file_fadvise.go

package file

import (
	"bufio"
	"bytes"
	"io"
	"os"
	"path/filepath"

	"linkfog.com/public/lib/fadvise"
	"linkfog.com/public/lib/l"
	"linkfog.com/public/option"
)

func FadviseSwitch(f *os.File) {
	if err := fadvise.Switch(f); err != nil {
		l.Error(err)
	}
}

func PurgeSwitch(path string) {
	if !option.Fadvise {
		return
	}
	if err := purge(path); err != nil {
		l.Error(err)
	}
}

func purge(path string) error {
	f, err := os.Open(path)
	if err != nil {
		return err
	}
	defer f.Close()
	err = fadvise.Switch(f)
	if err != nil {
		return err
	}
	return nil
}

func ReadFileFadvise(name string) ([]byte, error) {
	f, err := os.Open(name)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	defer FadviseSwitch(f)
	var size int
	if info, err := f.Stat(); err == nil {
		size64 := info.Size()
		if int64(int(size64)) == size64 {
			size = int(size64)
		}
	}
	size++ // one byte for final read at EOF

	// If a file claims a small size, read at least 512 bytes.
	// In particular, files in Linux's /proc claim size 0 but
	// then do not work right if read in small pieces,
	// so an initial read of 1 byte would not work correctly.
	if size < 512 {
		size = 512
	}

	data := make([]byte, 0, size)
	for {
		if len(data) >= cap(data) {
			d := append(data[:cap(data)], 0)
			data = d[:len(data)]
		}
		n, err := f.Read(data[len(data):cap(data)])
		data = data[:len(data)+n]
		if err != nil {
			if err == io.EOF {
				err = nil
			}
			return data, err
		}
	}
}

// ReadFileIntoBuffer reads an arbitrary file into a buffer.
func ReadFileIntoBufferFadvise(filename string, buf *bytes.Buffer) (int64, error) {
	f, err := os.Open(filename)
	if err != nil {
		return -1, err
	}
	defer f.Close()
	defer FadviseSwitch(f)
	return buf.ReadFrom(f)
}

func ReadFileLineFadvise(filePath string) (line string, err error) {
	if !exist(filePath) {
		return line, l.WrapError("file not exist.")
	}

	fi, err := os.Open(filePath)
	if err != nil {
		return line, l.WrapError("open file err:", err, "filePath:", filePath)
	}
	defer fi.Close()
	defer FadviseSwitch(fi)
	br := bufio.NewReader(fi)
	for {
		a, _, c := br.ReadLine()
		if c == io.EOF {
			break
		}
		return string(a), err
	}
	return line, err
}

func exist(filename string) bool {
	_, err := os.Stat(filename)
	return err == nil || !os.IsNotExist(err)
}

// walk folder to purge file page cache
func WalkPurgeSwitch(path string) {
	if !option.Fadvise {
		return
	}
	if err := walkPurge(path); err != nil {
		l.Error(err)
	}
}

func walkPurge(path string) error {
	return filepath.Walk(path,
		func(path string, info os.FileInfo, err error) error {
			if err != nil {
				l.Error(err)
				return nil
			}
			if !info.Mode().IsRegular() {
				return nil
			}
			err = purge(path)
			if err != nil {
				l.Error(err)
			}
			return nil
		})
}