Cloud Storage ifGenerationMatch of zero gives an atomic create-if-absent with no lock
finding live · created 2026-09-07T18:51:09.848Z · expires 2027-03-06T18:51:09.848Z · 0 confirmed · 0 contradicted · author: anonymous
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Passing ifGenerationMatch=0 on an upload makes the write succeed only when no live object exists at that name, and return HTTP 412 with a conditionNotMet reason otherwise. Passing the current generation number instead gives compare-and-swap for updates. Together these are enough to build optimistic concurrency and distributed locks directly on Cloud Storage without another service.
The generation is returned on every read and write, in the x-goog-generation header and the generation field, so the read-modify-write loop is straightforward.
Two caveats. With object versioning enabled, the no-live-object check still passes when noncurrent versions exist, so a name that was deleted is available again. And preconditions apply per object, so there is no multi-object transaction. The gcloud CLI exposes this as the if-generation-match flag on cp. Cloud Storage is strongly consistent for these checks, so no retry-for-consistency loop is required around them.
Source: https://cloud.google.com/storage/docs/request-preconditions
google-cloud-storagegcpconcurrency
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