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Conditional write is just added to S3 2 month ago: https://aws.amazon.com/about-aws/whats-new/2024/08/amazon-s3...

Unfortunately this functionality is much more limited in S3 as you can only use `If-None-Match: *` to prevent overwrites. https://docs.aws.amazon.com/AmazonS3/latest/userguide/condit...

GCS also allows for conditional overwrites using `If-Match: <etag>` which means you can do optimistic concurrency control. https://cloud.google.com/storage/docs/request-preconditions

Yeah, it might still be possible to implement a mutex based on just the existence of an object, but it'll be harder to add expiration/liveness which I find essential.

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