+++ /dev/null
-/*
- * Copyright (C) 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
- * Copyright (C) 2017 Jérémie Galarneau <jeremie.galarneau@efficios.com>
- *
- * SPDX-License-Identifier: LGPL-2.1-only
- *
- */
-
-#include "waiter.h"
-#include <urcu/uatomic.h>
-#include <urcu/futex.h>
-#include "error.h"
-#include <poll.h>
-
-/*
- * Number of busy-loop attempts before waiting on futex.
- */
-#define WAIT_ATTEMPTS 1000
-
-enum waiter_state {
- /* WAITER_WAITING is compared directly (futex compares it). */
- WAITER_WAITING = 0,
- /* non-zero are used as masks. */
- WAITER_WOKEN_UP = (1 << 0),
- WAITER_RUNNING = (1 << 1),
- WAITER_TEARDOWN = (1 << 2),
-};
-
-LTTNG_HIDDEN
-void lttng_waiter_init(struct lttng_waiter *waiter)
-{
- cds_wfs_node_init(&waiter->wait_queue_node);
- uatomic_set(&waiter->state, WAITER_WAITING);
- cmm_smp_mb();
-}
-
-/*
- * User must init "waiter" before passing its memory to waker thread.
- */
-LTTNG_HIDDEN
-void lttng_waiter_wait(struct lttng_waiter *waiter)
-{
- unsigned int i;
-
- DBG("Beginning of waiter wait period");
- /* Load and test condition before read state */
- cmm_smp_rmb();
- for (i = 0; i < WAIT_ATTEMPTS; i++) {
- if (uatomic_read(&waiter->state) != WAITER_WAITING) {
- goto skip_futex_wait;
- }
- caa_cpu_relax();
- }
- while (futex_noasync(&waiter->state, FUTEX_WAIT, WAITER_WAITING,
- NULL, NULL, 0)) {
- switch (errno) {
- case EWOULDBLOCK:
- /* Value already changed. */
- goto skip_futex_wait;
- case EINTR:
- /* Retry if interrupted by signal. */
- break; /* Get out of switch. */
- default:
- /* Unexpected error. */
- PERROR("futex_noasync");
- abort();
- }
- }
-skip_futex_wait:
-
- /* Tell waker thread than we are running. */
- uatomic_or(&waiter->state, WAITER_RUNNING);
-
- /*
- * Wait until waker thread lets us know it's ok to tear down
- * memory allocated for struct lttng_waiter.
- */
- for (i = 0; i < WAIT_ATTEMPTS; i++) {
- if (uatomic_read(&waiter->state) & WAITER_TEARDOWN) {
- break;
- }
- caa_cpu_relax();
- }
- while (!(uatomic_read(&waiter->state) & WAITER_TEARDOWN)) {
- poll(NULL, 0, 10);
- }
- LTTNG_ASSERT(uatomic_read(&waiter->state) & WAITER_TEARDOWN);
- DBG("End of waiter wait period");
-}
-
-/*
- * Note: lttng_waiter_wake needs waiter to stay allocated throughout its
- * execution. In this scheme, the waiter owns the node memory, and we only allow
- * it to free this memory when it sees the WAITER_TEARDOWN flag.
- */
-LTTNG_HIDDEN
-void lttng_waiter_wake_up(struct lttng_waiter *waiter)
-{
- cmm_smp_mb();
- LTTNG_ASSERT(uatomic_read(&waiter->state) == WAITER_WAITING);
- uatomic_set(&waiter->state, WAITER_WOKEN_UP);
- if (!(uatomic_read(&waiter->state) & WAITER_RUNNING)) {
- if (futex_noasync(&waiter->state, FUTEX_WAKE, 1,
- NULL, NULL, 0) < 0) {
- PERROR("futex_noasync");
- abort();
- }
- }
- /* Allow teardown of struct urcu_wait memory. */
- uatomic_or(&waiter->state, WAITER_TEARDOWN);
-}