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atomlist.h
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// SPDX-License-Identifier: ISC
/*
* Copyright (c) 2016-2019 David Lamparter, for NetDEF, Inc.
*/
#ifndef _FRR_ATOMLIST_H
#define _FRR_ATOMLIST_H
#include "typesafe.h"
#include "frratomic.h"
#ifdef __cplusplus
extern "C" {
#endif
/* pointer with lock/deleted/invalid bit in lowest bit
*
* for atomlist/atomsort, "locked" means "this pointer can't be updated, the
* item is being deleted". it is permissible to assume the item will indeed
* be deleted (as there are no replace/etc. ops in this).
*
* in general, lowest 2/3 bits on 32/64bit architectures are available for
* uses like this; the only thing that will really break this is putting an
* atomlist_item in a struct with "packed" attribute. (it'll break
* immediately and consistently.) -- don't do that.
*
* ATOMPTR_USER is currently unused (and available for atomic hash or skiplist
* implementations.)
*/
/* atomic_atomptr_t may look a bit odd, it's for the sake of C++ compat */
typedef uintptr_t atomptr_t;
typedef atomic_uintptr_t atomic_atomptr_t;
#define ATOMPTR_MASK (UINTPTR_MAX - 3)
#define ATOMPTR_LOCK (1)
#define ATOMPTR_USER (2)
#define ATOMPTR_NULL (0)
static inline atomptr_t atomptr_i(void *val)
{
atomptr_t atomval = (atomptr_t)val;
assert(!(atomval & ATOMPTR_LOCK));
return atomval;
}
static inline void *atomptr_p(atomptr_t val)
{
return (void *)(val & ATOMPTR_MASK);
}
static inline bool atomptr_l(atomptr_t val)
{
return (bool)(val & ATOMPTR_LOCK);
}
static inline bool atomptr_u(atomptr_t val)
{
return (bool)(val & ATOMPTR_USER);
}
/* the problem with, find(), find_gteq() and find_lt() on atomic lists is that
* they're neither an "acquire" nor a "release" operation; the element that
* was found is still on the list and doesn't change ownership. Therefore,
* an atomic transition in ownership state can't be implemented.
*
* Contrast this with add() or pop(): both function calls atomically transfer
* ownership of an item to or from the list, which makes them "acquire" /
* "release" operations.
*
* What can be implemented atomically is a "find_pop()", i.e. try to locate an
* item and atomically try to remove it if found. It's not currently
* implemented but can be added when needed.
*
* Either way - for find(), generally speaking, if you need to use find() on
* a list then the whole thing probably isn't well-suited to atomic
* implementation and you'll need to have extra locks around to make it work
* correctly.
*/
#ifdef WNO_ATOMLIST_UNSAFE_FIND
# define atomic_find_warn
#else
# define atomic_find_warn __attribute__((_DEPRECATED( \
"WARNING: find() on atomic lists cannot be atomic by principle; " \
"check code to make sure usage pattern is OK and if it is, use " \
"#define WNO_ATOMLIST_UNSAFE_FIND")))
#endif
/* single-linked list, unsorted/arbitrary.
* can be used as queue with add_tail / pop
*
* all operations are lock-free, but not necessarily wait-free. this means
* that there is no state where the system as a whole stops making process,
* but it *is* possible that a *particular* thread is delayed by some time.
*
* the only way for this to happen is for other threads to continuously make
* updates. an inactive / blocked / deadlocked other thread cannot cause such
* delays, and to cause such delays a thread must be heavily hitting the list -
* it's a rather theoretical concern.
*/
/* don't use these structs directly */
struct atomlist_item {
atomic_uintptr_t next;
};
#define atomlist_itemp(val) ((struct atomlist_item *)atomptr_p(val))
struct atomlist_head {
atomic_uintptr_t first, last;
atomic_size_t count;
};
/* use as:
*
* PREDECL_ATOMLIST(namelist);
* struct name {
* struct namelist_item nlitem;
* }
* DECLARE_ATOMLIST(namelist, struct name, nlitem);
*/
#define PREDECL_ATOMLIST(prefix) \
struct prefix ## _head { struct atomlist_head ah; }; \
struct prefix ## _item { struct atomlist_item ai; }; \
MACRO_REQUIRE_SEMICOLON() /* end */
#define INIT_ATOMLIST(var) { }
#define DECLARE_ATOMLIST(prefix, type, field) \
macro_inline void prefix ## _add_head(struct prefix##_head *h, type *item) \
{ atomlist_add_head(&h->ah, &item->field.ai); } \
macro_inline void prefix ## _add_tail(struct prefix##_head *h, type *item) \
{ atomlist_add_tail(&h->ah, &item->field.ai); } \
macro_inline void prefix ## _del_hint(struct prefix##_head *h, type *item, \
atomic_atomptr_t *hint) \
{ atomlist_del_hint(&h->ah, &item->field.ai, hint); } \
macro_inline type *prefix ## _del(struct prefix##_head *h, type *item) \
{ atomlist_del_hint(&h->ah, &item->field.ai, NULL); \
/* TODO: Return NULL if not found */ \
return item; } \
macro_inline type *prefix ## _pop(struct prefix##_head *h) \
{ char *p = (char *)atomlist_pop(&h->ah); \
return p ? (type *)(p - offsetof(type, field)) : NULL; } \
macro_inline type *prefix ## _first(struct prefix##_head *h) \
{ char *p = atomptr_p(atomic_load_explicit(&h->ah.first, \
memory_order_acquire)); \
return p ? (type *)(p - offsetof(type, field)) : NULL; } \
macro_inline type *prefix ## _next(struct prefix##_head *h, type *item) \
{ char *p = atomptr_p(atomic_load_explicit(&item->field.ai.next, \
memory_order_acquire)); \
return p ? (type *)(p - offsetof(type, field)) : NULL; } \
macro_inline type *prefix ## _next_safe(struct prefix##_head *h, type *item) \
{ return item ? prefix##_next(h, item) : NULL; } \
macro_inline size_t prefix ## _count(struct prefix##_head *h) \
{ return atomic_load_explicit(&h->ah.count, memory_order_relaxed); } \
macro_inline void prefix ## _init(struct prefix##_head *h) \
{ \
memset(h, 0, sizeof(*h)); \
} \
macro_inline void prefix ## _fini(struct prefix##_head *h) \
{ \
assert(prefix ## _count(h) == 0); \
memset(h, 0, sizeof(*h)); \
} \
MACRO_REQUIRE_SEMICOLON() /* end */
/* add_head:
* - contention on ->first pointer
* - return implies completion
*/
void atomlist_add_head(struct atomlist_head *h, struct atomlist_item *item);
/* add_tail:
* - concurrent add_tail can cause wait but has progress guarantee
* - return does NOT imply completion. completion is only guaranteed after
* all other add_tail operations that started before this add_tail have
* completed as well.
*/
void atomlist_add_tail(struct atomlist_head *h, struct atomlist_item *item);
/* del/del_hint:
*
* OWNER MUST HOLD REFERENCE ON ITEM TO BE DELETED, ENSURING NO OTHER THREAD
* WILL TRY TO DELETE THE SAME ITEM. DELETING INCLUDES pop().
*
* as with all deletions, threads that started reading earlier may still hold
* pointers to the deleted item. completion is however guaranteed for all
* reads starting later.
*/
void atomlist_del_hint(struct atomlist_head *h, struct atomlist_item *item,
atomic_atomptr_t *hint);
/* pop:
*
* as with all deletions, threads that started reading earlier may still hold
* pointers to the deleted item. completion is however guaranteed for all
* reads starting later.
*/
struct atomlist_item *atomlist_pop(struct atomlist_head *h);
struct atomsort_item {
atomic_atomptr_t next;
};
#define atomsort_itemp(val) ((struct atomsort_item *)atomptr_p(val))
struct atomsort_head {
atomic_atomptr_t first;
atomic_size_t count;
};
#define _PREDECL_ATOMSORT(prefix) \
struct prefix ## _head { struct atomsort_head ah; }; \
struct prefix ## _item { struct atomsort_item ai; }; \
MACRO_REQUIRE_SEMICOLON() /* end */
#define INIT_ATOMSORT_UNIQ(var) { }
#define INIT_ATOMSORT_NONUNIQ(var) { }
#define _DECLARE_ATOMSORT(prefix, type, field, cmpfn_nuq, cmpfn_uq) \
macro_inline void prefix ## _init(struct prefix##_head *h) \
{ \
memset(h, 0, sizeof(*h)); \
} \
macro_inline void prefix ## _fini(struct prefix##_head *h) \
{ \
assert(h->ah.count == 0); \
memset(h, 0, sizeof(*h)); \
} \
macro_inline type *prefix ## _add(struct prefix##_head *h, type *item) \
{ \
struct atomsort_item *p; \
p = atomsort_add(&h->ah, &item->field.ai, cmpfn_uq); \
return container_of_null(p, type, field.ai); \
} \
macro_inline type *prefix ## _first(struct prefix##_head *h) \
{ \
struct atomsort_item *p; \
p = atomptr_p(atomic_load_explicit(&h->ah.first, \
memory_order_acquire)); \
return container_of_null(p, type, field.ai); \
} \
macro_inline type *prefix ## _next(struct prefix##_head *h, type *item) \
{ \
struct atomsort_item *p; \
p = atomptr_p(atomic_load_explicit(&item->field.ai.next, \
memory_order_acquire)); \
return container_of_null(p, type, field.ai); \
} \
macro_inline type *prefix ## _next_safe(struct prefix##_head *h, type *item) \
{ \
return item ? prefix##_next(h, item) : NULL; \
} \
atomic_find_warn \
macro_inline type *prefix ## _find_gteq(struct prefix##_head *h, \
const type *item) \
{ \
type *p = prefix ## _first(h); \
while (p && cmpfn_nuq(&p->field.ai, &item->field.ai) < 0) \
p = prefix ## _next(h, p); \
return p; \
} \
atomic_find_warn \
macro_inline type *prefix ## _find_lt(struct prefix##_head *h, \
const type *item) \
{ \
type *p = prefix ## _first(h), *prev = NULL; \
while (p && cmpfn_nuq(&p->field.ai, &item->field.ai) < 0) \
p = prefix ## _next(h, (prev = p)); \
return prev; \
} \
macro_inline void prefix ## _del_hint(struct prefix##_head *h, type *item, \
atomic_atomptr_t *hint) \
{ \
atomsort_del_hint(&h->ah, &item->field.ai, hint); \
} \
macro_inline type *prefix ## _del(struct prefix##_head *h, type *item) \
{ \
atomsort_del_hint(&h->ah, &item->field.ai, NULL); \
/* TODO: Return NULL if not found */ \
return item; \
} \
macro_inline size_t prefix ## _count(struct prefix##_head *h) \
{ \
return atomic_load_explicit(&h->ah.count, memory_order_relaxed); \
} \
macro_inline type *prefix ## _pop(struct prefix##_head *h) \
{ \
struct atomsort_item *p = atomsort_pop(&h->ah); \
return p ? container_of(p, type, field.ai) : NULL; \
} \
MACRO_REQUIRE_SEMICOLON() /* end */
#define PREDECL_ATOMSORT_UNIQ(prefix) \
_PREDECL_ATOMSORT(prefix)
#define DECLARE_ATOMSORT_UNIQ(prefix, type, field, cmpfn) \
\
macro_inline int prefix ## __cmp(const struct atomsort_item *a, \
const struct atomsort_item *b) \
{ \
return cmpfn(container_of(a, type, field.ai), \
container_of(b, type, field.ai)); \
} \
\
_DECLARE_ATOMSORT(prefix, type, field, \
prefix ## __cmp, prefix ## __cmp); \
\
atomic_find_warn \
macro_inline type *prefix ## _find(struct prefix##_head *h, const type *item) \
{ \
type *p = prefix ## _first(h); \
int cmpval = 0; \
while (p && (cmpval = cmpfn(p, item)) < 0) \
p = prefix ## _next(h, p); \
if (!p || cmpval > 0) \
return NULL; \
return p; \
} \
MACRO_REQUIRE_SEMICOLON() /* end */
#define PREDECL_ATOMSORT_NONUNIQ(prefix) \
_PREDECL_ATOMSORT(prefix)
#define DECLARE_ATOMSORT_NONUNIQ(prefix, type, field, cmpfn) \
\
macro_inline int prefix ## __cmp(const struct atomsort_item *a, \
const struct atomsort_item *b) \
{ \
return cmpfn(container_of(a, type, field.ai), \
container_of(b, type, field.ai)); \
} \
macro_inline int prefix ## __cmp_uq(const struct atomsort_item *a, \
const struct atomsort_item *b) \
{ \
int cmpval = cmpfn(container_of(a, type, field.ai), \
container_of(b, type, field.ai)); \
if (cmpval) \
return cmpval; \
if (a < b) \
return -1; \
if (a > b) \
return 1; \
return 0; \
} \
\
_DECLARE_ATOMSORT(prefix, type, field, \
prefix ## __cmp, prefix ## __cmp_uq); \
MACRO_REQUIRE_SEMICOLON() /* end */
struct atomsort_item *atomsort_add(struct atomsort_head *h,
struct atomsort_item *item, int (*cmpfn)(
const struct atomsort_item *,
const struct atomsort_item *));
void atomsort_del_hint(struct atomsort_head *h,
struct atomsort_item *item, atomic_atomptr_t *hint);
struct atomsort_item *atomsort_pop(struct atomsort_head *h);
#ifdef __cplusplus
}
#endif
#endif /* _FRR_ATOMLIST_H */