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116 lines
3.6 KiB
Go
116 lines
3.6 KiB
Go
// Copyright 2011 Evan Shaw. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// This file defines the common package interface and contains a little bit of
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// factored out logic.
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// Package mmap allows mapping files into memory. It tries to provide a simple, reasonably portable interface,
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// but doesn't go out of its way to abstract away every little platform detail.
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// This specifically means:
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// * forked processes may or may not inherit mappings
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// * a file's timestamp may or may not be updated by writes through mappings
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// * specifying a size larger than the file's actual size can increase the file's size
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// * If the mapped file is being modified by another process while your program's running, don't expect consistent results between platforms
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package mmap
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import (
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"errors"
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"os"
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"reflect"
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"unsafe"
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)
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const (
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// RDONLY maps the memory read-only.
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// Attempts to write to the MMap object will result in undefined behavior.
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RDONLY = 0
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// RDWR maps the memory as read-write. Writes to the MMap object will update the
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// underlying file.
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RDWR = 1 << iota
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// COPY maps the memory as copy-on-write. Writes to the MMap object will affect
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// memory, but the underlying file will remain unchanged.
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COPY
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// If EXEC is set, the mapped memory is marked as executable.
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EXEC
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)
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const (
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// If the ANON flag is set, the mapped memory will not be backed by a file.
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ANON = 1 << iota
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)
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// MMap represents a file mapped into memory.
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type MMap []byte
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// Map maps an entire file into memory.
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// If ANON is set in flags, f is ignored.
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func Map(f *os.File, prot, flags int) (MMap, error) {
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return MapRegion(f, -1, prot, flags, 0)
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}
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// MapRegion maps part of a file into memory.
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// The offset parameter must be a multiple of the system's page size.
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// If length < 0, the entire file will be mapped.
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// If ANON is set in flags, f is ignored.
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func MapRegion(f *os.File, length int, prot, flags int, offset int64) (MMap, error) {
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if offset%int64(os.Getpagesize()) != 0 {
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return nil, errors.New("offset parameter must be a multiple of the system's page size")
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}
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var fd uintptr
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if flags&ANON == 0 {
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fd = uintptr(f.Fd())
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if length < 0 {
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fi, err := f.Stat()
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if err != nil {
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return nil, err
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}
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length = int(fi.Size())
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}
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} else {
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if length <= 0 {
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return nil, errors.New("anonymous mapping requires non-zero length")
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}
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fd = ^uintptr(0)
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}
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return mmap(length, uintptr(prot), uintptr(flags), fd, offset)
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}
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func (m *MMap) header() *reflect.SliceHeader {
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return (*reflect.SliceHeader)(unsafe.Pointer(m))
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}
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// Lock keeps the mapped region in physical memory, ensuring that it will not be
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// swapped out.
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func (m MMap) Lock() error {
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dh := m.header()
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return lock(dh.Data, uintptr(dh.Len))
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}
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// Unlock reverses the effect of Lock, allowing the mapped region to potentially
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// be swapped out.
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// If m is already unlocked, aan error will result.
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func (m MMap) Unlock() error {
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dh := m.header()
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return unlock(dh.Data, uintptr(dh.Len))
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}
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// Flush synchronizes the mapping's contents to the file's contents on disk.
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func (m MMap) Flush() error {
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dh := m.header()
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return flush(dh.Data, uintptr(dh.Len))
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}
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// Unmap deletes the memory mapped region, flushes any remaining changes, and sets
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// m to nil.
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// Trying to read or write any remaining references to m after Unmap is called will
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// result in undefined behavior.
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// Unmap should only be called on the slice value that was originally returned from
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// a call to Map. Calling Unmap on a derived slice may cause errors.
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func (m *MMap) Unmap() error {
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dh := m.header()
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err := unmap(dh.Data, uintptr(dh.Len))
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*m = nil
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return err
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}
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