1 # Node Thread Pool :arrow_double_up: :on:
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12 <a href="#installation">Installation</a>
14 <a href="#usage">Usage</a>
16 <a href="#api">API</a>
18 <a href="#cyp">Choose a pool</a>
20 <a href="#contribute">Contribute</a>
22 <a href="#nv">Compatibility</a>
24 <a href="#license">License</a>
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>
35 npm install node-thread-pool --save
37 <h2 id="usage">Usage</h2>
39 You can implement a worker in a simple way , extending the class ThreadWorker :
43 const { ThreadWorker } = require('node-pool')
45 function yourFunction (data) {
46 // this will be executed in the worker thread,
47 // the data will be received by using the execute method
51 class MyWorker extends ThreadWorker {
53 super(yourFunction, { maxInactiveTime: 1000 * 60})
56 module.exports = new MyWorker()
59 Instantiate your pool based on your needed :
63 const { FixedThreadPool, DynamicThreadPool } = require('node-pool')
65 // a fixed thread pool
66 const pool = new FixedThreadPool(15,
68 { errorHandler: (e) => console.error(e), onlineHandler: () => console.log('worker is online') })
70 // or a dynamic thread pool
71 const pool = new DynamicThreadPool(10, 100,
73 { errorHandler: (e) => console.error(e), onlineHandler: () => console.log('worker is online') })
75 pool.emitter.on('FullPool', () => console.log('Pool is full'))
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 => {
85 <strong> See examples folder for more details ( in particular if you want to use a pool for [multiple functions](./examples/multiFunctionExample.js) ).</strong>
87 <h2 id="nv">Node versions</h2>
89 You can use node version 10.x with --experimental-worker flag, or you can use an higher version (i.e 12.x) <br>
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)
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>
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>
113 Destroy method is available on both pool implementations.<br>
114 This method will call the terminate method on each worker.
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.
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>
131 <h2 id="contribute">Contribute</h2>
133 See guidelines [CONTRIBUTING](./.github/CONTRIBUTING.md)
136 <h2 id="license">License</h2>