javascriptAsync race conditionHard

Expensive database queries duplicating

Time: 0:00

What it should do

countLoads(n) makes n concurrent calls to a cached loader and returns how many times the expensive load actually ran. It should always be 1.

What goes wrong

countLoads(3) returns 3 — the cache does nothing when the calls overlap, though countLoads(1) correctly returns 1.

Hints

This is an async and race conditions bug

A missing await, results in the wrong order, and updates that overwrite each other under load.