Browser & Web Performance · Senior · Question 2 of 75

Why did browsers disable `SharedArrayBuffer` by default and then re-enable it only for cross-origin isolated pages?

✓Correct answer: It enables high-resolution timers useful for Spectre attacks; isolation ensures no cross-origin data shares the process
2It was too slow on mobile devices
3It conflicted with service workers

Explanation

With COOP and COEP the page can't pull in cross-origin resources that haven't opted in, so a Spectre gadget has nothing secret to read.

Further reading

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