_max
!= 0)
899 narenas_limit
= mp_
.arena_max
;
900 else if (narenas
> mp_
.arena_test
)
902 int n
= __get_nprocs ();
905 narenas_limit
= NARENAS_FROM_NCORES (n
);
907 /* We have no information about the system. Assume two
909 narenas_limit
= NARENAS_FROM_NCORES (2);
914 /* NB: the following depends on the fact that (size_t)0 - 1 is a
915 very large number and that the underflow is OK. If arena_max
916 is set the value of arena_test is irrelevant. If arena_test
917 is set but narenas is not yet larger or equal to arena_test
918 narenas_limit is 0. There is no possibility for narenas to
919 be too big for the test to always fail since there is not
920 enough address space to create that many arenas. */
921 if (__glibc_unlikely (n
<= narenas_limit
- 1))
923 if (catomic_compare_and_exchange_bool_acq (&narenas
, n
+ 1, n
))
925 a
= _int_new_arena (size
);
926 if (__glibc_unlikely (a
== NULL
))
927 catomic_decrement (&narenas
);
930 a
= reused_arena (avoid_arena
);
935 /* If we don't have the main arena, then maybe the failure is due to running
936 out of mmapped areas, so we can try allocating on the main arena.
937 Otherwise, it is likely that sbrk() has failed and there is still a chance
938 to mmap(), so try one of the other arenas. */
940 arena_get_retry (mstate ar_ptr
, size_t bytes
)
942 LIBC_PROBE (memory_arena_retry
, 2, bytes
, ar_ptr
);
943 if (ar_ptr
!= &main_arena
)
945 __libc_lock_unlock (ar_ptr
->mutex
);
946 ar_ptr
= &main_arena
;
947 __libc_lock_lock (ar_ptr
->mutex
);
951 __libc_lock_unlock (ar_ptr
->mutex
);
952 ar_ptr
= arena_get2 (bytes
, ar_ptr
);
959 __malloc_arena_thread_freeres (void)
961 /* Shut down the thread cache first. This could deallocate data for
962 the thread arena, so do this before we put the arena on the free
964 tcache_thread_shutdown ();
966 mstate a
= thread_arena
;
971 __libc_lock_lock (free_list_lock
);
972 /* If this was the last attached thread for this arena, put the
973 arena on the free list. */
974 assert (a
->attached_threads
> 0);
975 if (--a
->attached_threads
== 0)
977 a
->next_free
= free_list
;
980 __libc_lock_unlock (free_list_lock
);