EventFDWrapper.h

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/*
 * Copyright 2014-present Facebook, Inc.
 *
 * 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.
 */

#pragma once

#ifndef FOLLY_NO_CONFIG
#include <folly/folly-config.h>
#endif

#if __has_include(<features.h>)
#include <features.h>
#endif

#if defined(__GLIBC__) && !defined(__APPLE__)
#if __GLIBC_PREREQ(2, 9)
#define FOLLY_GLIBC_2_9
#endif
#endif

// <sys/eventfd.h> doesn't exist on older glibc versions
#ifdef FOLLY_GLIBC_2_9
#include <sys/eventfd.h>
#else /* !def FOLLY_GLIBC_2_9 */

#include <fcntl.h>
#include <sys/syscall.h>
#include <unistd.h>

// Use existing __NR_eventfd2 if already defined
// Values from the Linux kernel source:
// arch/x86/include/asm/unistd_{32,64}.h
#ifndef __NR_eventfd2
#if FOLLY_X64
/* nolint */
#define __NR_eventfd2 290
#elif defined(__i386__)
/* nolint */
#define __NR_eventfd2 328
#else
#error "Can't define __NR_eventfd2 for your architecture."
#endif
#endif

enum {
  EFD_SEMAPHORE = 1,
#define EFD_SEMAPHORE EFD_SEMAPHORE
  EFD_CLOEXEC = 02000000,
#define EFD_CLOEXEC EFD_CLOEXEC
  EFD_NONBLOCK = 04000
#define EFD_NONBLOCK EFD_NONBLOCK
};

// http://www.kernel.org/doc/man-pages/online/pages/man2/eventfd.2.html
// Use the eventfd2 system call, as in glibc 2.9+
// (requires kernel 2.6.30+)
#define eventfd(initval, flags) syscall(__NR_eventfd2, (initval), (flags))

#endif /* !(defined(__GLIBC__) && __GLIBC_PREREQ(2, 9)) */