Node.js Worker Threads

Node:worker_threads Module

• Enables the use of threads that execute JavaScript in parallel for CPU-intensive operations.
• Does not help with I/O-intensive work, as Node.js built-in asynchronous I/O operations are more efficient.
• Allows threads to share memory by transferring ArrayBuffer instances or sharing SharedArrayBuffer instances.

Worker Threads

• Useful for performing CPU-intensive JavaScript operations.
• Can be spawned for each task, but a pool of Workers is recommended to avoid overhead.
• Inherit non-process-specific options by default, but can be customized using Worker constructor options.

Worker Thread Pool

• Use the AsyncResource API to inform diagnostic tools about the correlation between tasks and their outcomes.
• Implementing a worker pool provides asynchronous stack traces.

markAsUntransferable() Method

• Marks an object as not transferable, throwing an error if it's in the transfer list of a port.postMessage() call.
• No-op if the object is a primitive value.
• Use for objects that can be cloned, rather than transferred, and are used by other objects on the sending side.

MessagePort Class

• Represents one end of an asynchronous, two-way communications channel.
• Can be used to transfer structured data, memory regions, and other MessagePorts between different Workers.
• Inherits from EventTarget rather than EventType (as of v14.7.0).

MessagePort Events

'close' Event

• Emitted once either side of the channel has been disconnected.
• Fired when a port is closed.

'message' Event

• Emitted for any incoming message, containing the cloned input of port.postMessage().
• Listeners receive a clone of the value parameter as passed to postMessage().

'messageerror' Event

• Emitted when deserializing a message failed.
• Usually occurs when there's an error instantiating the posted JS object on the receiving end.

port.close() Method

• Disables further sending of messages on either side of the connection.
• Emits the 'close' event on both MessagePort instances that are part of the channel.

port.postMessage() Method

• Sends a message with an optional transfer list.
• Throws an error if an untransferable object is in the transfer list (as of v21.0.0).