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fix: take a consumer handler slot before receiving - #1166
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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Oct 27, 2026
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Take the handler slot before receiving, so the consumer only holds a message it can run now.
The consumer received the next message and then waited for a free handler slot. With every handler busy, that message waited for a handler to finish while its visibility timeout ran. If the consumer shut down during the wait, the message was dropped without an ack or nack and came back only after the timeout.
It is one message per consumer: the broker SDKs prefetch, so the rest of the backlog waits in the SDK either way. GCP Pub/Sub manages its own concurrency and doesn't use this path.
TestConsumer_ReceivesOnlyWithFreeSlotfails on the old code: with both slots busy, the consumer received a third message.🤖 Generated with Claude Code