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.
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public License as
7 published by the Free Software Foundation; either version 2.1 of the
8 License, or (at your option) any later version.
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; see the file COPYING.LIB. If
17 not, see <https://www.gnu.org/licenses/>. */
22 # define TUNABLE_NAMESPACE malloc
24 #include <elf/dl-tunables.h>
26 /* Compile-time constants. */
28 #define HEAP_MIN_SIZE (32 * 1024)
30 # ifdef DEFAULT_MMAP_THRESHOLD_MAX
31 # define HEAP_MAX_SIZE (2 * DEFAULT_MMAP_THRESHOLD_MAX)
33 # define HEAP_MAX_SIZE (1024 * 1024) /* must be a power of two */
37 /* HEAP_MIN_SIZE and HEAP_MAX_SIZE limit the size of mmap()ed heaps
38 that are dynamically created for multi-threaded programs. The
39 maximum size must be a power of two, for fast determination of
40 which heap belongs to a chunk. It should be much larger than the
41 mmap threshold, so that requests with a size just below that
42 threshold can be fulfilled without creating too many heaps. */
44 /***************************************************************************/
46 #define top(ar_ptr) ((ar_ptr)->top)
48 /* A heap is a single contiguous memory region holding (coalesceable)
49 malloc_chunks. It is allocated with mmap() and always starts at an
50 address aligned to HEAP_MAX_SIZE. */
52 typedef struct _heap_info
54 mstate ar_ptr
; /* Arena for this heap. */
55 struct _heap_info
*prev
; /* Previous heap. */
56 size_t size
; /* Current size in bytes. */
57 size_t mprotect_size
; /* Size in bytes that has been mprotected
58 PROT_READ|PROT_WRITE. */
59 /* Make sure the following data is properly aligned, particularly
60 that sizeof (heap_info) + 2 * SIZE_SZ is a multiple of
62 char pad
[-6 * SIZE_SZ
& MALLOC_ALIGN_MASK
];
65 /* Get a compile-time error if the heap_info padding is not correct
66 to make alignment work as expected in sYSMALLOc. */
67 extern int sanity_check_heap_info_alignment
[(sizeof (heap_info
)
68 + 2 * SIZE_SZ
) % MALLOC_ALIGNMENT
71 /* Thread specific data. */
73 static __thread mstate thread_arena attribute_tls_model_ie
;
75 /* Arena free list. free_list_lock synchronizes access to the
76 free_list variable below, and the next_free and attached_threads
77 members of struct malloc_state objects. No other locks must be
78 acquired after free_list_lock has been acquired. */
80 __libc_lock_define_initialized (static, free_list_lock
);
82 static size_t narenas
= 1;
84 static mstate free_list
;
86 /* list_lock prevents concurrent writes to the next member of struct
89 Read access to the next member is supposed to synchronize with the
90 atomic_write_barrier and the write to the next member in
91 _int_new_arena. This suffers from data races; see the FIXME
92 comments in _int_new_arena and reused_arena.
94 list_lock also prevents concurrent forks. At the time list_lock is
95 acquired, no arena lock must have been acquired, but it is
96 permitted to acquire arena locks subsequently, while list_lock is
98 __libc_lock_define_initialized (static, list_lock
);
100 /* Already initialized? */
101 static bool __malloc_initialized
= false;
103 /**************************************************************************/
106 /* arena_get() acquires an arena and locks the corresponding mutex.
107 First, try the one last locked successfully by this thread. (This
108 is the common case and handled with a macro for speed.) Then, loop
109 once over the circularly linked list of arenas. If no arena is
110 readily available, create a new one. In this latter case, `size'
111 is just a hint as to how much memory will be required immediately
114 #define arena_get(ptr, size) do { \
115 ptr = thread_arena; \
116 arena_lock (ptr, size); \
119 #define arena_lock(ptr, size) do { \
121 __libc_lock_lock (ptr->mutex); \
123 ptr = arena_get2 ((size), NULL); \
126 /* find the heap and corresponding arena for a given ptr */
128 #define heap_for_ptr(ptr) \
129 ((heap_info *) ((unsigned long) (ptr) & ~(HEAP_MAX_SIZE - 1)))
130 #define arena_for_chunk(ptr) \
131 (chunk_main_arena (ptr) ? &main_arena : heap_for_ptr (ptr)->ar_ptr)
134 /**************************************************************************/
136 /* atfork support. */
138 /* The following three functions are called around fork from a
139 multi-threaded process. We do not use the general fork handler
140 mechanism to make sure that our handlers are the last ones being
141 called, so that other fork handlers can use the malloc
145 __malloc_fork_lock_parent (void)
147 if (!__malloc_initialized
)
150 /* We do not acquire free_list_lock here because we completely
151 reconstruct free_list in __malloc_fork_unlock_child. */
153 __libc_lock_lock (list_lock
);
155 for (mstate ar_ptr
= &main_arena
;; )
157 __libc_lock_lock (ar_ptr
->mutex
);
158 ar_ptr
= ar_ptr
->next
;
159 if (ar_ptr
== &main_arena
)
165 __malloc_fork_unlock_parent (void)
167 if (!__malloc_initialized
)
170 for (mstate ar_ptr
= &main_arena
;; )
172 __libc_lock_unlock (ar_ptr
->mutex
);
173 ar_ptr
= ar_ptr
->next
;
174 if (ar_ptr
== &main_arena
)
177 __libc_lock_unlock (list_lock
);
181 __malloc_fork_unlock_child (void)
183 if (!__malloc_initialized
)
186 /* Push all arenas to the free list, except thread_arena, which is
187 attached to the current thread. */
188 __libc_lock_init (free_list_lock
);
189 if (thread_arena
!= NULL
)
190 thread_arena
->attached_threads
= 1;
192 for (mstate ar_ptr
= &main_arena
;; )
194 __libc_lock_init (ar_ptr
->mutex
);
195 if (ar_ptr
!= thread_arena
)
197 /* This arena is no longer attached to any thread. */
198 ar_ptr
->attached_threads
= 0;
199 ar_ptr
->next_free
= free_list
;
202 ar_ptr
= ar_ptr
->next
;
203 if (ar_ptr
== &main_arena
)
207 __libc_lock_init (list_lock
);
211 # define TUNABLE_CALLBACK_FNDECL(__name, __type) \
212 static inline int do_ ## __name (__type value); \
214 TUNABLE_CALLBACK (__name) (tunable_val_t *valp) \
216 __type value = (__type) (valp)->numval; \
217 do_ ## __name (value); \
220 TUNABLE_CALLBACK_FNDECL (set_mmap_threshold
, size_t)
221 TUNABLE_CALLBACK_FNDECL (set_mmaps_max
, int32_t)
222 TUNABLE_CALLBACK_FNDECL (set_top_pad
, size_t)
223 TUNABLE_CALLBACK_FNDECL (set_perturb_byte
, int32_t)
224 TUNABLE_CALLBACK_FNDECL (set_trim_threshold
, size_t)
225 TUNABLE_CALLBACK_FNDECL (set_arena_max
, size_t)
226 TUNABLE_CALLBACK_FNDECL (set_arena_test
, size_t)
228 TUNABLE_CALLBACK_FNDECL (set_tcache_max
, size_t)
229 TUNABLE_CALLBACK_FNDECL (set_tcache_count
, size_t)
230 TUNABLE_CALLBACK_FNDECL (set_tcache_unsorted_limit
, size_t)
232 TUNABLE_CALLBACK_FNDECL (set_mxfast
, size_t)
234 /* Initialization routine. */
236 extern char **_environ
;
239 next_env_entry (char ***position
)
241 char **current
= *position
;
244 while (*current
!= NULL
)
246 if (__builtin_expect ((*current
)[0] == 'M', 0)
247 && (*current
)[1] == 'A'
248 && (*current
)[2] == 'L'
249 && (*current
)[3] == 'L'
250 && (*current
)[4] == 'O'
251 && (*current
)[5] == 'C'
252 && (*current
)[6] == '_')
254 result
= &(*current
)[7];
256 /* Save current position for next visit. */
257 *position
= ++current
;
271 extern struct dl_open_hook
*_dl_open_hook
;
272 libc_hidden_proto (_dl_open_hook
);
276 static void tcache_key_initialize (void);
282 if (__malloc_initialized
)
285 __malloc_initialized
= true;
288 tcache_key_initialize ();
292 if ((TUNABLE_GET_FULL (glibc
, mem
, tagging
, int32_t, NULL
) & 1) != 0)
294 /* If the tunable says that we should be using tagged memory
295 and that morecore does not support tagged regions, then
297 if (__MTAG_SBRK_UNTAGGED
)
298 __always_fail_morecore
= true;
301 mtag_mmap_flags
= __MTAG_MMAP_FLAGS
;
305 #if defined SHARED && IS_IN (libc)
306 /* In case this libc copy is in a non-default namespace, never use
307 brk. Likewise if dlopened from statically linked program. The
308 generic sbrk implementation also enforces this, but it is not
311 __always_fail_morecore
= true;
314 thread_arena
= &main_arena
;
316 malloc_init_state (&main_arena
);
319 TUNABLE_GET (top_pad
, size_t, TUNABLE_CALLBACK (set_top_pad
));
320 TUNABLE_GET (perturb
, int32_t, TUNABLE_CALLBACK (set_perturb_byte
));
321 TUNABLE_GET (mmap_threshold
, size_t, TUNABLE_CALLBACK (set_mmap_threshold
));
322 TUNABLE_GET (trim_threshold
, size_t, TUNABLE_CALLBACK (set_trim_threshold
));
323 TUNABLE_GET (mmap_max
, int32_t, TUNABLE_CALLBACK (set_mmaps_max
));
324 TUNABLE_GET (arena_max
, size_t, TUNABLE_CALLBACK (set_arena_max
));
325 TUNABLE_GET (arena_test
, size_t, TUNABLE_CALLBACK (set_arena_test
));
327 TUNABLE_GET (tcache_max
, size_t, TUNABLE_CALLBACK (set_tcache_max
));
328 TUNABLE_GET (tcache_count
, size_t, TUNABLE_CALLBACK (set_tcache_count
));
329 TUNABLE_GET (tcache_unsorted_limit
, size_t,
330 TUNABLE_CALLBACK (set_tcache_unsorted_limit
));
332 TUNABLE_GET (mxfast
, size_t, TUNABLE_CALLBACK (set_mxfast
));
334 if (__glibc_likely (_environ
!= NULL
))
336 char **runp
= _environ
;
339 while (__builtin_expect ((envline
= next_env_entry (&runp
)) != NULL
,
342 size_t len
= strcspn (envline
, "=");
344 if (envline
[len
] != '=')
345 /* This is a "MALLOC_" variable at the end of the string
346 without a '=' character. Ignore it since otherwise we
347 will access invalid memory below. */
353 if (!__builtin_expect (__libc_enable_secure
, 0))
355 if (memcmp (envline
, "TOP_PAD_", 8) == 0)
356 __libc_mallopt (M_TOP_PAD
, atoi (&envline
[9]));
357 else if (memcmp (envline
, "PERTURB_", 8) == 0)
358 __libc_mallopt (M_PERTURB
, atoi (&envline
[9]));
362 if (!__builtin_expect (__libc_enable_secure
, 0))
364 if (memcmp (envline
, "MMAP_MAX_", 9) == 0)
365 __libc_mallopt (M_MMAP_MAX
, atoi (&envline
[10]));
366 else if (memcmp (envline
, "ARENA_MAX", 9) == 0)
367 __libc_mallopt (M_ARENA_MAX
, atoi (&envline
[10]));
371 if (!__builtin_expect (__libc_enable_secure
, 0))
373 if (memcmp (envline
, "ARENA_TEST", 10) == 0)
374 __libc_mallopt (M_ARENA_TEST
, atoi (&envline
[11]));
378 if (!__builtin_expect (__libc_enable_secure
, 0))
380 if (memcmp (envline
, "TRIM_THRESHOLD_", 15) == 0)
381 __libc_mallopt (M_TRIM_THRESHOLD
, atoi (&envline
[16]));
382 else if (memcmp (envline
, "MMAP_THRESHOLD_", 15) == 0)
383 __libc_mallopt (M_MMAP_THRESHOLD
, atoi (&envline
[16]));
394 /* Managing heaps and arenas (for concurrent threads) */
398 /* Print the complete contents of a single heap to stderr. */
401 dump_heap (heap_info
*heap
)
406 fprintf (stderr
, "Heap %p, size %10lx:\n", heap
, (long) heap
->size
);
407 ptr
= (heap
->ar_ptr
!= (mstate
) (heap
+ 1)) ?
408 (char *) (heap
+ 1) : (char *) (heap
+ 1) + sizeof (struct malloc_state
);
409 p
= (mchunkptr
) (((unsigned long) ptr
+ MALLOC_ALIGN_MASK
) &
413 fprintf (stderr
, "chunk %p size %10lx", p
, (long) chunksize_nomask(p
));
414 if (p
== top (heap
->ar_ptr
))
416 fprintf (stderr
, " (top)\n");
419 else if (chunksize_nomask(p
) == (0 | PREV_INUSE
))
421 fprintf (stderr
, " (fence)\n");
424 fprintf (stderr
, "\n");
428 #endif /* MALLOC_DEBUG > 1 */
430 /* If consecutive mmap (0, HEAP_MAX_SIZE << 1, ...) calls return decreasing
431 addresses as opposed to increasing, new_heap would badly fragment the
432 address space. In that case remember the second HEAP_MAX_SIZE part
433 aligned to HEAP_MAX_SIZE from last mmap (0, HEAP_MAX_SIZE << 1, ...)
434 call (if it is already aligned) and try to reuse it next time. We need
435 no locking for it, as kernel ensures the atomicity for us - worst case
436 we'll call mmap (addr, HEAP_MAX_SIZE, ...) for some value of addr in
437 multiple threads, but only one will succeed. */
438 static char *aligned_heap_area
;
440 /* Create a new heap. size is automatically rounded up to a multiple
444 new_heap (size_t size
, size_t top_pad
)
446 size_t pagesize
= GLRO (dl_pagesize
);
451 if (size
+ top_pad
< HEAP_MIN_SIZE
)
452 size
= HEAP_MIN_SIZE
;
453 else if (size
+ top_pad
<= HEAP_MAX_SIZE
)
455 else if (size
> HEAP_MAX_SIZE
)
458 size
= HEAP_MAX_SIZE
;
459 size
= ALIGN_UP (size
, pagesize
);
461 /* A memory region aligned to a multiple of HEAP_MAX_SIZE is needed.
462 No swap space needs to be reserved for the following large
463 mapping (on Linux, this is the case for all non-writable mappings
466 if (aligned_heap_area
)
468 p2
= (char *) MMAP (aligned_heap_area
, HEAP_MAX_SIZE
, PROT_NONE
,
470 aligned_heap_area
= NULL
;
471 if (p2
!= MAP_FAILED
&& ((unsigned long) p2
& (HEAP_MAX_SIZE
- 1)))
473 __munmap (p2
, HEAP_MAX_SIZE
);
477 if (p2
== MAP_FAILED
)
479 p1
= (char *) MMAP (0, HEAP_MAX_SIZE
<< 1, PROT_NONE
, MAP_NORESERVE
);
480 if (p1
!= MAP_FAILED
)
482 p2
= (char *) (((unsigned long) p1
+ (HEAP_MAX_SIZE
- 1))
483 & ~(HEAP_MAX_SIZE
- 1));
488 aligned_heap_area
= p2
+ HEAP_MAX_SIZE
;
489 __munmap (p2
+ HEAP_MAX_SIZE
, HEAP_MAX_SIZE
- ul
);
493 /* Try to take the chance that an allocation of only HEAP_MAX_SIZE
494 is already aligned. */
495 p2
= (char *) MMAP (0, HEAP_MAX_SIZE
, PROT_NONE
, MAP_NORESERVE
);
496 if (p2
== MAP_FAILED
)
499 if ((unsigned long) p2
& (HEAP_MAX_SIZE
- 1))
501 __munmap (p2
, HEAP_MAX_SIZE
);
506 if (__mprotect (p2
, size
, mtag_mmap_flags
| PROT_READ
| PROT_WRITE
) != 0)
508 __munmap (p2
, HEAP_MAX_SIZE
);
511 h
= (heap_info
*) p2
;
513 h
->mprotect_size
= size
;
514 LIBC_PROBE (memory_heap_new
, 2, h
, h
->size
);
518 /* Grow a heap. size is automatically rounded up to a
519 multiple of the page size. */
522 grow_heap (heap_info
*h
, long diff
)
524 size_t pagesize
= GLRO (dl_pagesize
);
527 diff
= ALIGN_UP (diff
, pagesize
);
528 new_size
= (long) h
->size
+ diff
;
529 if ((unsigned long) new_size
> (unsigned long) HEAP_MAX_SIZE
)
532 if ((unsigned long) new_size
> h
->mprotect_size
)
534 if (__mprotect ((char *) h
+ h
->mprotect_size
,
535 (unsigned long) new_size
- h
->mprotect_size
,
536 mtag_mmap_flags
| PROT_READ
| PROT_WRITE
) != 0)
539 h
->mprotect_size
= new_size
;
543 LIBC_PROBE (memory_heap_more
, 2, h
, h
->size
);
550 shrink_heap (heap_info
*h
, long diff
)
554 new_size
= (long) h
->size
- diff
;
555 if (new_size
< (long) sizeof (*h
))
558 /* Try to re-map the extra heap space freshly to save memory, and make it
559 inaccessible. See malloc-sysdep.h to know when this is true. */
560 if (__glibc_unlikely (check_may_shrink_heap ()))
562 if ((char *) MMAP ((char *) h
+ new_size
, diff
, PROT_NONE
,
563 MAP_FIXED
) == (char *) MAP_FAILED
)
566 h
->mprotect_size
= new_size
;
569 __madvise ((char *) h
+ new_size
, diff
, MADV_DONTNEED
);
570 /*fprintf(stderr, "shrink %p %08lx\n", h, new_size);*/
573 LIBC_PROBE (memory_heap_less
, 2, h
, h
->size
);
579 #define delete_heap(heap) \
581 if ((char *) (heap) + HEAP_MAX_SIZE == aligned_heap_area) \
582 aligned_heap_area = NULL; \
583 __munmap ((char *) (heap), HEAP_MAX_SIZE); \
587 heap_trim (heap_info
*heap
, size_t pad
)
589 mstate ar_ptr
= heap
->ar_ptr
;
590 unsigned long pagesz
= GLRO (dl_pagesize
);
591 mchunkptr top_chunk
= top (ar_ptr
), p
;
592 heap_info
*prev_heap
;
593 long new_size
, top_size
, top_area
, extra
, prev_size
, misalign
;
595 /* Can this heap go away completely? */
596 while (top_chunk
== chunk_at_offset (heap
, sizeof (*heap
)))
598 prev_heap
= heap
->prev
;
599 prev_size
= prev_heap
->size
- (MINSIZE
- 2 * SIZE_SZ
);
600 p
= chunk_at_offset (prev_heap
, prev_size
);
601 /* fencepost must be properly aligned. */
602 misalign
= ((long) p
) & MALLOC_ALIGN_MASK
;
603 p
= chunk_at_offset (prev_heap
, prev_size
- misalign
);
604 assert (chunksize_nomask (p
) == (0 | PREV_INUSE
)); /* must be fencepost */
606 new_size
= chunksize (p
) + (MINSIZE
- 2 * SIZE_SZ
) + misalign
;
607 assert (new_size
> 0 && new_size
< (long) (2 * MINSIZE
));
609 new_size
+= prev_size (p
);
610 assert (new_size
> 0 && new_size
< HEAP_MAX_SIZE
);
611 if (new_size
+ (HEAP_MAX_SIZE
- prev_heap
->size
) < pad
+ MINSIZE
+ pagesz
)
613 ar_ptr
->system_mem
-= heap
->size
;
614 LIBC_PROBE (memory_heap_free
, 2, heap
, heap
->size
);
617 if (!prev_inuse (p
)) /* consolidate backward */
620 unlink_chunk (ar_ptr
, p
);
622 assert (((unsigned long) ((char *) p
+ new_size
) & (pagesz
- 1)) == 0);
623 assert (((char *) p
+ new_size
) == ((char *) heap
+ heap
->size
));
624 top (ar_ptr
) = top_chunk
= p
;
625 set_head (top_chunk
, new_size
| PREV_INUSE
);
626 /*check_chunk(ar_ptr, top_chunk);*/
629 /* Uses similar logic for per-thread arenas as the main arena with systrim
630 and _int_free by preserving the top pad and rounding down to the nearest
632 top_size
= chunksize (top_chunk
);
633 if ((unsigned long)(top_size
) <
634 (unsigned long)(mp_
.trim_threshold
))
637 top_area
= top_size
- MINSIZE
- 1;
638 if (top_area
< 0 || (size_t) top_area
<= pad
)
641 /* Release in pagesize units and round down to the nearest page. */
642 extra
= ALIGN_DOWN(top_area
- pad
, pagesz
);
647 if (shrink_heap (heap
, extra
) != 0)
650 ar_ptr
->system_mem
-= extra
;
652 /* Success. Adjust top accordingly. */
653 set_head (top_chunk
, (top_size
- extra
) | PREV_INUSE
);
654 /*check_chunk(ar_ptr, top_chunk);*/
658 /* Create a new arena with initial size "size". */
661 /* If REPLACED_ARENA is not NULL, detach it from this thread. Must be
662 called while free_list_lock is held. */
664 detach_arena (mstate replaced_arena
)
666 if (replaced_arena
!= NULL
)
668 assert (replaced_arena
->attached_threads
> 0);
669 /* The current implementation only detaches from main_arena in
670 case of allocation failure. This means that it is likely not
671 beneficial to put the arena on free_list even if the
672 reference count reaches zero. */
673 --replaced_arena
->attached_threads
;
678 _int_new_arena (size_t size
)
683 unsigned long misalign
;
685 h
= new_heap (size
+ (sizeof (*h
) + sizeof (*a
) + MALLOC_ALIGNMENT
),
689 /* Maybe size is too large to fit in a single heap. So, just try
690 to create a minimally-sized arena and let _int_malloc() attempt
691 to deal with the large request via mmap_chunk(). */
692 h
= new_heap (sizeof (*h
) + sizeof (*a
) + MALLOC_ALIGNMENT
, mp_
.top_pad
);
696 a
= h
->ar_ptr
= (mstate
) (h
+ 1);
697 malloc_init_state (a
);
698 a
->attached_threads
= 1;
700 a
->system_mem
= a
->max_system_mem
= h
->size
;
702 /* Set up the top chunk, with proper alignment. */
703 ptr
= (char *) (a
+ 1);
704 misalign
= (unsigned long) chunk2mem (ptr
) & MALLOC_ALIGN_MASK
;
706 ptr
+= MALLOC_ALIGNMENT
- misalign
;
707 top (a
) = (mchunkptr
) ptr
;
708 set_head (top (a
), (((char *) h
+ h
->size
) - ptr
) | PREV_INUSE
);
710 LIBC_PROBE (memory_arena_new
, 2, a
, size
);
711 mstate replaced_arena
= thread_arena
;
713 __libc_lock_init (a
->mutex
);
715 __libc_lock_lock (list_lock
);
717 /* Add the new arena to the global list. */
718 a
->next
= main_arena
.next
;
719 /* FIXME: The barrier is an attempt to synchronize with read access
720 in reused_arena, which does not acquire list_lock while
721 traversing the list. */
722 atomic_write_barrier ();
725 __libc_lock_unlock (list_lock
);
727 __libc_lock_lock (free_list_lock
);
728 detach_arena (replaced_arena
);
729 __libc_lock_unlock (free_list_lock
);
731 /* Lock this arena. NB: Another thread may have been attached to
732 this arena because the arena is now accessible from the
733 main_arena.next list and could have been picked by reused_arena.
734 This can only happen for the last arena created (before the arena
735 limit is reached). At this point, some arena has to be attached
736 to two threads. We could acquire the arena lock before list_lock
737 to make it less likely that reused_arena picks this new arena,
738 but this could result in a deadlock with
739 __malloc_fork_lock_parent. */
741 __libc_lock_lock (a
->mutex
);
747 /* Remove an arena from free_list. */
751 mstate replaced_arena
= thread_arena
;
752 mstate result
= free_list
;
755 __libc_lock_lock (free_list_lock
);
759 free_list
= result
->next_free
;
761 /* The arena will be attached to this thread. */
762 assert (result
->attached_threads
== 0);
763 result
->attached_threads
= 1;
765 detach_arena (replaced_arena
);
767 __libc_lock_unlock (free_list_lock
);
771 LIBC_PROBE (memory_arena_reuse_free_list
, 1, result
);
772 __libc_lock_lock (result
->mutex
);
773 thread_arena
= result
;
780 /* Remove the arena from the free list (if it is present).
781 free_list_lock must have been acquired by the caller. */
783 remove_from_free_list (mstate arena
)
785 mstate
*previous
= &free_list
;
786 for (mstate p
= free_list
; p
!= NULL
; p
= p
->next_free
)
788 assert (p
->attached_threads
== 0);
791 /* Remove the requested arena from the list. */
792 *previous
= p
->next_free
;
796 previous
= &p
->next_free
;
800 /* Lock and return an arena that can be reused for memory allocation.
801 Avoid AVOID_ARENA as we have already failed to allocate memory in
802 it and it is currently locked. */
804 reused_arena (mstate avoid_arena
)
807 /* FIXME: Access to next_to_use suffers from data races. */
808 static mstate next_to_use
;
809 if (next_to_use
== NULL
)
810 next_to_use
= &main_arena
;
812 /* Iterate over all arenas (including those linked from
814 result
= next_to_use
;
817 if (!__libc_lock_trylock (result
->mutex
))
820 /* FIXME: This is a data race, see _int_new_arena. */
821 result
= result
->next
;
823 while (result
!= next_to_use
);
825 /* Avoid AVOID_ARENA as we have already failed to allocate memory
826 in that arena and it is currently locked. */
827 if (result
== avoid_arena
)
828 result
= result
->next
;
830 /* No arena available without contention. Wait for the next in line. */
831 LIBC_PROBE (memory_arena_reuse_wait
, 3, &result
->mutex
, result
, avoid_arena
);
832 __libc_lock_lock (result
->mutex
);
835 /* Attach the arena to the current thread. */
837 /* Update the arena thread attachment counters. */
838 mstate replaced_arena
= thread_arena
;
839 __libc_lock_lock (free_list_lock
);
840 detach_arena (replaced_arena
);
842 /* We may have picked up an arena on the free list. We need to
843 preserve the invariant that no arena on the free list has a
844 positive attached_threads counter (otherwise,
845 arena_thread_freeres cannot use the counter to determine if the
846 arena needs to be put on the free list). We unconditionally
847 remove the selected arena from the free list. The caller of
848 reused_arena checked the free list and observed it to be empty,
849 so the list is very short. */
850 remove_from_free_list (result
);
852 ++result
->attached_threads
;
854 __libc_lock_unlock (free_list_lock
);
857 LIBC_PROBE (memory_arena_reuse
, 2, result
, avoid_arena
);
858 thread_arena
= result
;
859 next_to_use
= result
->next
;
865 arena_get2 (size_t size
, mstate avoid_arena
)
869 static size_t narenas_limit
;
871 a
= get_free_list ();
874 /* Nothing immediately available, so generate a new arena. */
875 if (narenas_limit
== 0)
877 if (mp_
.arena_max
!= 0)
878 narenas_limit
= mp_
.arena_max
;
879 else if (narenas
> mp_
.arena_test
)
881 int n
= __get_nprocs_sched ();
884 narenas_limit
= NARENAS_FROM_NCORES (n
);
886 /* We have no information about the system. Assume two
888 narenas_limit
= NARENAS_FROM_NCORES (2);
893 /* NB: the following depends on the fact that (size_t)0 - 1 is a
894 very large number and that the underflow is OK. If arena_max
895 is set the value of arena_test is irrelevant. If arena_test
896 is set but narenas is not yet larger or equal to arena_test
897 narenas_limit is 0. There is no possibility for narenas to
898 be too big for the test to always fail since there is not
899 enough address space to create that many arenas. */
900 if (__glibc_unlikely (n
<= narenas_limit
- 1))
902 if (catomic_compare_and_exchange_bool_acq (&narenas
, n
+ 1, n
))
904 a
= _int_new_arena (size
);
905 if (__glibc_unlikely (a
== NULL
))
906 catomic_decrement (&narenas
);
909 a
= reused_arena (avoid_arena
);
914 /* If we don't have the main arena, then maybe the failure is due to running
915 out of mmapped areas, so we can try allocating on the main arena.
916 Otherwise, it is likely that sbrk() has failed and there is still a chance
917 to mmap(), so try one of the other arenas. */
919 arena_get_retry (mstate ar_ptr
, size_t bytes
)
921 LIBC_PROBE (memory_arena_retry
, 2, bytes
, ar_ptr
);
922 if (ar_ptr
!= &main_arena
)
924 __libc_lock_unlock (ar_ptr
->mutex
);
925 ar_ptr
= &main_arena
;
926 __libc_lock_lock (ar_ptr
->mutex
);
930 __libc_lock_unlock (ar_ptr
->mutex
);
931 ar_ptr
= arena_get2 (bytes
, ar_ptr
);
939 __malloc_arena_thread_freeres (void)
941 /* Shut down the thread cache first. This could deallocate data for
942 the thread arena, so do this before we put the arena on the free
944 tcache_thread_shutdown ();
946 mstate a
= thread_arena
;
951 __libc_lock_lock (free_list_lock
);
952 /* If this was the last attached thread for this arena, put the
953 arena on the free list. */
954 assert (a
->attached_threads
> 0);
955 if (--a
->attached_threads
== 0)
957 a
->next_free
= free_list
;
960 __libc_lock_unlock (free_list_lock
);