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-rw-r--r--deps/mysqllite/mysys/lf_alloc-pin.c527
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diff --git a/deps/mysqllite/mysys/lf_alloc-pin.c b/deps/mysqllite/mysys/lf_alloc-pin.c
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--- a/deps/mysqllite/mysys/lf_alloc-pin.c
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-/* QQ: TODO multi-pinbox */
-/* Copyright (C) 2006-2008 MySQL AB, 2008-2009 Sun Microsystems, Inc.
-
- This program is free software; you can redistribute it and/or modify
- it under the terms of the GNU General Public License as published by
- the Free Software Foundation; version 2 of the License.
-
- This program 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 General Public License for more details.
-
- You should have received a copy of the GNU General Public License
- along with this program; if not, write to the Free Software
- Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
-
-/*
- wait-free concurrent allocator based on pinning addresses
-
- It works as follows: every thread (strictly speaking - every CPU, but
- it's too difficult to do) has a small array of pointers. They're called
- "pins". Before using an object its address must be stored in this array
- (pinned). When an object is no longer necessary its address must be
- removed from this array (unpinned). When a thread wants to free() an
- object it scans all pins of all threads to see if somebody has this
- object pinned. If yes - the object is not freed (but stored in a
- "purgatory"). To reduce the cost of a single free() pins are not scanned
- on every free() but only added to (thread-local) purgatory. On every
- LF_PURGATORY_SIZE free() purgatory is scanned and all unpinned objects
- are freed.
-
- Pins are used to solve ABA problem. To use pins one must obey
- a pinning protocol:
-
- 1. Let's assume that PTR is a shared pointer to an object. Shared means
- that any thread may modify it anytime to point to a different object
- and free the old object. Later the freed object may be potentially
- allocated by another thread. If we're unlucky that other thread may
- set PTR to point to this object again. This is ABA problem.
- 2. Create a local pointer LOCAL_PTR.
- 3. Pin the PTR in a loop:
- do
- {
- LOCAL_PTR= PTR;
- pin(PTR, PIN_NUMBER);
- } while (LOCAL_PTR != PTR)
- 4. It is guaranteed that after the loop has ended, LOCAL_PTR
- points to an object (or NULL, if PTR may be NULL), that
- will never be freed. It is not guaranteed though
- that LOCAL_PTR == PTR (as PTR can change any time)
- 5. When done working with the object, remove the pin:
- unpin(PIN_NUMBER)
- 6. When copying pins (as in the list traversing loop:
- pin(CUR, 1);
- while ()
- {
- do // standard
- { // pinning
- NEXT=CUR->next; // loop
- pin(NEXT, 0); // see #3
- } while (NEXT != CUR->next); // above
- ...
- ...
- CUR=NEXT;
- pin(CUR, 1); // copy pin[0] to pin[1]
- }
- which keeps CUR address constantly pinned), note than pins may be
- copied only upwards (!!!), that is pin[N] to pin[M], M > N.
- 7. Don't keep the object pinned longer than necessary - the number of
- pins you have is limited (and small), keeping an object pinned
- prevents its reuse and cause unnecessary mallocs.
-
- Explanations:
-
- 3. The loop is important. The following can occur:
- thread1> LOCAL_PTR= PTR
- thread2> free(PTR); PTR=0;
- thread1> pin(PTR, PIN_NUMBER);
- now thread1 cannot access LOCAL_PTR, even if it's pinned,
- because it points to a freed memory. That is, it *must*
- verify that it has indeed pinned PTR, the shared pointer.
-
- 6. When a thread wants to free some LOCAL_PTR, and it scans
- all lists of pins to see whether it's pinned, it does it
- upwards, from low pin numbers to high. Thus another thread
- must copy an address from one pin to another in the same
- direction - upwards, otherwise the scanning thread may
- miss it.
-
- Implementation details:
-
- Pins are given away from a "pinbox". Pinbox is stack-based allocator.
- It used dynarray for storing pins, new elements are allocated by dynarray
- as necessary, old are pushed in the stack for reuse. ABA is solved by
- versioning a pointer - because we use an array, a pointer to pins is 16 bit,
- upper 16 bits are used for a version.
-
- It is assumed that pins belong to a THD and are not transferable
- between THD's (LF_PINS::stack_ends_here being a primary reason
- for this limitation).
-*/
-#include <my_global.h>
-#include <my_sys.h>
-#include <lf.h>
-
-#define LF_PINBOX_MAX_PINS 65536
-
-static void _lf_pinbox_real_free(LF_PINS *pins);
-
-/*
- Initialize a pinbox. Normally called from lf_alloc_init.
- See the latter for details.
-*/
-void lf_pinbox_init(LF_PINBOX *pinbox, uint free_ptr_offset,
- lf_pinbox_free_func *free_func, void *free_func_arg)
-{
- DBUG_ASSERT(free_ptr_offset % sizeof(void *) == 0);
- compile_time_assert(sizeof(LF_PINS) == 64);
- lf_dynarray_init(&pinbox->pinarray, sizeof(LF_PINS));
- pinbox->pinstack_top_ver= 0;
- pinbox->pins_in_array= 0;
- pinbox->free_ptr_offset= free_ptr_offset;
- pinbox->free_func= free_func;
- pinbox->free_func_arg= free_func_arg;
-}
-
-void lf_pinbox_destroy(LF_PINBOX *pinbox)
-{
- lf_dynarray_destroy(&pinbox->pinarray);
-}
-
-/*
- Get pins from a pinbox. Usually called via lf_alloc_get_pins() or
- lf_hash_get_pins().
-
- SYNOPSYS
- pinbox -
-
- DESCRIPTION
- get a new LF_PINS structure from a stack of unused pins,
- or allocate a new one out of dynarray.
-
- NOTE
- It is assumed that pins belong to a thread and are not transferable
- between threads.
-*/
-LF_PINS *_lf_pinbox_get_pins(LF_PINBOX *pinbox)
-{
- uint32 pins, next, top_ver;
- LF_PINS *el;
- /*
- We have an array of max. 64k elements.
- The highest index currently allocated is pinbox->pins_in_array.
- Freed elements are in a lifo stack, pinstack_top_ver.
- pinstack_top_ver is 32 bits; 16 low bits are the index in the
- array, to the first element of the list. 16 high bits are a version
- (every time the 16 low bits are updated, the 16 high bits are
- incremented). Versioniong prevents the ABA problem.
- */
- top_ver= pinbox->pinstack_top_ver;
- do
- {
- if (!(pins= top_ver % LF_PINBOX_MAX_PINS))
- {
- /* the stack of free elements is empty */
- pins= my_atomic_add32((int32 volatile*) &pinbox->pins_in_array, 1)+1;
- if (unlikely(pins >= LF_PINBOX_MAX_PINS))
- return 0;
- /*
- note that the first allocated element has index 1 (pins==1).
- index 0 is reserved to mean "NULL pointer"
- */
- el= (LF_PINS *)_lf_dynarray_lvalue(&pinbox->pinarray, pins);
- if (unlikely(!el))
- return 0;
- break;
- }
- el= (LF_PINS *)_lf_dynarray_value(&pinbox->pinarray, pins);
- next= el->link;
- } while (!my_atomic_cas32((int32 volatile*) &pinbox->pinstack_top_ver,
- (int32*) &top_ver,
- top_ver-pins+next+LF_PINBOX_MAX_PINS));
- /*
- set el->link to the index of el in the dynarray (el->link has two usages:
- - if element is allocated, it's its own index
- - if element is free, it's its next element in the free stack
- */
- el->link= pins;
- el->purgatory_count= 0;
- el->pinbox= pinbox;
- el->stack_ends_here= & my_thread_var->stack_ends_here;
- return el;
-}
-
-/*
- Put pins back to a pinbox. Usually called via lf_alloc_put_pins() or
- lf_hash_put_pins().
-
- DESCRIPTION
- empty the purgatory (XXX deadlock warning below!),
- push LF_PINS structure to a stack
-*/
-void _lf_pinbox_put_pins(LF_PINS *pins)
-{
- LF_PINBOX *pinbox= pins->pinbox;
- uint32 top_ver, nr;
- nr= pins->link;
-#ifdef MY_LF_EXTRA_DEBUG
- {
- int i;
- for (i= 0; i < LF_PINBOX_PINS; i++)
- DBUG_ASSERT(pins->pin[i] == 0);
- }
-#endif
- /*
- XXX this will deadlock if other threads will wait for
- the caller to do something after _lf_pinbox_put_pins(),
- and they would have pinned addresses that the caller wants to free.
- Thus: only free pins when all work is done and nobody can wait for you!!!
- */
- while (pins->purgatory_count)
- {
- _lf_pinbox_real_free(pins);
- if (pins->purgatory_count)
- {
- my_atomic_rwlock_wrunlock(&pins->pinbox->pinarray.lock);
- pthread_yield();
- my_atomic_rwlock_wrlock(&pins->pinbox->pinarray.lock);
- }
- }
- top_ver= pinbox->pinstack_top_ver;
- do
- {
- pins->link= top_ver % LF_PINBOX_MAX_PINS;
- } while (!my_atomic_cas32((int32 volatile*) &pinbox->pinstack_top_ver,
- (int32*) &top_ver,
- top_ver-pins->link+nr+LF_PINBOX_MAX_PINS));
- return;
-}
-
-static int ptr_cmp(void **a, void **b)
-{
- return *a < *b ? -1 : *a == *b ? 0 : 1;
-}
-
-#define add_to_purgatory(PINS, ADDR) \
- do \
- { \
- *(void **)((char *)(ADDR)+(PINS)->pinbox->free_ptr_offset)= \
- (PINS)->purgatory; \
- (PINS)->purgatory= (ADDR); \
- (PINS)->purgatory_count++; \
- } while (0)
-
-/*
- Free an object allocated via pinbox allocator
-
- DESCRIPTION
- add an object to purgatory. if necessary, call _lf_pinbox_real_free()
- to actually free something.
-*/
-void _lf_pinbox_free(LF_PINS *pins, void *addr)
-{
- add_to_purgatory(pins, addr);
- if (pins->purgatory_count % LF_PURGATORY_SIZE)
- _lf_pinbox_real_free(pins);
-}
-
-struct st_harvester {
- void **granary;
- int npins;
-};
-
-/*
- callback for _lf_dynarray_iterate:
- scan all pins of all threads and accumulate all pins
-*/
-static int harvest_pins(LF_PINS *el, struct st_harvester *hv)
-{
- int i;
- LF_PINS *el_end= el+min(hv->npins, LF_DYNARRAY_LEVEL_LENGTH);
- for (; el < el_end; el++)
- {
- for (i= 0; i < LF_PINBOX_PINS; i++)
- {
- void *p= el->pin[i];
- if (p)
- *hv->granary++= p;
- }
- }
- /*
- hv->npins may become negative below, but it means that
- we're on the last dynarray page and harvest_pins() won't be
- called again. We don't bother to make hv->npins() correct
- (that is 0) in this case.
- */
- hv->npins-= LF_DYNARRAY_LEVEL_LENGTH;
- return 0;
-}
-
-/*
- callback for _lf_dynarray_iterate:
- scan all pins of all threads and see if addr is present there
-*/
-static int match_pins(LF_PINS *el, void *addr)
-{
- int i;
- LF_PINS *el_end= el+LF_DYNARRAY_LEVEL_LENGTH;
- for (; el < el_end; el++)
- for (i= 0; i < LF_PINBOX_PINS; i++)
- if (el->pin[i] == addr)
- return 1;
- return 0;
-}
-
-#if STACK_DIRECTION < 0
-#define available_stack_size(CUR,END) (long) ((char*)(CUR) - (char*)(END))
-#else
-#define available_stack_size(CUR,END) (long) ((char*)(END) - (char*)(CUR))
-#endif
-
-#define next_node(P, X) (*((uchar * volatile *)(((uchar *)(X)) + (P)->free_ptr_offset)))
-#define anext_node(X) next_node(&allocator->pinbox, (X))
-
-/*
- Scan the purgatory and free everything that can be freed
-*/
-static void _lf_pinbox_real_free(LF_PINS *pins)
-{
- int npins, alloca_size;
- void *list, **addr;
- void *first= NULL, *last= NULL;
- LF_PINBOX *pinbox= pins->pinbox;
-
- npins= pinbox->pins_in_array+1;
-
-#ifdef HAVE_ALLOCA
- alloca_size= sizeof(void *)*LF_PINBOX_PINS*npins;
- /* create a sorted list of pinned addresses, to speed up searches */
- if (available_stack_size(&pinbox, *pins->stack_ends_here) > alloca_size)
- {
- struct st_harvester hv;
- addr= (void **) alloca(alloca_size);
- hv.granary= addr;
- hv.npins= npins;
- /* scan the dynarray and accumulate all pinned addresses */
- _lf_dynarray_iterate(&pinbox->pinarray,
- (lf_dynarray_func)harvest_pins, &hv);
-
- npins= hv.granary-addr;
- /* and sort them */
- if (npins)
- qsort(addr, npins, sizeof(void *), (qsort_cmp)ptr_cmp);
- }
- else
-#endif
- addr= 0;
-
- list= pins->purgatory;
- pins->purgatory= 0;
- pins->purgatory_count= 0;
- while (list)
- {
- void *cur= list;
- list= *(void **)((char *)cur+pinbox->free_ptr_offset);
- if (npins)
- {
- if (addr) /* use binary search */
- {
- void **a, **b, **c;
- for (a= addr, b= addr+npins-1, c= a+(b-a)/2; (b-a) > 1; c= a+(b-a)/2)
- if (cur == *c)
- a= b= c;
- else if (cur > *c)
- a= c;
- else
- b= c;
- if (cur == *a || cur == *b)
- goto found;
- }
- else /* no alloca - no cookie. linear search here */
- {
- if (_lf_dynarray_iterate(&pinbox->pinarray,
- (lf_dynarray_func)match_pins, cur))
- goto found;
- }
- }
- /* not pinned - freeing */
- if (last)
- last= next_node(pinbox, last)= (uchar *)cur;
- else
- first= last= (uchar *)cur;
- continue;
-found:
- /* pinned - keeping */
- add_to_purgatory(pins, cur);
- }
- if (last)
- pinbox->free_func(first, last, pinbox->free_func_arg);
-}
-
-/* lock-free memory allocator for fixed-size objects */
-
-LF_REQUIRE_PINS(1)
-
-/*
- callback for _lf_pinbox_real_free to free a list of unpinned objects -
- add it back to the allocator stack
-
- DESCRIPTION
- 'first' and 'last' are the ends of the linked list of nodes:
- first->el->el->....->el->last. Use first==last to free only one element.
-*/
-static void alloc_free(uchar *first,
- uchar volatile *last,
- LF_ALLOCATOR *allocator)
-{
- /*
- we need a union here to access type-punned pointer reliably.
- otherwise gcc -fstrict-aliasing will not see 'tmp' changed in the loop
- */
- union { uchar * node; void *ptr; } tmp;
- tmp.node= allocator->top;
- do
- {
- anext_node(last)= tmp.node;
- } while (!my_atomic_casptr((void **)(char *)&allocator->top,
- (void **)&tmp.ptr, first) && LF_BACKOFF);
-}
-
-/*
- initialize lock-free allocator
-
- SYNOPSYS
- allocator -
- size a size of an object to allocate
- free_ptr_offset an offset inside the object to a sizeof(void *)
- memory that is guaranteed to be unused after
- the object is put in the purgatory. Unused by ANY
- thread, not only the purgatory owner.
- This memory will be used to link waiting-to-be-freed
- objects in a purgatory list.
-*/
-void lf_alloc_init(LF_ALLOCATOR *allocator, uint size, uint free_ptr_offset)
-{
- lf_pinbox_init(&allocator->pinbox, free_ptr_offset,
- (lf_pinbox_free_func *)alloc_free, allocator);
- allocator->top= 0;
- allocator->mallocs= 0;
- allocator->element_size= size;
- DBUG_ASSERT(size >= sizeof(void*) + free_ptr_offset);
-}
-
-/*
- destroy the allocator, free everything that's in it
-
- NOTE
- As every other init/destroy function here and elsewhere it
- is not thread safe. No, this function is no different, ensure
- that no thread needs the allocator before destroying it.
- We are not responsible for any damage that may be caused by
- accessing the allocator when it is being or has been destroyed.
- Oh yes, and don't put your cat in a microwave.
-*/
-void lf_alloc_destroy(LF_ALLOCATOR *allocator)
-{
- uchar *node= allocator->top;
- while (node)
- {
- uchar *tmp= anext_node(node);
- my_free(node);
- node= tmp;
- }
- lf_pinbox_destroy(&allocator->pinbox);
- allocator->top= 0;
-}
-
-/*
- Allocate and return an new object.
-
- DESCRIPTION
- Pop an unused object from the stack or malloc it is the stack is empty.
- pin[0] is used, it's removed on return.
-*/
-void *_lf_alloc_new(LF_PINS *pins)
-{
- LF_ALLOCATOR *allocator= (LF_ALLOCATOR *)(pins->pinbox->free_func_arg);
- uchar *node;
- for (;;)
- {
- do
- {
- node= allocator->top;
- _lf_pin(pins, 0, node);
- } while (node != allocator->top && LF_BACKOFF);
- if (!node)
- {
- node= (void *)my_malloc(allocator->element_size, MYF(MY_WME));
-#ifdef MY_LF_EXTRA_DEBUG
- if (likely(node != 0))
- my_atomic_add32(&allocator->mallocs, 1);
-#endif
- break;
- }
- if (my_atomic_casptr((void **)(char *)&allocator->top,
- (void *)&node, anext_node(node)))
- break;
- }
- _lf_unpin(pins, 0);
- return node;
-}
-
-/*
- count the number of objects in a pool.
-
- NOTE
- This is NOT thread-safe !!!
-*/
-uint lf_alloc_pool_count(LF_ALLOCATOR *allocator)
-{
- uint i;
- uchar *node;
- for (node= allocator->top, i= 0; node; node= anext_node(node), i++)
- /* no op */;
- return i;
-}
-