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- // -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
- /* Copyright (c) 2009, Google Inc.
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions are
- * met:
- *
- * * Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- * * Redistributions in binary form must reproduce the above
- * copyright notice, this list of conditions and the following disclaimer
- * in the documentation and/or other materials provided with the
- * distribution.
- * * Neither the name of Google Inc. nor the names of its
- * contributors may be used to endorse or promote products derived from
- * this software without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- *
- * ---
- * This file is a Linux-specific part of spinlock_internal.cc
- */
- #include <errno.h>
- #include <sched.h>
- #include <time.h>
- #include <limits.h>
- #include "base/linux_syscall_support.h"
- #define FUTEX_WAIT 0
- #define FUTEX_WAKE 1
- #define FUTEX_PRIVATE_FLAG 128
- static bool have_futex;
- static int futex_private_flag = FUTEX_PRIVATE_FLAG;
- namespace {
- static struct InitModule {
- InitModule() {
- int x = 0;
- // futexes are ints, so we can use them only when
- // that's the same size as the lockword_ in SpinLock.
- have_futex = (sizeof (Atomic32) == sizeof (int) &&
- sys_futex(&x, FUTEX_WAKE, 1, NULL, NULL, 0) >= 0);
- if (have_futex &&
- sys_futex(&x, FUTEX_WAKE | futex_private_flag, 1, NULL, NULL, 0) < 0) {
- futex_private_flag = 0;
- }
- }
- } init_module;
- } // anonymous namespace
- namespace base {
- namespace internal {
- void SpinLockDelay(volatile Atomic32 *w, int32 value, int loop) {
- if (loop != 0) {
- int save_errno = errno;
- struct timespec tm;
- tm.tv_sec = 0;
- if (have_futex) {
- tm.tv_nsec = base::internal::SuggestedDelayNS(loop);
- } else {
- tm.tv_nsec = 2000001; // above 2ms so linux 2.4 doesn't spin
- }
- if (have_futex) {
- tm.tv_nsec *= 16; // increase the delay; we expect explicit wakeups
- sys_futex(reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
- FUTEX_WAIT | futex_private_flag,
- value, reinterpret_cast<struct kernel_timespec *>(&tm),
- NULL, 0);
- } else {
- nanosleep(&tm, NULL);
- }
- errno = save_errno;
- }
- }
- void SpinLockWake(volatile Atomic32 *w, bool all) {
- if (have_futex) {
- sys_futex(reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
- FUTEX_WAKE | futex_private_flag, all? INT_MAX : 1,
- NULL, NULL, 0);
- }
- }
- } // namespace internal
- } // namespace base
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