Amazon S3 Adds Put-If-Match (Compare-and-Swap)
AWS (via Hacker News):
Amazon S3 can now perform conditional writes that evaluate if an object is unmodified before updating it. This helps you coordinate simultaneous writes to the same object and prevents multiple concurrent writers from unintentionally overwriting the object without knowing the state of its content. You can use this capability by providing the ETag of an object using S3 PutObject or CompleteMultipartUpload API requests in both S3 general purpose and directory buckets.
This will probably enable some cool stuff.
