README.MD

   1 # Node Thread Pool :arrow_double_up: :on:
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   9
  10 <h2>Contents </h2>
  11 <h3 align="center">
  12   <a href="#installation">Installation</a>
  13   <span> · </span>
  14   <a href="#usage">Usage</a>
  15   <span> · </span>
  16   <a href="#api">API</a>
  17   <span> · </span>
  18   <a href="#cyp">Choose a pool</a>
  19   <span> · </span>
  20   <a href="#contribute">Contribute</a>
  21   <span> · </span>
  22   <a href="#nv">Compatibility</a>
  23   <span> · </span>
  24   <a href="#license">License</a>
  25 </h3>
  26
  27 <h2> Overview </h2>
  28 Node pool contains two <a href="https://nodejs.org/api/worker_threads.html#worker_threads_worker_threads">worker-threads </a> pool implementations , you don' t have to deal with worker-threads complexity. <br>
  29 The first implementation is a static thread pool , with a defined number of threads that are started at creation time and will be reused.<br>
  30 The second implementation is a dynamic thread pool with a number of threads started at creation time ( these threads will be always active and reused) and other threads created when the load will increase ( with an upper limit, these threads will be reused when active ), the new created threads will be stopped after a configurable period of inactivity. <br>
  31 You have to implement your worker extending the ThreadWorker class<br>
  32 <h2 id="installation">Installation</h2>
  33
  34 ```
  35 npm install node-thread-pool --save
  36 ```
  37 <h2 id="usage">Usage</h2>
  38
  39 You can implement a worker in a simple way , extending the class ThreadWorker :
  40
  41 ```js
  42 'use strict'
  43 const { ThreadWorker } = require('node-pool')
  44
  45 function yourFunction (data) {
  46   // this will be executed in the worker thread,
  47   // the data will be received by using the execute method
  48   return { ok: 1 }
  49 }
  50
  51 class MyWorker extends ThreadWorker {
  52   constructor () {
  53     super(yourFunction, { maxInactiveTime: 1000 * 60})
  54   }
  55 }
  56 module.exports = new MyWorker()
  57 ```
  58
  59 Instantiate your pool based on your needed :
  60
  61 ```js
  62 'use strict'
  63 const { FixedThreadPool, DynamicThreadPool } = require('node-pool')
  64
  65 // a fixed thread pool
  66 const pool = new FixedThreadPool(15,
  67   './yourWorker.js',
  68   { errorHandler: (e) => console.error(e), onlineHandler: () => console.log('worker is online') })
  69
  70 // or a dynamic thread pool
  71 const pool = new DynamicThreadPool(10, 100,
  72   './yourWorker.js',
  73   { errorHandler: (e) => console.error(e), onlineHandler: () => console.log('worker is online') })
  74
  75 pool.emitter.on('FullPool', () => console.log('Pool is full'))
  76
  77 // the execute method signature is the same for both implementations,
  78 // so you can easy switch from one to another
  79 pool.execute({}).then(res => {
  80   console.log(res)
  81 }).catch ....
  82
  83 ```
  84
  85 <strong> See examples folder for more details ( in particular if you want to use a pool for [multiple functions](./examples/multiFunctionExample.js) ).</strong>
  86
  87 <h2 id="nv">Node versions</h2>
  88
  89 You can use node version  10.x  with --experimental-worker flag, or you can use an higher version (i.e 12.x) <br>
  90
  91 <h2 id="api">API</h2>
  92
  93 ### `pool = new FixedThreadPool(numThreads, filePath, opts)`
  94 `numThreads` (mandatory) Num of threads for this worker pool <br>
  95 `filePath` (mandatory) Path to a file with a worker implementation <br>
  96 `opts` (optional) An object with these properties :
  97 - `errorHandler` - A function that will listen for error event on each worker thread
  98 - `onlineHandler` - A function that will listen for online event on each worker thread
  99 - `exitHandler` - A function that will listen for exit event on each worker thread
 100 - `maxTasks` - This is just to avoid not useful warnings message, is used to set <a href="https://nodejs.org/dist/latest-v12.x/docs/api/events.html#events_emitter_setmaxlisteners_n">maxListeners</a> on event emitters ( workers are event emitters)
 101
 102 ### `pool = new DynamicThreadPool(min, max, filePath, opts)`
 103 `min` (mandatory) Same as FixedThreadPool numThreads , this number of threads will be always active <br>
 104 `max` (mandatory) Max number of workers that this pool can contain, the new created threads will die after a threshold ( default is 1 minute , you can override it in your worker implementation). <br>
 105 `filePath` (mandatory) Same as FixedThreadPool  <br>
 106 `opts` (optional) Same as FixedThreadPool <br>
 107
 108 ### `pool.execute(data)`
 109 Execute method is available on both pool implementations ( return type : Promise): <br>
 110 `data` (mandatory) An object that you want to pass to your worker implementation <br>
 111
 112 ### `pool.destroy()`
 113 Destroy method is available on both pool implementations.<br>
 114 This method will call the terminate method on each worker.
 115
 116
 117 ### `class YourWorker extends ThreadWorker`
 118 `fn` (mandatory) The function that you want to execute on the worker thread <br>
 119 `opts` (optional) An object with these properties :
 120 - `maxInactiveTime` - Max time to wait tasks to work on ( in ms) , after this period the new worker threads will die.
 121
 122 <h2 id="cyp">Choose your pool</h2>
 123 Performance is one of the main target of these thread pool implementations, we want to have a strong focus on this.<br>
 124 We already have a bench folder where you can find some comparisons.
 125 To choose your pool consider that with a FixedThreadPool or a DynamicThreadPool ( in this case is important the min parameter passed to the constructor) your application memory footprint will increase . <br>
 126 Increasing the memory footprint, your application will be ready to accept more CPU bound tasks, but during idle time your application will consume more memory. <br>
 127 One good choose from my point of view is to profile your application using Fixed/Dynamic thread pool , and to see your application metrics when you increase/decrease the num of threads. <br>
 128 For example you could keep the memory footprint low choosing a DynamicThreadPool with 5 threads, and allow to create new threads until 50/100 when needed, this is the advantage to use the DynamicThreadPool. <br>
 129 But in general , <strong>always profile your application </strong>
 130
 131 <h2 id="contribute">Contribute</h2>
 132
 133 See guidelines [CONTRIBUTING](./.github/CONTRIBUTING.md)
 134
 135
 136 <h2 id="license">License</h2>
 137
 138 [MIT](./LICENSE)
 139