-- c508ee8bcc38dad1019c0ad744c47ac70efd36b7 by Derek Mauro <dmauro@google.com>: Opensource the Linux specific SpinLock Wait/Wake implementation. PiperOrigin-RevId: 209420888 -- c13113e19973d496f3e798c0e6d5569c78e41466 by Derek Mauro <dmauro@google.com>: Fix build error from https://github.com/abseil/abseil-cpp/issues/159 PiperOrigin-RevId: 209152118 GitOrigin-RevId: c508ee8bcc38dad1019c0ad744c47ac70efd36b7 Change-Id: I1a287df973198f9e26936d8f91031bb354db0c71pull/163/head
parent
ad5c960b2e
commit
d8cfe9f2a7
5 changed files with 80 additions and 3 deletions
@ -0,0 +1,72 @@ |
||||
// Copyright 2018 The Abseil Authors. |
||||
// |
||||
// Licensed under the Apache License, Version 2.0 (the "License"); |
||||
// you may not use this file except in compliance with the License. |
||||
// You may obtain a copy of the License at |
||||
// |
||||
// http://www.apache.org/licenses/LICENSE-2.0 |
||||
// |
||||
// Unless required by applicable law or agreed to in writing, software |
||||
// distributed under the License is distributed on an "AS IS" BASIS, |
||||
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
||||
// See the License for the specific language governing permissions and |
||||
// limitations under the License. |
||||
// |
||||
// This file is a Linux-specific part of spinlock_wait.cc |
||||
|
||||
#include <linux/futex.h> |
||||
#include <sys/syscall.h> |
||||
#include <unistd.h> |
||||
|
||||
#include <atomic> |
||||
#include <cerrno> |
||||
#include <climits> |
||||
#include <cstdint> |
||||
#include <ctime> |
||||
|
||||
#include "absl/base/attributes.h" |
||||
|
||||
// The SpinLock lockword is `std::atomic<uint32_t>`. Here we assert that |
||||
// `std::atomic<uint32_t>` is bitwise equivalent of the `int` expected |
||||
// by SYS_futex. We also assume that reads/writes done to the lockword |
||||
// by SYS_futex have rational semantics with regard to the |
||||
// std::atomic<> API. C++ provides no guarantees of these assumptions, |
||||
// but they are believed to hold in practice. |
||||
static_assert(sizeof(std::atomic<uint32_t>) == sizeof(int), |
||||
"SpinLock lockword has the wrong size for a futex"); |
||||
|
||||
// Some Android headers are missing these definitions even though they |
||||
// support these futex operations. |
||||
#ifdef __BIONIC__ |
||||
#ifndef SYS_futex |
||||
#define SYS_futex __NR_futex |
||||
#endif |
||||
#ifndef FUTEX_PRIVATE_FLAG |
||||
#define FUTEX_PRIVATE_FLAG 128 |
||||
#endif |
||||
#endif |
||||
|
||||
extern "C" { |
||||
|
||||
ABSL_ATTRIBUTE_WEAK void AbslInternalSpinLockDelay( |
||||
std::atomic<uint32_t> *w, uint32_t value, int loop, |
||||
absl::base_internal::SchedulingMode) { |
||||
if (loop != 0) { |
||||
int save_errno = errno; |
||||
struct timespec tm; |
||||
tm.tv_sec = 0; |
||||
// Increase the delay; we expect (but do not rely on) explicit wakeups. |
||||
// We don't rely on explicit wakeups because we intentionally allow for |
||||
// a race on the kSpinLockSleeper bit. |
||||
tm.tv_nsec = 16 * absl::base_internal::SpinLockSuggestedDelayNS(loop); |
||||
syscall(SYS_futex, w, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, value, &tm); |
||||
errno = save_errno; |
||||
} |
||||
} |
||||
|
||||
ABSL_ATTRIBUTE_WEAK void AbslInternalSpinLockWake(std::atomic<uint32_t> *w, |
||||
bool all) { |
||||
syscall(SYS_futex, w, FUTEX_WAKE | FUTEX_PRIVATE_FLAG, all ? INT_MAX : 1, 0); |
||||
} |
||||
|
||||
} // extern "C" |
Loading…
Reference in new issue