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DOC/MINOR: list: fixing MT_LIST_LOCK_ELT macro documentation

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MT_LIST_LOCK_ELT macro was documented with an ambiguous
usage restriction, implying that concurrent list deletion
was not supported.

But it seems that either the code has evolved, or the comment is
wrong because the locking behavior implemented here is exactly
the same one used in MT_LIST_DELETE, and no such restriction is
described for MT_LIST_DELETE.

I made some tests to make sure concurrent MT_LIST_DELETE (or deletion
from mt_list_for_each_entry_safe) don't cause unexepected results.

At the present time, this macro is not used, this fix only
targets upcoming developments that might rely on this.

No backport needed.
This commit is contained in:
Aurelien DARRAGON 2022-10-20 09:42:23 +02:00 committed by Christopher Faulet
parent bcaa401646
commit 18c284c126
1 changed files with 5 additions and 3 deletions
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8
include/haproxy/list.h
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@ -604,10 +604,12 @@
*/ */
#define MT_LIST_INLIST(el) ((el)->next != (el)) #define MT_LIST_INLIST(el) ((el)->next != (el))
/* Lock an element in the list, to be sure it won't be removed. /* Lock an element in the list, to be sure it won't be removed nor
* It needs to be synchronized somehow to be sure it's not removed * accessed by another thread while the lock is held.
* from the list in the meanwhile. * Locking behavior is inspired from MT_LIST_DELETE macro,
* thus this macro can safely be used concurrently with MT_LIST_DELETE.
* This returns a struct mt_list, that will be needed at unlock time. * This returns a struct mt_list, that will be needed at unlock time.
* (using MT_LIST_UNLOCK_ELT)
*/ */
#define MT_LIST_LOCK_ELT(_el) \ #define MT_LIST_LOCK_ELT(_el) \
({ \ ({ \