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106 lines
3.1 KiB
106 lines
3.1 KiB
5 months ago
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/*
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* include/haproxy/xref.h
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* Atomic cross-references between two elements - functions
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*
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* Copyright (C) 2017 Thierry Fournier <thierry.fournier@ozon.io>
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* Copyright (C) 2020 Willy Tarreau - w@1wt.eu
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
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* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
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* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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* OTHER DEALINGS IN THE SOFTWARE.
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*/
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#ifndef __HAPROXY_XREF_H__
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#define __HAPROXY_XREF_H__
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#include <haproxy/xref-t.h>
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/* xref is used to create relation between two elements.
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* Once an element is released, it breaks the relation. If the
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* relation is already broken, it frees the xref struct.
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* The pointer between two elements is sort of a refcount with
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* max value 1. The relation is only between two elements.
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* The pointer and the type of elements a and b are conventional.
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*/
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static inline void xref_create(struct xref *xref_a, struct xref *xref_b)
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{
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xref_a->peer = xref_b;
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xref_b->peer = xref_a;
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}
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static inline struct xref *xref_get_peer_and_lock(struct xref *xref)
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{
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struct xref *local;
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struct xref *remote;
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while (1) {
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/* Get the local pointer to the peer. */
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local = _HA_ATOMIC_XCHG(&xref->peer, XREF_BUSY);
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__ha_barrier_atomic_store();
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/* If the local pointer is NULL, the peer no longer exists. */
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if (local == NULL) {
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xref->peer = NULL;
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return NULL;
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}
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/* If the local pointeru is BUSY, the peer try to acquire the
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* lock. We retry the process.
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*/
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if (local == XREF_BUSY)
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continue;
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/* We are locked, the peer can't disappear, try to acquire
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* the pper's lock. Note that remote can't be NULL.
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*/
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remote = _HA_ATOMIC_XCHG(&local->peer, XREF_BUSY);
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/* The remote lock is BUSY, We retry the process. */
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if (remote == XREF_BUSY) {
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xref->peer = local;
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__ha_barrier_store();
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continue;
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}
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/* We have the lock, we return the value of the xref. */
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return local;
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}
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}
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static inline void xref_unlock(struct xref *xref, struct xref *peer)
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{
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/* Release the peer. */
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peer->peer = xref;
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__ha_barrier_store();
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/* Release myself. */
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xref->peer = peer;
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}
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static inline void xref_disconnect(struct xref *xref, struct xref *peer)
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{
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peer->peer = NULL;
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__ha_barrier_store();
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xref->peer = NULL;
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}
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#endif /* __HAPROXY_XREF_H__ */
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