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1 # Node Thread Pool :arrow_double_up: :on:
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10
11 <h2>Why Poolifier? </h2>
12 Poolifier is used to perform heavy CPU bound tasks on nodejs servers, it implements thread pools ( yes, more thread pool implementations, so you can choose which one fit better for you ) using <a href="https://nodejs.org/api/worker_threads.html#worker_threads_worker_threads">worker-threads </a>.<br>
13 With poolifier you can improve your <strong>performance</strong> and resolve problems related to the event loop.<br>
14 Moreover you can execute your CPU tasks using an API designed to improve the <strong>developer experience</strong>.
15
16
17
18 <h2>Contents </h2>
19 <h3 align="center">
20 <a href="#installation">Installation</a>
21 <span> · </span>
22 <a href="#usage">Usage</a>
23 <span> · </span>
24 <a href="#api">API</a>
25 <span> · </span>
26 <a href="#cyp">Choose a pool</a>
27 <span> · </span>
28 <a href="#contribute">Contribute</a>
29 <span> · </span>
30 <a href="#nv">Compatibility</a>
31 <span> · </span>
32 <a href="#license">License</a>
33 </h3>
34
35 <h2> Overview </h2>
36 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>
37 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>
38 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>
39 You have to implement your worker extending the ThreadWorker class<br>
40 <h2 id="installation">Installation</h2>
41
42 ```
43 npm install poolifier --save
44 ```
45 <h2 id="usage">Usage</h2>
46
47 You can implement a worker in a simple way , extending the class ThreadWorker :
48
49 ```js
50 'use strict'
51 const { ThreadWorker } = require('poolifier')
52
53 function yourFunction (data) {
54 // this will be executed in the worker thread,
55 // the data will be received by using the execute method
56 return { ok: 1 }
57 }
58
59 module.exports = new ThreadWorker(yourFunction, { maxInactiveTime: 60000, async: false })
60 ```
61
62 Instantiate your pool based on your needed :
63
64 ```js
65 'use strict'
66 const { FixedThreadPool, DynamicThreadPool } = require('poolifier')
67
68 // a fixed thread pool
69 const pool = new FixedThreadPool(15,
70 './yourWorker.js',
71 { errorHandler: (e) => console.error(e), onlineHandler: () => console.log('worker is online') })
72
73 // or a dynamic thread pool
74 const pool = new DynamicThreadPool(10, 100,
75 './yourWorker.js',
76 { errorHandler: (e) => console.error(e), onlineHandler: () => console.log('worker is online') })
77
78 pool.emitter.on('FullPool', () => console.log('Pool is full'))
79
80 // the execute method signature is the same for both implementations,
81 // so you can easy switch from one to another
82 pool.execute({}).then(res => {
83 console.log(res)
84 }).catch ....
85
86 ```
87
88 <strong> See examples folder for more details ( in particular if you want to use a pool for [multiple functions](./examples/multiFunctionExample.js) ).</strong>
89
90 <h2 id="nv">Node versions</h2>
91
92 You can use node versions 12.x , 13.x, 14.x <br>
93
94 <h2 id="api">API</h2>
95
96 ### `pool = new FixedThreadPool(numThreads, filePath, opts)`
97 `numThreads` (mandatory) Num of threads for this worker pool <br>
98 `filePath` (mandatory) Path to a file with a worker implementation <br>
99 `opts` (optional) An object with these properties :
100 - `errorHandler` - A function that will listen for error event on each worker thread
101 - `onlineHandler` - A function that will listen for online event on each worker thread
102 - `exitHandler` - A function that will listen for exit event on each worker thread
103 - `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)
104
105 ### `pool = new DynamicThreadPool(min, max, filePath, opts)`
106 `min` (mandatory) Same as FixedThreadPool numThreads , this number of threads will be always active <br>
107 `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>
108 `filePath` (mandatory) Same as FixedThreadPool <br>
109 `opts` (optional) Same as FixedThreadPool <br>
110
111 ### `pool.execute(data)`
112 Execute method is available on both pool implementations ( return type : Promise): <br>
113 `data` (mandatory) An object that you want to pass to your worker implementation <br>
114
115 ### `pool.destroy()`
116 Destroy method is available on both pool implementations.<br>
117 This method will call the terminate method on each worker.
118
119
120 ### `class YourWorker extends ThreadWorker`
121 `fn` (mandatory) The function that you want to execute on the worker thread <br>
122 `opts` (optional) An object with these properties :
123 - `maxInactiveTime` - Max time to wait tasks to work on ( in ms) , after this period the new worker threads will die.
124 - `async` - true/false , true if your function contains async pieces else false
125
126 <h2 id="cyp">Choose your pool</h2>
127 Performance is one of the main target of these thread pool implementations, we want to have a strong focus on this.<br>
128 We already have a bench folder where you can find some comparisons.
129 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>
130 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>
131 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>
132 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>
133 But in general , <strong>always profile your application </strong>
134
135 <h2 id="contribute">Contribute</h2>
136
137 See guidelines [CONTRIBUTING](CONTRIBUTING.md) <br>
138 Choose your task here <a href="https://github.com/pioardi/poolifier/projects/1"> 2.0.0</a>, propose an idea, a fix, an improvement. <br>
139
140
141 <h2 id="license">License</h2>
142
143 [MIT](./LICENSE)