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