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A data race was introduced in #9919 when the old synchronous storage API was replaced with an async storage API. The problem arises when `fetchWithCache` is called a second time while it's still processing another call. In this case, the `cachedFetch` object can become stale while blocked waiting for a fetch response, and result in a cache being overwritten unintentionally. See this example (options omitted for simplicity, and assuming an empty initial cache): ``` await Promise.all([ fetchWithCache('https://metamask.io/foo'), fetchWithCache('https://metamask.io/bar'), ] ``` The order of events could be as follows: 1. Empty cache retrieved for `/foo` route 2. Empty cache retrieved for `/bar` route 3. Call made to `/foo` route 4. Call made to `/bar` route 5. `/foo` response is added to the empty cache object retrieved in step 1, then is saved in the cache. 6. `/bar` response is added to the empty cache object retrieved in step 2, then is saved in the cache. In step 6, the cache object saved would not contain the `/foo` response set in step 5. As a result, `/foo` would never be cached. This problem was resolved by embedding the URL being cached directly in the cache key. This prevents simultaneous responses from overwriting each others caches. Technically a data race still exists when handing simultaneous responses to the same route, but the result would be that the last call to finish would overwrite the previous. This seems acceptable. |
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