blob: bdf292d883081f875b785b12ff4c7a75516d066c [file] [log] [blame]
#ifndef __XREF_H__
#define __XREF_H__
#include <haproxy/atomic.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.
*/
struct xref {
struct xref *peer;
};
#define XREF_BUSY ((struct xref *)1)
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 /* __XREF_H__ */