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9d9b9d46f3
Move responsibility of generating the cancel key to the backend process. The cancel key is now generated after forking, and the backend advertises it in the ProcSignal array. When a cancel request arrives, the backend handling it scans the ProcSignal array to find the target pid and cancel key. This is similar to how this previously worked in the EXEC_BACKEND case with the ShmemBackendArray, just reusing the ProcSignal array. One notable change is that we no longer generate cancellation keys for non-backend processes. We generated them before just to prevent a malicious user from canceling them; the keys for non-backend processes were never actually given to anyone. There is now an explicit flag indicating whether a process has a valid key or not. I wrote this originally in preparation for supporting longer cancel keys, but it's a nice cleanup on its own. Reviewed-by: Jelte Fennema-Nio Discussion: https://www.postgresql.org/message-id/508d0505-8b7a-4864-a681-e7e5edfe32aa@iki.fi