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workerpool
Advanced tools
Package description
The workerpool npm package is a robust solution for offloading CPU intensive tasks to worker threads. It allows you to create a pool of workers and manage the execution of tasks in parallel, which can significantly improve the performance of Node.js applications that need to handle heavy computational work.
Creating a worker pool and executing tasks
This code sample demonstrates how to create a pool of workers and execute a simple 'add' function in a worker thread. The 'exec' method is used to send the task to an available worker and returns a promise that resolves with the result.
const workerpool = require('workerpool');
const pool = workerpool.pool();
function add(a, b) {
return a + b;
}
pool.exec(add, [5, 7])
.then(function (result) {
console.log('Result: ' + result); // prints 12
})
.catch(function (err) {
console.error(err);
})
.then(function () {
pool.terminate(); // terminate all workers when done
});
Using a worker script
This code sample shows how to use a separate worker script file. The 'pool' method is given the path to a worker script, and the 'exec' method is used to call a specific exported function from that script, passing in any necessary arguments.
const workerpool = require('workerpool');
const pool = workerpool.pool(__dirname + '/myWorker.js');
pool.exec('heavyComputation', [largeDataSet])
.then(function (result) {
console.log('Computation result: ' + result);
})
.catch(function (err) {
console.error(err);
})
.then(function () {
pool.terminate();
});
Handling timeouts
This code sample illustrates how to handle task timeouts. The 'exec' method accepts an options object where you can specify a 'timeout' in milliseconds. If the task does not complete within the specified time, the promise is rejected.
const workerpool = require('workerpool');
const pool = workerpool.pool();
pool.exec('longRunningTask', [inputData], { timeout: 10000 })
.then(function (result) {
console.log('Task result: ' + result);
})
.catch(function (err) {
console.error('Task timed out or other error:', err);
})
.then(function () {
pool.terminate();
});
The 'threads' package is similar to workerpool and offers a high-level abstraction for working with Web Workers or Node's Worker Threads. It provides an easy-to-use API for spawning new threads and communication between them. Compared to workerpool, it might offer a more modern API and better integration with ES modules.
Bottleneck is a rate limiter that can be used to throttle function calls. While it does not provide worker threads functionality, it is similar in the sense that it helps manage resource-intensive tasks by controlling how often they are executed. It is more focused on rate limiting rather than parallel execution.
Bull is a Node.js library that implements a fast and robust queue system based on Redis. Although it is not a direct alternative to workerpool, as it is more about job scheduling and processing, it can be used to distribute tasks across multiple processes or servers, which can be seen as a form of parallel processing.
Changelog
2021-06-17, version 2.3.4
Readme
JavaScript is based upon a single event loop which handles one event at a time. Jeremy Epstein explains this clearly:
In Node.js everything runs in parallel, except your code. What this means is that all I/O code that you write in Node.js is non-blocking, while (conversely) all non-I/O code that you write in Node.js is blocking.
This means that CPU heavy tasks will block other tasks from being executed. In case of a browser environment, the browser will not react to user events like a mouse click while executing a CPU intensive task (the browser "hangs"). In case of a node.js server, the server will not respond to any new request while executing a single, heavy request.
For front-end processes, this is not a desired situation. Therefore, CPU intensive tasks should be offloaded from the main event loop onto dedicated workers. In a browser environment, Web Workers can be used. In node.js, child processes are available. An application should be split in separate, decoupled parts, which can run independent of each other in a parallelized way. Effectively, this results in an architecture which achieves concurrency by means of isolated processes and message passing.
workerpool offers an easy way to create a pool of workers for both dynamically offloading computations as well as managing a pool of dedicated workers. workerpool basically implements a thread pool pattern. There is a pool of workers to execute tasks. New tasks are put in a queue. A worker executes one task at a time, and once finished, picks a new task from the queue. Workers can be accessed via a natural, promise based proxy, as if they are available straight in the main application.
workerpool runs on node.js, Chrome, Firefox, Opera, Safari, and IE10+.
Install via npm:
npm install workerpool
To load workerpool in a node.js application (both main application as well as workers):
var workerpool = require('workerpool');
To load workerpool in the browser:
<script src="workerpool.js"></script>
To load workerpool in a web worker in the browser:
importScripts('workerpool.js');
In the following example there is a function add
, which is offloaded dynamically to a worker to be executed for a given set of arguments.
myApp.js
var workerpool = require('workerpool');
var pool = workerpool.pool();
function add(a, b) {
return a + b;
}
pool.exec(add, [3, 4])
.then(function (result) {
console.log('result', result); // outputs 7
})
.catch(function (err) {
console.error(err);
})
.then(function () {
pool.terminate(); // terminate all workers when done
});
Note that both function and arguments must be static and stringifiable, as they need to be send to the worker in a serialized form. In case of large functions or function arguments, the overhead of sending the data to the worker can be significant.
A dedicated worker can be created in a separate script, and then used via a worker pool.
myWorker.js
var workerpool = require('workerpool');
// a deliberately inefficient implementation of the fibonacci sequence
function fibonacci(n) {
if (n < 2) return n;
return fibonacci(n - 2) + fibonacci(n - 1);
}
// create a worker and register public functions
workerpool.worker({
fibonacci: fibonacci
});
This worker can be used by a worker pool:
myApp.js
var workerpool = require('workerpool');
// create a worker pool using an external worker script
var pool = workerpool.pool(__dirname + '/myWorker.js');
// run registered functions on the worker via exec
pool.exec('fibonacci', [10])
.then(function (result) {
console.log('Result: ' + result); // outputs 55
})
.catch(function (err) {
console.error(err);
})
.then(function () {
pool.terminate(); // terminate all workers when done
});
// or run registered functions on the worker via a proxy:
pool.proxy()
.then(function (worker) {
return worker.fibonacci(10);
})
.then(function (result) {
console.log('Result: ' + result); // outputs 55
})
.catch(function (err) {
console.error(err);
})
.then(function () {
pool.terminate(); // terminate all workers when done
});
Worker can also initialize asynchronously:
myAsyncWorker.js
define(['workerpool/dist/workerpool'], function(workerpool) {
// a deliberately inefficient implementation of the fibonacci sequence
function fibonacci(n) {
if (n < 2) return n;
return fibonacci(n - 2) + fibonacci(n - 1);
}
// create a worker and register public functions
workerpool.worker({
fibonacci: fibonacci
});
});
Examples are available in the examples directory:
https://github.com/josdejong/workerpool/tree/master/examples
The API of workerpool consists of two parts: a function workerpool.pool
to create a worker pool, and a function workerpool.worker
to create a worker.
A workerpool can be created using the function workerpool.pool
:
workerpool.pool([script: string] [, options: Object]) : Pool
When a script
argument is provided, the provided script will be started as a dedicated worker.
When no script
argument is provided, a default worker is started which can be used to offload functions dynamically via Pool.exec
.
Note that on node.js, script
must be an absolute file path like __dirname + '/myWorker.js'
.
The following options are available:
minWorkers: number | 'max'
. The minimum number of workers that must be initialized and kept available. Setting this to 'max'
will create maxWorkers
default workers (see below).maxWorkers: number
. The default number of maxWorkers is the number of CPU's minus one. When the number of CPU's could not be determined (for example in older browsers), maxWorkers
is set to 3.A worker pool contains the following functions:
Pool.exec(method: Function | string, params: Array | null) : Promise.<*, Error>
Execute a function on a worker with given arguments.
method
is a string, a method with this name must exist at the worker and must be registered to make it accessible via the pool. The function will be executed on the worker with given parameters.method
is a function, the provided function fn
will be stringified, send to the worker, and executed there with the provided parameters. The provided function must be static, it must not depend on variables in a surrounding scope.Pool.proxy() : Promise.<Object, Error>
Create a proxy for the worker pool. The proxy contains a proxy for all methods available on the worker. All methods return promises resolving the methods result.
Pool.stats() : Object
Retrieve statistics on workers, and active and pending tasks.
Returns an object containing the following properties:
{
totalWorkers: 0,
busyWorkers: 0,
idleWorkers: 0,
pendingTasks: 0,
activeTasks: 0
}
Pool.terminate([force: boolean [, timeout: number]])
If parameter force
is false (default), workers will finish the tasks they are working on before terminating themselves. When force
is true, all workers are terminated immediately without finishing running tasks. If timeout
is provided, worker will be forced to terminal when the timeout expires and the worker has not finished.
Pool.clear([force: boolean])
Deprecated: use Pool.terminate
instead
.
Clear all workers from the pool. If parameter force
is false (default), workers will finish the tasks they are working on before terminating themselves. When force
is true, all workers are terminated immediately without finishing running tasks.
The function Pool.exec
and the proxy functions all return a Promise
. The promise has the following functions available:
Promise.then(fn: Function.<result: *>)
Promise.catch(fn: Function.<error: Error>)
Promise.cancel()
Promise.CancellationError
.Promise.timeout(delay: number)
Promise.TimeoutError
.Example usage:
var workerpool = require('workerpool');
function add(a, b) {
return a + b;
}
var pool1 = workerpool.pool();
// offload a function to a worker
pool1.exec(add, [2, 4])
.then(function (result) {
console.log(result); // will output 6
})
.catch(function (err) {
console.error(err);
});
// create a dedicated worker
var pool2 = workerpool.pool(__dirname + '/myWorker.js');
// supposed myWorker.js contains a function 'fibonacci'
pool2.exec('fibonacci', [10])
.then(function (result) {
console.log(result); // will output 55
})
.catch(function (err) {
console.error(err);
});
// create a proxy to myWorker.js
pool2.proxy()
.then(function (myWorker) {
return myWorker.fibonacci(10)
})
.then(function (result) {
console.log(result); // will output 55
})
.catch(function (err) {
console.error(err);
});
// create a pool with a specified maximum number of workers
var pool3 = workerpool.pool({maxWorkers: 7});
A worker is constructed as:
workerpool.worker([methods: Object.<String, Function>])
Argument methods
is optional can can be an object with functions available in the worker. Registered functions will be available via the worker pool.
Example usage:
// file myWorker.js
var workerpool = require('workerpool');
function add(a, b) {
return a + b;
}
function multiply(a, b) {
return a * b;
}
// create a worker and register functions
workerpool.worker({
add: add,
multiply: multiply
});
Asynchronous results can be handled by returning a Promise from a function in the worker:
// file myWorker.js
var workerpool = require('workerpool');
function timeout(delay) {
return new Promise(function (resolve, reject) {
setTimeout(resolve, delay)
});
}
// create a worker and register functions
workerpool.worker({
timeout: timeout
});
Following properties are available for convenience:
map
, reduce
, forEach
,
filter
, some
, every
, ...First clone the project from github:
git clone git://github.com/josdejong/workerpool.git
cd workerpool
Install the project dependencies:
npm install
Then, the project can be build by executing the build script via npm:
npm run build
This will build the library workerpool.js and workerpool.min.js from the source files and put them in the folder dist.
To execute tests for the library, install the project dependencies once:
npm install
Then, the tests can be executed:
npm test
To test code coverage of the tests:
npm run coverage
To see the coverage results, open the generated report in your browser:
./coverage/lcov-report/index.html
Copyright (C) 2014-2018 Jos de Jong wjosdejong@gmail.com
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
FAQs
Offload tasks to a pool of workers on node.js and in the browser
The npm package workerpool receives a total of 6,091,182 weekly downloads. As such, workerpool popularity was classified as popular.
We found that workerpool demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 0 open source maintainers collaborating on the project.
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