X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=src%2Fcommon%2Fwaiter.cpp;h=d185e299720617e64e7514d114e33cea4a0eb386;hb=75f62e5383c6ea1f62fb488a94f4a8f98400db71;hp=3ddb68feb7c76dd91f09bec9d7664c02224627a2;hpb=c9e313bc594f40a86eed237dce222c0fc99c957f;p=lttng-tools.git

diff --git a/src/common/waiter.cpp b/src/common/waiter.cpp
index 3ddb68feb..d185e2997 100644
--- 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);
+	}
+}