What's the actual use of the Atomics object in ECMAScript?

Question

The ECMAScript specification defines the Atomics object in the section 24.4.

Among all the global objects this is the more obscure for

Answer 1

Atomics are for synchronising WebWorkers that share memory. They cause memory access into a SharedArrayBuffer to be done in a thread safe way. Shared memory makes multithreading much more useful because:

• It's not necessary to copy data to pass it to threads
• Threads can communicate without using the event loop
• Threads can communicate much faster

Example:

var arr = new SharedArrayBuffer(1024);

// send a reference to the memory to any number of webworkers
workers.forEach(worker => worker.postMessage(arr));

// Normally, simultaneous access to the memory from multiple threads 
// (where at least one access is a write)
// is not safe, but the Atomics methods are thread-safe.
// This adds 2 to element 0 of arr.
Atomics.add(arr, 0, 2)

SharedArrayBuffer was enabled previously on major browsers, but after the Spectre incident it was disabled because shared memory allows implementation of nanosecond-precision timers, which allow exploitation of spectre.

In order to make it safe, browsers need to run pages a separate process for each domain. Chrome started doing this in version 67 and shared memory was re-enabled in version 68.