Ecosyste.ms: Awesome

An open API service indexing awesome lists of open source software.

Awesome Lists | Featured Topics | Projects

https://github.com/michaelnisi/speculum

Transform concurrently
https://github.com/michaelnisi/speculum

concurrent-streams nodejs transform-streams

Last synced: about 2 months ago
JSON representation

Transform concurrently

Awesome Lists containing this project

README 

        
[![Build Status](https://secure.travis-ci.org/michaelnisi/speculum.svg)](http://travis-ci.org/michaelnisi/speculum)

[![Coverage Status](https://coveralls.io/repos/github/michaelnisi/speculum/badge.svg?branch=master)](https://coveralls.io/github/michaelnisi/speculum?branch=master)



# speculum - transform concurrently



**speculum** is a stream multiplier. This [Node.js](https://nodesjs.org) package implements an interface that wraps multiple transform streams into a single, concurrently processing, [stream.Transform](https://nodejs.org/api/stream.html#stream_class_stream_transform). In use cases where result order is not paramount, **speculum** can reduce run time.



An IO-heavy transform stream’s run time *T* grows linearly with the number *N* of chunks (units of IO work) *C*:



*T = N * C*



**speculum** divides the run time by the number of concurrent streams *X*:



*T = N * C / X*



So far for theory.



## Example



Here is a, somewhat contrived but runnable, example comparing the run times from single to ten concurrent streams:



```js

'use strict'



// example - measure one to ten concurrent streams



const assert = require('assert')

const speculum = require('speculum')

const stream = require('stream')

const util = require('util')



// A transform that does asynchronous work.

util.inherits(Echo, stream.Transform)

function Echo (opts) {

  if (!(this instanceof Echo)) {

    return new Echo(opts)

  }

  stream.Transform.call(this, opts)

}

Echo.prototype._transform = function (chunk, enc, cb) {

  setTimeout(() => {

    this.push(chunk)

    cb()

  }, 100)

}



// An input stream to read from.

util.inherits(Count, stream.Readable)

function Count (opts, max) {

  stream.Readable.call(this, opts)

  this.count = 0

  this.max = max

}

Count.prototype._read = function () {

  let ok = false

  do {

    ok = this.push(String(this.count++))

  } while (this.count < this.max && ok)

  if (this.count >= this.max) {

    this.push(null)

  }

}



// Leverage x streams to transform, delayed echoing in this example, data from

// our readable stream.

function run (x, cb) {

  const s = speculum(null, Echo, x)

  s.on('end', cb)

  s.on('error', cb)



  const reader = new Count({ highWaterMark: 0 }, 10)



  reader.pipe(s).resume()

}



function measure (x, cb) {

  function time (t) {

    return t[0] * 1e9 + t[1]

  }

  const t = process.hrtime()

  run(x, (er) => {

    const lat = time(process.hrtime(t))

    console.log(x + ' X took ' + (lat / 1e6).toFixed(2) + ' ms')

    cb(er)

  })

}



(function go (max, x = 1) {

  if (x > max) return

  measure(x, (er) => {

    assert(!er, er)

    go(max, x + 1)

  })

})(10)

```



You can run this with:



```

$ node example.js

```



On this MacBook Air (11-inch, Mid 2011), with Node v6.7.0, I get:



```

1 X took 1088.49 ms

2 X took 525.67 ms

3 X took 411.52 ms

4 X took 317.99 ms

5 X took 210.97 ms

6 X took 210.99 ms

7 X took 210.68 ms

8 X took 210.24 ms

9 X took 211.61 ms

10 X took 104.25 ms

```



## Considerations



Clearly, we have to balance workload and overhead to use this efficiently. Specifically, we need an idea of how many chunks our stream may need to process, before we can choose an effective number of concurrent streams. But efficiency, of course, varies depending on duration and consistence of the work to be done inside our multiplied stream.



**speculum** is a good fit if you want to reduce run time by leveraging existing transform streams concurrently, not minding unordered output. In other use cases, where you might be writing a concurrent transform stream from scratch, try [throughv](https://github.com/mcollina/throughv).



## Exports



### speculum(opts, create, x = 1)



- `opts` `Object() | null | undefined` Options passed to the stream constructor.

- `create` `function` A constructor function applied to create transform streams.

- `x` `Number() | null | undefined` The number of concurrent transform streams defaults to one.



The **speculum** module exports a function that returns an instance of the `Speculum` class which extends `stream.Transform`. To access the `Speculum` class `require('speculum')`. The **speculum** stream round-robins transformers, constructed by `create`, and exposes their buffers and errors through its `stream.Readable` interface.



## Installation



With [npm](https://npmjs.org/package/speculum), do:



```

$ npm install speculum

```



## License



[MIT License](https://raw.github.com/michaelnisi/speculum/master/LICENSE)