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Diffstat (limited to 'include/haproxy/xref.h')
| -rw-r--r-- | include/haproxy/xref.h | 105 |
1 files changed, 105 insertions, 0 deletions
diff --git a/include/haproxy/xref.h b/include/haproxy/xref.h new file mode 100644 index 0000000..42eed58 --- /dev/null +++ b/include/haproxy/xref.h @@ -0,0 +1,105 @@ +/* + * include/haproxy/xref.h + * Atomic cross-references between two elements - functions + * + * Copyright (C) 2017 Thierry Fournier <thierry.fournier@ozon.io> + * Copyright (C) 2020 Willy Tarreau - w@1wt.eu + * + * Permission is hereby granted, free of charge, to any person obtaining + * a copy of this software and associated documentation files (the + * "Software"), to deal in the Software without restriction, including + * without limitation the rights to use, copy, modify, merge, publish, + * distribute, sublicense, and/or sell copies of the Software, and to + * permit persons to whom the Software is furnished to do so, subject to + * the following conditions: + * + * The above copyright notice and this permission notice shall be + * included in all copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, + * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES + * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND + * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT + * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, + * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR + * OTHER DEALINGS IN THE SOFTWARE. + */ +#ifndef __HAPROXY_XREF_H__ +#define __HAPROXY_XREF_H__ + +#include <haproxy/xref-t.h> + +/* xref is used to create relation between two elements. + * Once an element is released, it breaks the relation. If the + * relation is already broken, it frees the xref struct. + * The pointer between two elements is sort of a refcount with + * max value 1. The relation is only between two elements. + * The pointer and the type of elements a and b are conventional. + */ + +static inline void xref_create(struct xref *xref_a, struct xref *xref_b) +{ + xref_a->peer = xref_b; + xref_b->peer = xref_a; +} + +static inline struct xref *xref_get_peer_and_lock(struct xref *xref) +{ + struct xref *local; + struct xref *remote; + + while (1) { + + /* Get the local pointer to the peer. */ + local = _HA_ATOMIC_XCHG(&xref->peer, XREF_BUSY); + __ha_barrier_atomic_store(); + + /* If the local pointer is NULL, the peer no longer exists. */ + if (local == NULL) { + xref->peer = NULL; + return NULL; + } + + /* If the local pointeru is BUSY, the peer try to acquire the + * lock. We retry the process. + */ + if (local == XREF_BUSY) + continue; + + /* We are locked, the peer can't disappear, try to acquire + * the pper's lock. Note that remote can't be NULL. + */ + remote = _HA_ATOMIC_XCHG(&local->peer, XREF_BUSY); + + /* The remote lock is BUSY, We retry the process. */ + if (remote == XREF_BUSY) { + xref->peer = local; + __ha_barrier_store(); + continue; + } + + /* We have the lock, we return the value of the xref. */ + return local; + } +} + +static inline void xref_unlock(struct xref *xref, struct xref *peer) +{ + /* Release the peer. */ + peer->peer = xref; + + __ha_barrier_store(); + + /* Release myself. */ + xref->peer = peer; +} + +static inline void xref_disconnect(struct xref *xref, struct xref *peer) +{ + peer->peer = NULL; + __ha_barrier_store(); + xref->peer = NULL; +} + +#endif /* __HAPROXY_XREF_H__ */ |