64 lines
1.8 KiB
Go
64 lines
1.8 KiB
Go
// +build !windows
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/*
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* Copyright 2017 Dgraph Labs, Inc. and Contributors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package y
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import (
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"os"
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"syscall"
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"unsafe"
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"golang.org/x/sys/unix"
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)
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// Mmap uses the mmap system call to memory-map a file. If writable is true,
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// memory protection of the pages is set so that they may be written to as well.
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func Mmap(fd *os.File, writable bool, size int64) ([]byte, error) {
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mtype := unix.PROT_READ
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if writable {
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mtype |= unix.PROT_WRITE
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}
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return unix.Mmap(int(fd.Fd()), 0, int(size), mtype, unix.MAP_SHARED)
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}
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// Munmap unmaps a previously mapped slice.
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func Munmap(b []byte) error {
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return unix.Munmap(b)
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}
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// Madvise uses the madvise system call to give advise about the use of memory
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// when using a slice that is memory-mapped to a file. Set the readahead flag to
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// false if page references are expected in random order.
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func Madvise(b []byte, readahead bool) error {
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flags := unix.MADV_NORMAL
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if !readahead {
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flags = unix.MADV_RANDOM
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}
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return madvise(b, flags)
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}
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// This is required because the unix package does not support the madvise system call on OS X.
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func madvise(b []byte, advice int) (err error) {
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_, _, e1 := syscall.Syscall(syscall.SYS_MADVISE, uintptr(unsafe.Pointer(&b[0])),
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uintptr(len(b)), uintptr(advice))
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if e1 != 0 {
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err = e1
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}
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return
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}
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