SharedArrayBuffer

Learn shared memory with SharedArrayBuffer.

SharedArrayBuffer

SharedArrayBuffer is a block of memory shared between threads. postMessage copies data; SharedArrayBuffer shares the same memory directly. This removes the copy cost for large data.

When you create a SharedArrayBuffer and send it via postMessage, both sides read and write the same memory. To prevent concurrent write races you use the Atomics object. This is a powerful tool for low-level parallel programming.

Safe access with Atomics

Multiple threads can write to shared memory at the same time; this causes race conditions. The Atomics object provides safe read-write and synchronization primitives.

For example Atomics.store(arr, index, value) does an atomic write; Atomics.load(arr, index) does an atomic read. There are also Atomics.add, Atomics.compareExchange and more. These are the foundation of lock-free programming.

Exercise Log the byteLength value

Create a SharedArrayBuffer of 8 bytes. Log sab.byteLength.

Show example solution

const sab = new SharedArrayBuffer(8);
console.log(sab.byteLength);

Test yourself

Complete the class name

const sab = new ____(8)

Show answer

const sab = new SharedArrayBuffer(8)

Match each piece to its role

SharedArrayBuffer

Shared memory
Atomics

Safe access
sab.byteLength

Byte size
new SharedArrayBuffer(8)

8 bytes
What does SharedArrayBuffer provide?
- A new child process
- A network connection
- Memory shared between threads
- File system access
Show answer

Memory shared between threads — SharedArrayBuffer provides shared memory between threads.

Next lesson: Summary - Worker threads

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