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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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