| 1 | #ifndef _URCU_WFSTACK_STATIC_H |
| 2 | #define _URCU_WFSTACK_STATIC_H |
| 3 | |
| 4 | /* |
| 5 | * wfstack-static.h |
| 6 | * |
| 7 | * Userspace RCU library - Stack with Wait-Free push, Blocking pop. |
| 8 | * |
| 9 | * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See wfstack.h for linking |
| 10 | * dynamically with the userspace rcu library. |
| 11 | * |
| 12 | * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| 13 | * |
| 14 | * This library is free software; you can redistribute it and/or |
| 15 | * modify it under the terms of the GNU Lesser General Public |
| 16 | * License as published by the Free Software Foundation; either |
| 17 | * version 2.1 of the License, or (at your option) any later version. |
| 18 | * |
| 19 | * This library is distributed in the hope that it will be useful, |
| 20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 22 | * Lesser General Public License for more details. |
| 23 | * |
| 24 | * You should have received a copy of the GNU Lesser General Public |
| 25 | * License along with this library; if not, write to the Free Software |
| 26 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
| 27 | */ |
| 28 | |
| 29 | #include <pthread.h> |
| 30 | #include <assert.h> |
| 31 | #include <poll.h> |
| 32 | #include <urcu/compiler.h> |
| 33 | #include <urcu/uatomic_arch.h> |
| 34 | |
| 35 | #ifdef __cplusplus |
| 36 | extern "C" { |
| 37 | #endif |
| 38 | |
| 39 | #define CDS_WF_STACK_END ((void *)0x1UL) |
| 40 | #define CDS_WFS_ADAPT_ATTEMPTS 10 /* Retry if being set */ |
| 41 | #define CDS_WFS_WAIT 10 /* Wait 10 ms if being set */ |
| 42 | |
| 43 | void _cds_wfs_node_init(struct cds_wfs_node *node) |
| 44 | { |
| 45 | node->next = NULL; |
| 46 | } |
| 47 | |
| 48 | void _cds_wfs_init(struct cds_wfs_stack *s) |
| 49 | { |
| 50 | int ret; |
| 51 | |
| 52 | s->head = CDS_WF_STACK_END; |
| 53 | ret = pthread_mutex_init(&s->lock, NULL); |
| 54 | assert(!ret); |
| 55 | } |
| 56 | |
| 57 | void _cds_wfs_push(struct cds_wfs_stack *s, struct cds_wfs_node *node) |
| 58 | { |
| 59 | struct cds_wfs_node *old_head; |
| 60 | |
| 61 | assert(node->next == NULL); |
| 62 | /* |
| 63 | * uatomic_xchg() implicit memory barrier orders earlier stores to node |
| 64 | * (setting it to NULL) before publication. |
| 65 | */ |
| 66 | old_head = uatomic_xchg(&s->head, node); |
| 67 | /* |
| 68 | * At this point, dequeuers see a NULL node->next, they should busy-wait |
| 69 | * until node->next is set to old_head. |
| 70 | */ |
| 71 | CMM_STORE_SHARED(node->next, old_head); |
| 72 | } |
| 73 | |
| 74 | /* |
| 75 | * Returns NULL if stack is empty. |
| 76 | */ |
| 77 | struct cds_wfs_node * |
| 78 | ___cds_wfs_pop_blocking(struct cds_wfs_stack *s) |
| 79 | { |
| 80 | struct cds_wfs_node *head, *next; |
| 81 | int attempt = 0; |
| 82 | |
| 83 | retry: |
| 84 | head = CMM_LOAD_SHARED(s->head); |
| 85 | if (head == CDS_WF_STACK_END) |
| 86 | return NULL; |
| 87 | /* |
| 88 | * Adaptative busy-looping waiting for push to complete. |
| 89 | */ |
| 90 | while ((next = CMM_LOAD_SHARED(head->next)) == NULL) { |
| 91 | if (++attempt >= CDS_WFS_ADAPT_ATTEMPTS) { |
| 92 | poll(NULL, 0, CDS_WFS_WAIT); /* Wait for 10ms */ |
| 93 | attempt = 0; |
| 94 | } else |
| 95 | caa_cpu_relax(); |
| 96 | } |
| 97 | if (uatomic_cmpxchg(&s->head, head, next) == head) |
| 98 | return head; |
| 99 | else |
| 100 | goto retry; /* Concurrent modification. Retry. */ |
| 101 | } |
| 102 | |
| 103 | struct cds_wfs_node * |
| 104 | _cds_wfs_pop_blocking(struct cds_wfs_stack *s) |
| 105 | { |
| 106 | struct cds_wfs_node *retnode; |
| 107 | int ret; |
| 108 | |
| 109 | ret = pthread_mutex_lock(&s->lock); |
| 110 | assert(!ret); |
| 111 | retnode = ___cds_wfs_pop_blocking(s); |
| 112 | ret = pthread_mutex_unlock(&s->lock); |
| 113 | assert(!ret); |
| 114 | return retnode; |
| 115 | } |
| 116 | |
| 117 | #ifdef __cplusplus |
| 118 | } |
| 119 | #endif |
| 120 | |
| 121 | #endif /* _URCU_WFSTACK_STATIC_H */ |