Willy Tarreau | 374b442 | 2020-06-02 17:46:16 +0200 | [diff] [blame] | 1 | /* |
| 2 | * include/haproxy/xref.h |
| 3 | * Atomic cross-references between two elements - functions |
| 4 | * |
| 5 | * Copyright (C) 2017 Thierry Fournier <thierry.fournier@ozon.io> |
| 6 | * Copyright (C) 2020 Willy Tarreau - w@1wt.eu |
| 7 | * |
| 8 | * Permission is hereby granted, free of charge, to any person obtaining |
| 9 | * a copy of this software and associated documentation files (the |
| 10 | * "Software"), to deal in the Software without restriction, including |
| 11 | * without limitation the rights to use, copy, modify, merge, publish, |
| 12 | * distribute, sublicense, and/or sell copies of the Software, and to |
| 13 | * permit persons to whom the Software is furnished to do so, subject to |
| 14 | * the following conditions: |
| 15 | * |
| 16 | * The above copyright notice and this permission notice shall be |
| 17 | * included in all copies or substantial portions of the Software. |
| 18 | * |
| 19 | * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, |
| 20 | * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES |
| 21 | * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND |
| 22 | * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT |
| 23 | * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, |
| 24 | * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING |
| 25 | * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR |
| 26 | * OTHER DEALINGS IN THE SOFTWARE. |
| 27 | */ |
| 28 | #ifndef __HAPROXY_XREF_H__ |
| 29 | #define __HAPROXY_XREF_H__ |
| 30 | |
Willy Tarreau | 374b442 | 2020-06-02 17:46:16 +0200 | [diff] [blame] | 31 | #include <haproxy/xref-t.h> |
| 32 | |
| 33 | /* xref is used to create relation between two elements. |
| 34 | * Once an element is released, it breaks the relation. If the |
| 35 | * relation is already broken, it frees the xref struct. |
| 36 | * The pointer between two elements is sort of a refcount with |
| 37 | * max value 1. The relation is only between two elements. |
| 38 | * The pointer and the type of elements a and b are conventional. |
| 39 | */ |
| 40 | |
| 41 | static inline void xref_create(struct xref *xref_a, struct xref *xref_b) |
| 42 | { |
| 43 | xref_a->peer = xref_b; |
| 44 | xref_b->peer = xref_a; |
| 45 | } |
| 46 | |
| 47 | static inline struct xref *xref_get_peer_and_lock(struct xref *xref) |
| 48 | { |
| 49 | struct xref *local; |
| 50 | struct xref *remote; |
| 51 | |
| 52 | while (1) { |
| 53 | |
| 54 | /* Get the local pointer to the peer. */ |
| 55 | local = _HA_ATOMIC_XCHG(&xref->peer, XREF_BUSY); |
| 56 | __ha_barrier_atomic_store(); |
| 57 | |
| 58 | /* If the local pointer is NULL, the peer no longer exists. */ |
| 59 | if (local == NULL) { |
| 60 | xref->peer = NULL; |
| 61 | return NULL; |
| 62 | } |
| 63 | |
| 64 | /* If the local pointeru is BUSY, the peer try to acquire the |
| 65 | * lock. We retry the process. |
| 66 | */ |
| 67 | if (local == XREF_BUSY) |
| 68 | continue; |
| 69 | |
| 70 | /* We are locked, the peer can't disappear, try to acquire |
| 71 | * the pper's lock. Note that remote can't be NULL. |
| 72 | */ |
| 73 | remote = _HA_ATOMIC_XCHG(&local->peer, XREF_BUSY); |
| 74 | |
| 75 | /* The remote lock is BUSY, We retry the process. */ |
| 76 | if (remote == XREF_BUSY) { |
| 77 | xref->peer = local; |
| 78 | __ha_barrier_store(); |
| 79 | continue; |
| 80 | } |
| 81 | |
| 82 | /* We have the lock, we return the value of the xref. */ |
| 83 | return local; |
| 84 | } |
| 85 | } |
| 86 | |
| 87 | static inline void xref_unlock(struct xref *xref, struct xref *peer) |
| 88 | { |
| 89 | /* Release the peer. */ |
| 90 | peer->peer = xref; |
| 91 | |
| 92 | __ha_barrier_store(); |
| 93 | |
| 94 | /* Release myself. */ |
| 95 | xref->peer = peer; |
| 96 | } |
| 97 | |
| 98 | static inline void xref_disconnect(struct xref *xref, struct xref *peer) |
| 99 | { |
| 100 | peer->peer = NULL; |
| 101 | __ha_barrier_store(); |
| 102 | xref->peer = NULL; |
| 103 | } |
| 104 | |
| 105 | #endif /* __HAPROXY_XREF_H__ */ |