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tevent: introduce DLIST_DEMOTE_SHORT()

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It turns out that the overhead of DLIST_DEMOTE() implemented
as DLIST_REMOVE();DLIST_ADD_END(), is very high if the list
contains only 1 or 2 elements.

The next commits will make use of DLIST_DEMOTE_SHORT() for
multiplexing multiple tevent_fd structures for a single fd
and the most important and common case is a list with just
one element.

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
This commit is contained in:
Stefan Metzmacher 2023-01-30 16:10:07 +01:00 committed by Ralph Boehme
parent d895c98c50
commit 30d22631a6
1 changed files with 21 additions and 0 deletions
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21
lib/tevent/tevent_dlinklist.h
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@ -156,6 +156,27 @@ do { \
DLIST_ADD_END(list, p); \
} while (0)
/*
* like DLIST_DEMOTE(), but optimized
* for short lists with 0, 1 or 2 elements
*/
#define DLIST_DEMOTE_SHORT(list, p) \
do { \
if ((list) == NULL) { \
/* no reason to demote, just add */ \
DLIST_ADD(list, p); \
} else if ((list)->prev == (p)) { \
/* optimize if p is last */ \
} else if ((list) == (p)) { \
/* optimize if p is first */ \
(list)->prev->next = (p); \
(list) = (p)->next; \
(p)->next = NULL; \
} else { \
DLIST_DEMOTE(list, p); \
} \
} while (0)
/*
concatenate two lists - putting all elements of the 2nd list at the
end of the first list.