7 * Userspace RCU library wait/wakeup management
9 * Copyright (c) 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
11 * This library is free software; you can redistribute it and/or
12 * modify it under the terms of the GNU Lesser General Public
13 * License as published by the Free Software Foundation; either
14 * version 2.1 of the License, or (at your option) any later version.
16 * This library is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
19 * Lesser General Public License for more details.
21 * You should have received a copy of the GNU Lesser General Public
22 * License along with this library; if not, write to the Free Software
23 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
26 #include <urcu/uatomic.h>
27 #include <urcu/wfstack.h>
31 * Number of busy-loop attempts before waiting on futex for grace period
34 #define URCU_WAIT_ATTEMPTS 1000
36 enum urcu_wait_state
{
37 /* URCU_WAIT_WAITING is compared directly (futex compares it). */
38 URCU_WAIT_WAITING
= 0,
39 /* non-zero are used as masks. */
40 URCU_WAIT_WAKEUP
= (1 << 0),
41 URCU_WAIT_RUNNING
= (1 << 1),
42 URCU_WAIT_TEARDOWN
= (1 << 2),
45 struct urcu_wait_node
{
46 struct cds_wfs_node node
;
47 int32_t state
; /* enum urcu_wait_state */
50 #define URCU_WAIT_NODE_INIT(name, _state) \
53 #define DEFINE_URCU_WAIT_NODE(name, state) \
54 struct urcu_wait_node name = URCU_WAIT_NODE_INIT(name, state)
56 #define DECLARE_URCU_WAIT_NODE(name) \
57 struct urcu_wait_node name
59 struct urcu_wait_queue
{
60 struct cds_wfs_stack stack
;
63 #define URCU_WAIT_QUEUE_HEAD_INIT(name) \
64 { .stack.head = CDS_WFS_END, .stack.lock = PTHREAD_MUTEX_INITIALIZER }
66 #define DECLARE_URCU_WAIT_QUEUE(name) \
67 struct urcu_wait_queue name
69 #define DEFINE_URCU_WAIT_QUEUE(name) \
70 struct urcu_wait_queue name = URCU_WAIT_QUEUE_HEAD_INIT(name)
73 struct cds_wfs_head
*head
;
77 * Add ourself atomically to a wait queue. Return 0 if queue was
78 * previously empty, else return 1.
79 * A full memory barrier is issued before being added to the wait queue.
82 bool urcu_wait_add(struct urcu_wait_queue
*queue
,
83 struct urcu_wait_node
*node
)
85 return cds_wfs_push(&queue
->stack
, &node
->node
);
89 * Atomically move all waiters from wait queue into our local struct
93 void urcu_move_waiters(struct urcu_waiters
*waiters
,
94 struct urcu_wait_queue
*queue
)
96 waiters
->head
= __cds_wfs_pop_all(&queue
->stack
);
100 void urcu_wait_set_state(struct urcu_wait_node
*node
,
101 enum urcu_wait_state state
)
107 void urcu_wait_node_init(struct urcu_wait_node
*node
,
108 enum urcu_wait_state state
)
110 urcu_wait_set_state(node
, state
);
111 cds_wfs_node_init(&node
->node
);
115 * Note: urcu_adaptative_wake_up needs "value" to stay allocated
116 * throughout its execution. In this scheme, the waiter owns the node
117 * memory, and we only allow it to free this memory when it receives the
118 * URCU_WAIT_TEARDOWN flag.
121 void urcu_adaptative_wake_up(struct urcu_wait_node
*wait
)
124 assert(uatomic_read(&wait
->state
) == URCU_WAIT_WAITING
);
125 uatomic_set(&wait
->state
, URCU_WAIT_WAKEUP
);
126 if (!(uatomic_read(&wait
->state
) & URCU_WAIT_RUNNING
)) {
127 if (futex_noasync(&wait
->state
, FUTEX_WAKE
, 1,
131 /* Allow teardown of struct urcu_wait memory. */
132 uatomic_or(&wait
->state
, URCU_WAIT_TEARDOWN
);
136 * Caller must initialize "value" to URCU_WAIT_WAITING before passing its
137 * memory to waker thread.
140 void urcu_adaptative_busy_wait(struct urcu_wait_node
*wait
)
144 /* Load and test condition before read state */
146 for (i
= 0; i
< URCU_WAIT_ATTEMPTS
; i
++) {
147 if (uatomic_read(&wait
->state
) != URCU_WAIT_WAITING
)
148 goto skip_futex_wait
;
151 while (futex_noasync(&wait
->state
, FUTEX_WAIT
, URCU_WAIT_WAITING
,
155 /* Value already changed. */
156 goto skip_futex_wait
;
158 /* Retry if interrupted by signal. */
159 break; /* Get out of switch. */
161 /* Unexpected error. */
167 /* Tell waker thread than we are running. */
168 uatomic_or(&wait
->state
, URCU_WAIT_RUNNING
);
171 * Wait until waker thread lets us know it's ok to tear down
172 * memory allocated for struct urcu_wait.
174 for (i
= 0; i
< URCU_WAIT_ATTEMPTS
; i
++) {
175 if (uatomic_read(&wait
->state
) & URCU_WAIT_TEARDOWN
)
179 while (!(uatomic_read(&wait
->state
) & URCU_WAIT_TEARDOWN
))
181 assert(uatomic_read(&wait
->state
) & URCU_WAIT_TEARDOWN
);
185 void urcu_wake_all_waiters(struct urcu_waiters
*waiters
)
187 struct cds_wfs_node
*iter
, *iter_n
;
189 /* Wake all waiters in our stack head */
190 cds_wfs_for_each_blocking_safe(waiters
->head
, iter
, iter_n
) {
191 struct urcu_wait_node
*wait_node
=
192 caa_container_of(iter
, struct urcu_wait_node
, node
);
194 /* Don't wake already running threads */
195 if (wait_node
->state
& URCU_WAIT_RUNNING
)
197 urcu_adaptative_wake_up(wait_node
);
201 #endif /* _URCU_WAIT_H */
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