2 * Copyright (C) 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
3 * Copyright (C) 2017 Jérémie Galarneau <jeremie.galarneau@efficios.com>
5 * SPDX-License-Identifier: LGPL-2.1-only
10 #include <urcu/uatomic.h>
11 #include <urcu/futex.h>
16 * Number of busy-loop attempts before waiting on futex.
18 #define WAIT_ATTEMPTS 1000
21 /* WAITER_WAITING is compared directly (futex compares it). */
23 /* non-zero are used as masks. */
24 WAITER_WOKEN_UP
= (1 << 0),
25 WAITER_RUNNING
= (1 << 1),
26 WAITER_TEARDOWN
= (1 << 2),
30 void lttng_waiter_init(struct lttng_waiter
*waiter
)
32 cds_wfs_node_init(&waiter
->wait_queue_node
);
33 uatomic_set(&waiter
->state
, WAITER_WAITING
);
38 * User must init "waiter" before passing its memory to waker thread.
41 void lttng_waiter_wait(struct lttng_waiter
*waiter
)
45 DBG("Beginning of waiter wait period");
46 /* Load and test condition before read state */
48 for (i
= 0; i
< WAIT_ATTEMPTS
; i
++) {
49 if (uatomic_read(&waiter
->state
) != WAITER_WAITING
) {
54 while (futex_noasync(&waiter
->state
, FUTEX_WAIT
, WAITER_WAITING
,
58 /* Value already changed. */
61 /* Retry if interrupted by signal. */
62 break; /* Get out of switch. */
64 /* Unexpected error. */
65 PERROR("futex_noasync");
71 /* Tell waker thread than we are running. */
72 uatomic_or(&waiter
->state
, WAITER_RUNNING
);
75 * Wait until waker thread lets us know it's ok to tear down
76 * memory allocated for struct lttng_waiter.
78 for (i
= 0; i
< WAIT_ATTEMPTS
; i
++) {
79 if (uatomic_read(&waiter
->state
) & WAITER_TEARDOWN
) {
84 while (!(uatomic_read(&waiter
->state
) & WAITER_TEARDOWN
)) {
87 LTTNG_ASSERT(uatomic_read(&waiter
->state
) & WAITER_TEARDOWN
);
88 DBG("End of waiter wait period");
92 * Note: lttng_waiter_wake needs waiter to stay allocated throughout its
93 * execution. In this scheme, the waiter owns the node memory, and we only allow
94 * it to free this memory when it sees the WAITER_TEARDOWN flag.
97 void lttng_waiter_wake_up(struct lttng_waiter
*waiter
)
100 LTTNG_ASSERT(uatomic_read(&waiter
->state
) == WAITER_WAITING
);
101 uatomic_set(&waiter
->state
, WAITER_WOKEN_UP
);
102 if (!(uatomic_read(&waiter
->state
) & WAITER_RUNNING
)) {
103 if (futex_noasync(&waiter
->state
, FUTEX_WAKE
, 1,
104 NULL
, NULL
, 0) < 0) {
105 PERROR("futex_noasync");
109 /* Allow teardown of struct urcu_wait memory. */
110 uatomic_or(&waiter
->state
, WAITER_TEARDOWN
);
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