Go’s golang.org/x/sync/singleflight package deduplicates concurrent requests for the same resource, executing the function once and sharing the result.
Key Takeaways
singleflight.Group.Do(key, fn) ensures only one in-flight call per key; all waiting goroutines receive the same result and error.
Useful when caching is not viable or results change frequently – complements but does not replace a cache layer.
Combining singleflight with sync.Map covers both deduplication (in-flight) and caching (post-fetch), as shown in the weather service example.
Key design: string key management determines deduplication scope; poor key choice causes missed deduplication or incorrect result sharing.
Error propagation is shared too – a single upstream failure returns that error to all waiting callers simultaneously.
