License: common: error_query: fix typo in SPDX specifier

[lttng-tools.git] / src / common / waiter.cpp

diff --git a/src/common/waiter.cpp b/src/common/waiter.cpp
index 3ddb68feb7c76dd91f09bec9d7664c02224627a2..d185e299720617e64e7514d114e33cea4a0eb386 100644 (file)
--- a/src/common/waiter.cpp
+++ b/src/common/waiter.cpp
@@ -6,11 +6,13 @@
  *
  */
 
-#include "waiter.hpp"
-#include <urcu/uatomic.h>
-#include <urcu/futex.h>
 #include "error.hpp"
+#include "macros.hpp"
+#include "waiter.hpp"
+
 #include <poll.h>
+#include <urcu/futex.h>
+#include <urcu/uatomic.h>
 
 /*
  * Number of busy-loop attempts before waiting on futex.
@@ -19,11 +21,11 @@
 
 enum waiter_state {
        /* WAITER_WAITING is compared directly (futex compares it). */
-       WAITER_WAITING =        0,
+       WAITER_WAITING = 0,
        /* non-zero are used as masks. */
-       WAITER_WOKEN_UP =       (1 << 0),
-       WAITER_RUNNING =        (1 << 1),
-       WAITER_TEARDOWN =       (1 << 2),
+       WAITER_WOKEN_UP = (1 << 0),
+       WAITER_RUNNING = (1 << 1),
+       WAITER_TEARDOWN = (1 << 2),
 };
 
 void lttng_waiter_init(struct lttng_waiter *waiter)
@@ -40,24 +42,39 @@ void lttng_waiter_wait(struct lttng_waiter *waiter)
 {
        unsigned int i;
 
-       DBG("Beginning of waiter wait period");
-       /* Load and test condition before read state */
+       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)) {
+
+       while (uatomic_read(&waiter->state) == WAITER_WAITING) {
+               if (!futex_noasync(
+                           &waiter->state, FUTEX_WAIT, WAITER_WAITING, nullptr, nullptr, 0)) {
+                       /*
+                        * Prior queued wakeups queued by unrelated code
+                        * using the same address can cause futex wait to
+                        * return 0 even through the futex value is still
+                        * WAITER_WAITING (spurious wakeups). Check
+                        * the value again in user-space to validate
+                        * whether it really differs from WAITER_WAITING.
+                        */
+                       continue;
+               }
+
                switch (errno) {
-               case EWOULDBLOCK:
+               case EAGAIN:
                        /* Value already changed. */
                        goto skip_futex_wait;
                case EINTR:
                        /* Retry if interrupted by signal. */
-                       break;  /* Get out of switch. */
+                       break; /* Get out of switch. Check again. */
                default:
                        /* Unexpected error. */
                        PERROR("futex_noasync");
@@ -77,13 +94,16 @@ skip_futex_wait:
                if (uatomic_read(&waiter->state) & WAITER_TEARDOWN) {
                        break;
                }
+
                caa_cpu_relax();
        }
+
        while (!(uatomic_read(&waiter->state) & WAITER_TEARDOWN)) {
-               poll(NULL, 0, 10);
+               poll(nullptr, 0, 10);
        }
+
        LTTNG_ASSERT(uatomic_read(&waiter->state) & WAITER_TEARDOWN);
-       DBG("End of waiter wait period");
+       DBG("End of waiter \"wait\" period");
 }
 
 /*
@@ -91,18 +111,49 @@ skip_futex_wait:
  * 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.
  */
-void lttng_waiter_wake_up(struct lttng_waiter *waiter)
+void lttng_waiter_wake(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) {
+               if (futex_noasync(&waiter->state, FUTEX_WAKE, 1, nullptr, nullptr, 0) < 0) {
                        PERROR("futex_noasync");
                        abort();
                }
        }
+
        /* Allow teardown of struct urcu_wait memory. */
        uatomic_or(&waiter->state, WAITER_TEARDOWN);
 }
+
+void lttng_wait_queue_init(struct lttng_wait_queue *queue)
+{
+       cds_wfs_init(&queue->stack);
+}
+
+void lttng_wait_queue_add(struct lttng_wait_queue *queue, struct lttng_waiter *waiter)
+{
+       (void) cds_wfs_push(&queue->stack, &waiter->wait_queue_node);
+}
+
+void lttng_wait_queue_wake_all(struct lttng_wait_queue *queue)
+{
+       cds_wfs_head *waiters;
+       cds_wfs_node *iter, *iter_n;
+
+       /* Move all waiters from the queue to our local stack. */
+       waiters = __cds_wfs_pop_all(&queue->stack);
+
+       /* Wake all waiters in our stack head. */
+       cds_wfs_for_each_blocking_safe (waiters, iter, iter_n) {
+               auto *waiter = lttng::utils::container_of(iter, &lttng_waiter::wait_queue_node);
+
+               /* Don't wake already running threads. */
+               if (waiter->state & WAITER_RUNNING) {
+                       continue;
+               }
+
+               lttng_waiter_wake(waiter);
+       }
+}