readahead

README

readahead

Asynchronous read-ahead for Go readers

This package will allow you to add readhead to any reader. This means a separate goroutine will perform reads from your upstream reader, so you can request from this reader without delay.

This is helpful for splitting an input stream into concurrent processing, and also helps smooth out bursts of input or output.

This should be fully transparent, except that once an error has been returned from the Reader, it will not recover. A panic will be caught and returned as an error.

The readahead object also fulfills the io.WriterTo interface, which is likely to speed up io.Copy and other code that use the interface.

See an introduction: An Async Read-ahead Package for Go

usage

To get the package use go get -u github.com/klauspost/readahead.

Here is a simple example that does file copy. Error handling has been omitted for brevity.

input, _ := os.Open("input.txt")
output, _ := os.Create("output.txt")
defer input.Close()
defer output.Close()

// Create a read-ahead Reader with default settings
ra := readahead.NewReader(input)
defer ra.Close()

// Copy the content to our output
_, _ = io.Copy(output, ra)

settings

You can finetune the read-ahead for your specific use case, and adjust the number of buffers and the size of each buffer.

The default the size of each buffer is 1MB, and there are 4 buffers. Do not make your buffers too small since there is a small overhead for passing buffers between goroutines. Other than that you are free to experiment with buffer sizes.

contributions

On this project contributions in terms of new features is limited to:

• Features that are widely usable and
• Features that have extensive tests

This package is meant to be simple and stable, so therefore these strict requirements.

The only feature I have considered is supporting the io.Seeker interface. I currently do not plan to add it myself, but if you can show a clean and well-tested way to implementing it, I will consider to merge it. If not, I will be happy to link to it.

license

This package is released under the MIT license. See the supplied LICENSE file for more info.

Documentation

Overview

The readahead package will do asynchronous read-ahead from an input io.Reader and make the data available as an io.Reader.

This should be fully transparent, except that once an error has been returned from the Reader, it will not recover.

The readahead object also fulfills the io.WriterTo interface, which is likely to speed up copies.

Package home: https://github.com/klauspost/readahead

Example

package main

import (
	"bytes"
	"fmt"
	"io"

	"github.com/klauspost/readahead"
)

func main() {
	// Buf is our input.
	buf := bytes.NewBufferString("Example data")

	// Create a Reader with default settings
	reader := readahead.NewReader(buf)
	defer reader.Close()

	// Copy the content to dst
	var dst = &bytes.Buffer{}
	_, err := io.Copy(dst, reader)
	if err != nil {
		panic("error when reading: " + err.Error())
	}

	fmt.Println(dst.String())
}

Output:
Example data

Index

• func NewReadCloser(rd io.ReadCloser) io.ReadCloser
• func NewReadCloserSize(rc io.ReadCloser, buffers, size int) (io.ReadCloser, error)
• func NewReader(rd io.Reader) io.ReadCloser
• func NewReaderSize(rd io.Reader, buffers, size int) (io.ReadCloser, error)

Examples

• Package

Functions

func NewReadCloser

func NewReadCloser(rd io.ReadCloser) io.ReadCloser

New returns a reader that will asynchronously read from the supplied reader into 4 buffers of 1MB each.

It will start reading from the input at once, maybe even before this function has returned.

The input can be read from the returned reader. When done use Close() to release the buffers, which will also close the supplied closer.

func NewReadCloserSize

func NewReadCloserSize(rc io.ReadCloser, buffers, size int) (io.ReadCloser, error)

NewReadCloserSize returns a reader with a custom number of buffers and size. buffers is the number of queued buffers and size is the size of each buffer in bytes.

func NewReader

func NewReader(rd io.Reader) io.ReadCloser

New returns a reader that will asynchronously read from the supplied reader into 4 buffers of 1MB each.

It will start reading from the input at once, maybe even before this function has returned.

The input can be read from the returned reader. When done use Close() to release the buffers.

func NewReaderSize

func NewReaderSize(rd io.Reader, buffers, size int) (io.ReadCloser, error)

NewReaderSize returns a reader with a custom number of buffers and size. buffers is the number of queued buffers and size is the size of each buffer in bytes.