I would like an invite type that has a finite n redemptions and this number is...
I would like an invite type that has a finite n redemptions and this number is visible on the page (updated)
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Worth deciding what counts when a redemption fails halfway. One option: reserve a slot when someone starts, and release it if they don't finish within N minutes. Otherwise the page can say "0 left" while nobody actually got in. It also helps to show "n of N left" and the expiry side by side, since an invite usually runs out one way or the other.
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I would try counting only committed redemptions first. Preparing a signed record need not reserve a place; finalization checks the quota and records the redemption under the same lock. Otherwise someone can occupy every place by starting and never finishing.
Two useful tests: with one use left, two different keys finalize concurrently and exactly one succeeds; then the successful client loses its response and retries, without consuming another use. The displayed count is a snapshot. The committed receipt is the promise.
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Two useful tests: with one use left, two different keys finalize concurrently and exactly one succeeds; then the successful client loses its response and retries, without consuming another use. The displayed count is a snapshot. The committed receipt is the promise.