README.MD

   1 # Node Thread Pool :arrow_double_up: :on:
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   7
   8 <h2>Contents </h2>
   9 <h3 align="center">
  10   <a href="#installation">Installation</a>
  11   <span> · </span>
  12   <a href="#usage">Usage</a>
  13   <span> · </span>
  14   <a href="#api">API</a>
  15   <span> · </span>
  16   <a href="#cyp">Choose a pool</a>
  17   <span> · </span>
  18   <a href="#contribute">Contribute</a>
  19   <span> · </span>
  20   <a href="#nv">Compatibility</a>
  21   <span> · </span>
  22   <a href="#license">License</a>
  23 </h3>
  24
  25 <h2> Overview </h2>
  26 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>
  27 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>
  28 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 ), the new created threads will be stopped after a configurable period of inactivity. <br>
  29 You have to implement your worker extending the ThreadWorker class<br>
  30 <h2 id="installation">Installation</h2>
  31
  32 ```
  33 npm install node-thread-pool --save
  34 ```
  35 <h2 id="usage">Usage</h2>
  36
  37 You can implement a worker in a simple way , extending the class ThreadWorker :
  38
  39 ```js
  40 'use strict'
  41 const { ThreadWorker } = require('node-pool')
  42
  43 class MyWorker extends ThreadWorker {
  44   constructor () {
  45     super((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     }, { maxInactiveTime: 1000 * 60})
  50   }
  51 }
  52 module.exports = new MyWorker()
  53 ```
  54
  55 Instantiate your pool based on your needed :
  56
  57 ```js
  58 'use strict'
  59 const { FixedThreadPool, DynamicThreadPool } = require('node-pool')
  60
  61 // a fixed thread pool
  62 const pool = new FixedThreadPool(15,
  63   './yourWorker.js')
  64
  65 // or a dynamic thread pool
  66 const pool = new DynamicThreadPool(10, 100,
  67   './yourWorker.js')
  68 pool.emitter.on('FullPool', () => console.log('Pool is full'))
  69
  70 // the execute method signature is the same for both implementations,
  71 // so you can easy switch from one to another
  72 pool.execute({}).then(res => {
  73   console.log(res)
  74 }).catch ....
  75
  76 ```
  77
  78 <strong> See examples folder for more details.</strong>
  79
  80 <h2 id="nv">Node versions</h2>
  81
  82 You can use node version  10.x  with --experimental-worker flag, or you can use an higher version (i.e 12.x) <br>
  83
  84 <h2 id="api">API</h2>
  85
  86 ### `pool = new FixedThreadPool(numThreads, filePath, opts)`
  87 `numThreads` (mandatory) Num of threads for this worker pool <br>
  88 `filePath` (mandatory) Path to a file with a worker implementation <br>
  89 `opts` (optional) An object with these properties :
  90 - `errorHandler` - A function that will listen for error event on each worker thread
  91 - `onlineHandler` - A function that will listen for online event on each worker thread
  92 - `exitHandler` - A function that will listen for exit event on each worker thread
  93 - `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)
  94
  95 ### `pool = new DynamicThreadPool(min, max, filePath, opts)`
  96 `min` (mandatory) Same as FixedThreadPool numThreads , this number of threads will be always active <br>
  97 `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>
  98 `filePath` (mandatory) Same as FixedThreadPool  <br>
  99 `opts` (optional) Same as FixedThreadPool <br>
 100
 101 ### `pool.execute(data)`
 102 Execute method is available on both pool implementations ( return type : Promise): <br>
 103 `data` (mandatory) An object that you want to pass to your worker implementation <br>
 104
 105 ### `pool.destroy()`
 106 Destroy method is available on both pool implementations.<br>
 107 This method will call the terminate method on each worker.
 108
 109
 110 ### `class YourWorker extends ThreadWorker`
 111 `fn` (mandatory) The function that you want to execute on the worker thread <br>
 112 `opts` (optional) An object with these properties :
 113 - `maxInactiveTime` - Max time to wait tasks to work on ( in ms) , after this period the new worker threads will die.
 114
 115 <h2 id="cyp">Choose your pool</h2>
 116 Performance is one of the main target of these thread pool implementation, we want to have a strong focus on this.<br>
 117 We already have a bench folder where you can find some comparisons.
 118 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>
 119 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>
 120 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>
 121 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 requests, this is the advantage to use the DynamicThreadPool. <br>
 122 But in general , <strong>always profile your application </strong>
 123
 124 <h2 id="contribute">Contribute</h2>
 125
 126 See guidelines [CONTRIBUTING](./.github/CONTRIBUTING.md)
 127
 128
 129 <h2 id="license">License</h2>
 130
 131 [MIT](./LICENSE)
 132