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MINOR: list: adding MT_LIST_APPEND_LOCKED macro

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adding a new mt macro: MT_LIST_APPEND_LOCKED.

This macro may be used to append an item to an existing
list, like MT_LIST_APPEND.

But here the item will be forced into locked/busy state
prior to appending, so that it is already referenced
in the list while still preventing concurrent accesses
until we decide to unlock it.

The macro returns a struct mt_list "np", that is needed
at unlock time using regular MT_LIST_UNLOCK_ELT macro.
This commit is contained in:
Aurelien DARRAGON 2022-10-20 17:37:51 +02:00 committed by Christopher Faulet
parent 18c284c126
commit e951c3435c
1 changed files with 34 additions and 0 deletions
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34
include/haproxy/list.h
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@ -416,6 +416,40 @@
(_ret); \
})
/*
* Add an item at the end of a list.
* It is assumed the element can't already be in a list, so it isn't checked
* Item will be added in busy/locked state, so that it is already
* referenced in the list but no other thread can use it until we're ready.
*
* This returns a struct mt_list, that will be needed at unlock time.
* (using MT_LIST_UNLOCK_ELT)
*/
#define MT_LIST_APPEND_LOCKED(_lh, _el) \
({ \
struct mt_list np; \
struct mt_list *lh = (_lh), *el = (_el); \
(el)->next = MT_LIST_BUSY; \
(el)->prev = MT_LIST_BUSY; \
for (;;__ha_cpu_relax()) { \
struct mt_list *n; \
struct mt_list *p; \
p = _HA_ATOMIC_XCHG(&(lh)->prev, MT_LIST_BUSY); \
if (p == MT_LIST_BUSY) \
continue; \
n = _HA_ATOMIC_XCHG(&p->next, MT_LIST_BUSY); \
if (n == MT_LIST_BUSY) { \
(lh)->prev = p; \
__ha_barrier_store(); \
continue; \
} \
np.prev = p; \
np.next = n; \
break; \
} \
(np); \
})
/*
* Detach a list from its head. A pointer to the first element is returned
* and the list is closed. If the list was empty, NULL is returned. This may