How do 'cluster' and 'worker_threads' work in Node.js?

Question

• Did I understand correctly: If I use cluster package, does it mean that a new node instance is created for each created worker?

• What is the difference between cluster and worker_threads packages?

Greggrega

Answer 1

Effectively what you are differing is process based vs thread based. Threads share memory (e.g. SharedArrayBuffer) whereas processes don't. Essentially they are the same thing categorically.

cluster

• One process is launched on each CPU and can communicate via IPC.
• Each process has it's own memory with it's own Node (v8) instance. Creating tons of them may create memory issues.
• Great for spawning many HTTP servers that share the same port b/c the master main process will multiplex the requests to the child processes.

worker threads

• One process total
• Creates multiple threads with each thread having one Node instance (one event loop, one JS engine). Most Node API's are available to each thread except a few. So essentially Node is embedding itself and creating a new thread.
• Shares memory with other threads (e.g. SharedArrayBuffer)
• Great for CPU intensive tasks like processing data or accessing the file system. Because NodeJS is single threaded, synchronous tasks can be made more efficient with workers

Longheaded

For worker_threads: One process total. Does that mean spread across multiple V8 instances ? – Ivoryivorywhite

Each worker thread will have it's own V8 instance and Event Loop. This is how you gain parallelism. They call it a V8 isolate. Effectively, this is an independent instance of the V8 runtime that has its own JS heap and a microtask queue. Each Node.js worker thread can thus run it's code in isolation without sharing their heaps. Communication; however, occurs through a message channel between child and parent. – Longheaded

@Longheaded Wouldn't worker threads involve in deadlock situations as they share memory? If yes, then wouldn't it slow down the CPU performance? – Heal

Why do you strikethrough master ? – Trophozoite

@SarimJavaidKhan They do not share memory. data passed over channels is copied, but this is still way more efficient than JSON stringify/parse for IPC. – Ictinus