bthreads
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A worker_threads wrapper for node.js. Provides transparent fallback for
pre-11.7.0 node.js (via child_process) as well as browser web workers.
Browserifiable, webpack-able.
const threads = require('bthreads');
if (threads.isMainThread) {
const worker = new threads.Worker(__filename, {
workerData: 'foo'
});
worker.on('message', console.log);
worker.on('error', console.error);
worker.on('exit', (code) => {
if (code !== 0)
console.error(`Worker stopped with exit code ${code}.`);
});
} else {
threads.parentPort.postMessage(threads.workerData + 'bar');
}
Output (with node@<11.7.0):
$ node --experimental-worker threads.js
foobar
$ node threads.js
foobar
bthreads has 4 backends and a few layers of fallback:
worker_threads - Uses the still experimental worker_threads module in
node.js. Only usable prior to node.js v11.7.0 if --experimental-worker is
passed on the command line.child_process - Leverages the child_process module in node.js to emulate
worker threads.web_workers - Web Workers API (browser only).polyfill - A polyfill for the web workers API.The current backend is exposed as threads.backend. Note that the current
backend can be set with the BTHREADS_BACKEND environment variable.
Some caveats for the child_process backend:
options.workerData probably has a limited size depending on platform (the
maximum size of an environment variable).SharedArrayBuffer does not work and will throw an error if sent.Caveats for the web_workers backend:
options.workerData possibly has a limited size depending on the browser
(the maximum size of options.name).options.eval will create a data URI and execute a new worker from it. When
using a bundler, note that the bundler will not be able to compile the
eval'd code. This means that require will have limited usability
(restricted to only core browserify modules and bthreads itself).options.eval requires that data: be set for the worker-src
Content-Security-Policy. See content-security-policy.com for a guide.close event for MessagePorts only has partial support (if a thread
suddenly terminates, close will not be emitted for any remote ports).
This is because the close event is not yet a part of the standard Web
Worker API. See https://github.com/whatwg/html/issues/1766 for more info.SharedArrayBuffer cannot be sent as workerData.Blob and File may not be able to be cloned when sent as workerData
depending on your Content-Security-Policy.FileList will emerge on the other side as an Array rather than a
FileList when sent as workerData.Caveats for the polyfill backend:
importScripts will perform a synchronous XMLHttpRequest and potentially
freeze the UI. Additionally, XHR is bound to certain cross-origin rules that
importScripts is not.SharedArrayBuffer cannot be sent as workerData.Blob and File may not be able to be cloned when sent as workerData
depending on your Content-Security-Policy.FileList will emerge on the other side as an Array rather than a
FileList when sent as workerData.ArrayBuffers behave as if they were SharedArrayBuffers
(i.e. they're not neutered). Be careful!error events on worker
objects.console object will not be linked to process.{stdout,stderr} when
inside a worker (note: this is fixable if browserify and webpack were to
slightly modify their console module). However, threads.console will work
normally.Caveats for all of the above:
worker.postMessage(Array.prototype)).Finally, caveats for the worker_threads backend:
worker_threads is still experimental in node.js!The low-level node.js API is not very useful on its own. bthreads optionally provides an API similar to bsock.
Example (for brevity, the async wrapper is not included below):
const threads = require('bthreads');
if (threads.isMainThread) {
const thread = new threads.Thread(__filename);
thread.bind('event', (x, y) => {
console.log(x + y);
});
console.log(await thread.call('job', ['hello']));
} else {
const {parent} = threads;
parent.hook('job', async (arg) => {
return arg + ' world';
});
parent.fire('event', ['foo', 'bar']);
}
Output:
foobar
hello world
You may find yourself wanting to parallelize the same worker jobs. The
high-level API offers a thread pool object (threads.Pool) which will
automatically load balance and scale to the number of CPU cores.
if (threads.isMainThread) {
const pool = new threads.Pool(threads.source);
const results = await Promise.all([
pool.call('job1'), // Runs on thread 1.
pool.call('job2'), // Runs on thread 2.
pool.call('job3') // Runs on thread 3.
]);
console.log(results);
} else {
Buffer.poolSize = 1; // Make buffers easily transferrable.
pool.hook('job1', async () => {
const buf = Buffer.from('job1 result');
return [buf, [buf.buffer]]; // Transfer the array buffer.
});
pool.hook('job2', async () => {
return 'job2 result';
});
pool.hook('job3', async () => {
return 'job3 result';
});
}
It's good to be aware of browserify and how it sets __filename and
__dirname.
For example:
const worker = new threads.Worker(`${__dirname}/worker.js`);
If your code resides in /root/project/lib/main.js, the browserify generated
path will ultimately be /lib/worker.js. Meaning /root/project/lib/worker.js
should exist for node and http://[host]/lib/worker.js should exist for the
browser.
The browser backend also exposes a browser flag for this situation.
Example:
const worker = new threads.Worker(threads.browser
? 'http://.../' + path.basename(file)
: file);
To make self-execution easier, bthreads also exposes a threads.source
property which refers to the main module's filename in node.js and the current
script URL in the browser.
In the browser, bthreads exposes a more useful version of importScripts.
const threads = require('bthreads');
const _ = threads.importScripts('https://unpkg.com/underscore/underscore.js');
This should work for any library exposed as UMD or CommonJS. Note that
threads.importScripts behaves more like require in that it caches modules
by URL. The cache is accessible through threads.importScripts.cache.
Note that if you are eval'ing some code inside a script you plan to bundle with
browserify or webpack, require may get unintentionally transformed or
overridden. This generally happens when you are calling toString on a defined
function.
const threads = require('bthreads');
function myWorker() {
const threads = require('bthreads');
threads.parentPort.postMessage('foo');
}
const code = `(${myWorker})();`;
const worker = new threads.Worker(code, { eval: true });
The solution is to access global.require instead of require.
const threads = require('bthreads');
function myWorker() {
const threads = global.require('bthreads');
threads.parentPort.postMessage('foo');
}
const code = `(${myWorker})();`;
const worker = new threads.Worker(code, { eval: true });
threads.isMainThread - See worker_threads documentation.threads.parentPort - See worker_threads documentation (worker only).threads.threadId - See worker_threads documentation.threads.workerData - See worker_threads documentation (worker only).threads.MessagePort - See worker_threads documentation.threads.MessageChannel - See worker_threads documentation.threads.Worker - See worker_threads documentation.threads.backend - A string indicating the current backend
(worker_threads, child_process, web_workers, or polyfill).threads.source - The current main module filename or script URL (null
if in eval'd thread).threads.browser - true if a browser backend is being used.threads.process - Reference to the child_process backend. This is
present to explicitly use the child_process backend instead of the
worker_threads backend.threads.exit(code) - A reference to process.exit.threads.stdin - A reference to process.stdin.threads.stdout - A reference to process.stdout.threads.stderr - A reference to process.stderr.threads.console - A reference to global.console.threads.importScripts(url) - importScripts() wrapper (browser+worker
only).threads.cores - Number of CPU cores available.threads.Thread - Thread Class (see below).threads.Port - Port Class (see below).threads.Channel - Channel Class (see below).threads.Pool - Pool Class (see below).threads.parent - A reference to the parent Port (worker only, see
below).new Socket() - Not meant to be called directly.Socket#events (read only) - A reference to the bind EventEmitter.Socket#bind(name, handler) - Bind remote event.Socket#unbind(name, handler) - Unbind remote event.Socket#hook(name, handler) - Add hook handler.Socket#unhook(name) - Remove hook handler.Socket#send(msg, [transferList]) - Send message, will be emitted as a
message event on the other side.Socket#fire(name, args, [transferList]) - Fire bind event.Socket#call(name, args, [transferList], [timeout]) (async) - Call remote
hook.Socket#hasRef() - Test whether socket has reference.Socket#ref() - Reference socket.Socket#unref() - Clear socket reference.Socket@message(msg) - Emitted on message received.Socket@error(err) - Emitted on error.Socket@event(event, args) - Emitted on bind event.new Thread(filename, [options]) - Instantiate thread with module.new Thread(code, [options]) - Instantiate thread with code.new Thread(function, [options]) - Instantiate thread with function.Thread#stdin (read only) - A writable stream representing stdin (only
present if options.stdin was passed).Thread#stdout (read only) - A readable stream representing stdout.Thread#stderr (read only) - A readable stream representing stderr.Thread#threadId (read only) - An integer representing the thread ID.Thread#terminate([callback]) - Terminate the thread and optionally bind
to the exit event.Thread#close() (async) - Terminate the thread and wait for exit but also
listen for errors and reject the promise if any occur (in other words, a
better async version of Thread#terminate).Thread@online() - Emitted once thread is online.Thread@exit(code) - Emitted on exit.new Port() - Not meant to be called directly.Port#start() - Open and bind port (usually automatic).Port#close() - Close port.Port@close() - Emitted on port close.new Channel() - Instantiate channel.Channel#port1 (read only) - A Port object.Channel#port2 (read only) - A Port object.new Pool(filename, [options]) - Instantiate pool with module.new Pool(code, [options]) - Instantiate pool with code.new Pool(function, [options]) - Instantiate pool with function.Pool#file (read only) - A reference to the filename, function, or code
that was passed in.Pool#options (read only) - A reference to the options passed in.Pool#size (read only) - Number of threads to spawn.Pool#events (read only) - A reference to the bind EventEmitter.Pool#threads (read only) - A Set containing all spawned threads.Pool#open() - Open and populate the pool with this.size threads
(otherwise threads will be lazily spawned).Pool#close() (async) - Close all threads in pool, reject on errors.Pool#next() - Return the next thread in queue (this may spawn a new
thread).Pool#terminate(callback) - Terminate all threads in pool, optionally
execute a callback once exit has been emitted for all threads.Pool#bind(name, handler) - Bind remote event for all threads.Pool#unbind(name, handler) - Unbind remote event for all threads.Pool#hook(name, handler) - Add hook handler for all threads.Pool#unhook(name) - Remove hook handler for all threads.Pool#send(msg) - Send message to all threads, will be emitted as a
message event on the other side (this will populate the pool with threads
on the first call).Pool#fire(name, args) - Fire bind event to all threads (this will
populate the pool with threads on the first call).Pool#call(name, args, [transferList], [timeout]) (async) - Call remote
hook on next thread in queue (this may spawn a new thread).Pool#hasRef() - Test whether pool has reference.Pool#ref() - Reference pool.Pool#unref() - Clear pool reference.Pool@message(msg, thread) - Emitted on message received.Pool@error(err, thread) - Emitted on error.Pool@event(event, args, thread) - Emitted on bind event.Pool@spawn(thread) - Emitted immediately after thread is spawned.Pool@online(thread) - Emitted once thread is online.Pool@exit(code, thread) - Emitted on thread exit.The options object accepted by the Thread, Pool, and Worker classes is
nearly identical to the worker_threads worker options with some differences:
options.type and options.credentials are valid options when using the
browser backend (see web_workers). Note that options.type = 'module' will
not work with the polyfill backend. If a file extension is .mjs,
options.type is automatically set to module for consistency with node.js.require('path') works, for example), as well as bthreads itself.
When using a browser backend options.header is a valid option. It should be
the URL to a bundle. By default, bthreads imports the bthreads-bundle
package from unpkg.com.Pool class accepts size option. This allows you to manually set the
pool size instead of determining it by the number of CPU cores.If you contribute code to this project, you are implicitly allowing your code
to be distributed under the MIT license. You are also implicitly verifying that
all code is your original work. </legalese>
See LICENSE for more info.
FAQs
worker threads for javascript
We found that bthreads demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
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