Shared memory isolation
checking
demo · v133
Real spinlock in two Workers
The TC39 proposal motivates Atomics.pause() with a thread spin-waiting on shared memory. This page runs the real shape: one producer Worker flips a SharedArrayBuffer flag on a timer while one consumer Worker spins on that flag, once tightly and once with Atomics.pause().
Atomics.pause in worker
checking
SharedArrayBuffer is unavailable here, so this page cannot run the real producer/consumer spinlock. The controls stay visible, but the run button is disabled rather than pretending to measure a single-thread loop.
plain tight spin
—empty flag probes—
validated handoffs—
checksum—
spin with Atomics.pause()
—empty flag probes—
validated handoffs—
checksum—
Run the benchmark to compare wall time and how many times the consumer observed an empty flag.
the pattern
The producer waits for the shared flag to return to 0, waits on its own timer, writes the next value, then stores 1. The consumer runs on a separate Worker and spins until it sees 1. The only difference between the two measured runs is whether the consumer calls Atomics.pause() while the flag is still empty.
// Consumer Worker
while (Atomics.load(cells, FLAG) !== READY) {
emptyChecks++;
if (usePause) Atomics.pause(1 + (emptyChecks & 31));
}
const value = Atomics.load(cells, VALUE);
Atomics.store(cells, FLAG, EMPTY);
Atomics.notify(cells, FLAG, 1);The proposal says the method is a spin-wait hint with no observable behavior other than timing, so this demo reports both elapsed time and the count of empty probes to make the wait visible.