92 lines
2.3 KiB
Go
92 lines
2.3 KiB
Go
// +build linux darwin dragonfly freebsd netbsd openbsd
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// +build !appengine
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package msgp
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import (
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"os"
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"syscall"
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)
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// ReadFile reads a file into 'dst' using
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// a read-only memory mapping. Consequently,
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// the file must be mmap-able, and the
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// Unmarshaler should never write to
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// the source memory. (Methods generated
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// by the msgp tool obey that constraint, but
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// user-defined implementations may not.)
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//
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// Reading and writing through file mappings
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// is only efficient for large files; small
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// files are best read and written using
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// the ordinary streaming interfaces.
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//
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func ReadFile(dst Unmarshaler, file *os.File) error {
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stat, err := file.Stat()
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if err != nil {
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return err
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}
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data, err := syscall.Mmap(int(file.Fd()), 0, int(stat.Size()), syscall.PROT_READ, syscall.MAP_SHARED)
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if err != nil {
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return err
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}
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adviseRead(data)
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_, err = dst.UnmarshalMsg(data)
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uerr := syscall.Munmap(data)
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if err == nil {
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err = uerr
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}
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return err
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}
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// MarshalSizer is the combination
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// of the Marshaler and Sizer
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// interfaces.
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type MarshalSizer interface {
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Marshaler
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Sizer
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}
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// WriteFile writes a file from 'src' using
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// memory mapping. It overwrites the entire
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// contents of the previous file.
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// The mapping size is calculated
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// using the `Msgsize()` method
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// of 'src', so it must produce a result
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// equal to or greater than the actual encoded
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// size of the object. Otherwise,
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// a fault (SIGBUS) will occur.
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//
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// Reading and writing through file mappings
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// is only efficient for large files; small
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// files are best read and written using
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// the ordinary streaming interfaces.
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//
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// NOTE: The performance of this call
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// is highly OS- and filesystem-dependent.
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// Users should take care to test that this
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// performs as expected in a production environment.
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// (Linux users should run a kernel and filesystem
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// that support fallocate(2) for the best results.)
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func WriteFile(src MarshalSizer, file *os.File) error {
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sz := src.Msgsize()
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err := fallocate(file, int64(sz))
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if err != nil {
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return err
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}
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data, err := syscall.Mmap(int(file.Fd()), 0, sz, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED)
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if err != nil {
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return err
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}
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adviseWrite(data)
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chunk := data[:0]
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chunk, err = src.MarshalMsg(chunk)
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if err != nil {
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return err
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}
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uerr := syscall.Munmap(data)
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if uerr != nil {
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return uerr
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}
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return file.Truncate(int64(len(chunk)))
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}
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