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MINOR: fd: slightly optimize the fd_takeover double-CAS loop

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The loop in fd_takeover() around the double-CAS is conditionned on
a previous value of old_masks[0] that always matches tid_bit on the
first iteration because it does not result from the atomic op but
from a pre-loaded value. Let's set the result of the atomic op there
instead so that the conflict between threads can be detected earlier
and before performing the double-word CAS.
This commit is contained in:
Willy Tarreau 2020-06-18 08:05:15 +02:00
parent c460c91633
commit 4297363de3
1 changed files with 4 additions and 3 deletions
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7
src/fd.c
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@ -367,14 +367,15 @@ int fd_takeover(int fd, void *expected_owner)
unsigned long old_masks[2];
unsigned long new_masks[2];
old_masks[0] = tid_bit;
old_masks[1] = fdtab[fd].thread_mask;
new_masks[0] = new_masks[1] = tid_bit;
old_masks[0] = _HA_ATOMIC_OR(&fdtab[fd].running_mask, tid_bit);
old_masks[1] = fdtab[fd].thread_mask;
/* protect ourself against a delete then an insert for the same fd,
* if it happens, then the owner will no longer be the expected
* connection.
*/
_HA_ATOMIC_OR(&fdtab[fd].running_mask, tid_bit);
if (fdtab[fd].owner != expected_owner) {
_HA_ATOMIC_AND(&fdtab[fd].running_mask, ~tid_bit);
return -1;