+// SPDX-FileCopyrightText: 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+//
+// SPDX-License-Identifier: LGPL-2.1-or-later
+
#ifndef _URCU_WAIT_H
#define _URCU_WAIT_H
/*
- * urcu-wait.h
- *
* Userspace RCU library wait/wakeup management
- *
- * Copyright (c) 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
- *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation; either
- * version 2.1 of the License, or (at your option) any later version.
- *
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- * Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <urcu/assert.h>
#include <urcu/uatomic.h>
#include <urcu/wfstack.h>
+#include <urcu/futex.h>
#include "urcu-die.h"
/*
goto skip_futex_wait;
caa_cpu_relax();
}
- while (futex_noasync(&wait->state, FUTEX_WAIT, URCU_WAIT_WAITING,
- NULL, NULL, 0)) {
+ while (uatomic_read(&wait->state) == URCU_WAIT_WAITING) {
+ if (!futex_noasync(&wait->state, FUTEX_WAIT, URCU_WAIT_WAITING, NULL, NULL, 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
+ * URCU_WAIT_WAITING (spurious wakeups). Check
+ * the value again in user-space to validate
+ * whether it really differs from
+ * URCU_WAIT_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. */
urcu_die(errno);