SharedArrayBuffer

SharedArrayBuffer is a JavaScript object that represents a fixed-length raw binary data buffer whose contents can be shared between workers and the main thread. It enables parallel algorithms by providing a single memory region that can be accessed by multiple execution contexts through typed array views such as Int32Array or Float64Array. This contrasts with ArrayBuffer, where ownership and copies occur when transferring between contexts.

Creating and sharing: You create sab = new SharedArrayBuffer(1024); const view = new Int32Array(sab); To share, send sab to a worker via postMessage; in the worker, construct a corresponding Int32Array view from the same sab. All reads and writes go through the shared memory; use Atomics for synchronization.

Synchronization: Atomic operations on shared memory are performed via the Atomics object: Atomics.store(view, idx, value); Atomics.load(view, idx); Atomics.add(view, idx, value); Atomics.wait and Atomics.notify allow blocking and waking worker threads.

Security and deployment: Access to SharedArrayBuffer was restricted after Spectre vulnerabilities; browsers require cross-origin isolation. Servers must configure Cross-Origin-Opener-Policy: same-origin and Cross-Origin-Embedder-Policy: require-corp. Without this, SharedArrayBuffer usage can be blocked or limited. The requirement helps prevent cross-origin data leakage in shared memory scenarios.

Relation to WebAssembly: SharedArrayBuffer is used to share memory for WebAssembly threads (workers) and for high-performance data processing, enabling multi-threaded execution in Wasm modules.

History and status: SharedArrayBuffer was introduced as a memory-sharing primitive in the JavaScript platform and became widely usable after cross-origin isolation policies were adopted by major browsers. It remains a core tool for parallel JavaScript and Wasm workloads, with browser compatibility varying by environment.