85 lines
1.9 KiB
C
85 lines
1.9 KiB
C
#ifndef __XREF_H__
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#define __XREF_H__
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#include <common/hathreads.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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struct xref {
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struct xref *peer;
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};
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#define XREF_BUSY ((struct xref *)1)
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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 cant disapear, 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 /* __XREF_H__ */
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