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Commitc9ae5cb

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Install an error check into cancel_before_shmem_exit().
Historically, cancel_before_shmem_exit() just silently did nothingif the specified callback wasn't the top-of-stack. The folly ofignoring this case was exposed by the bugs fixed in3036401 andbab1500, so let's make it throw elog(ERROR) instead.There is a decent argument to be made that PG_ENSURE_ERROR_CLEANUPshould use some separate infrastructure, so it wouldn't break ifsomething inside the guarded code decides to register a newbefore_shmem_exit callback. However, a survey of the survivinguses of before_shmem_exit() and PG_ENSURE_ERROR_CLEANUP doesn'tshow any plausible conflicts of that sort today, so for now we'llforgo the extra complexity. (It will almost certainly becomenecessary if anyone ever wants to wrap PG_ENSURE_ERROR_CLEANUParound arbitrary user-defined actions, though.)No backpatch, since this is developer support not a production issue.Bharath Rupireddy, per advice from Andres Freund, Robert Haas, and myselfDiscussion:https://postgr.es/m/CALj2ACWk7j4F2v2fxxYfrroOF=AdFNPr1WsV+AGtHAFQOqm_pw@mail.gmail.com
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  • src/backend/storage/ipc

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‎src/backend/storage/ipc/ipc.c

Lines changed: 6 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -381,9 +381,9 @@ on_shmem_exit(pg_on_exit_callback function, Datum arg)
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*cancel_before_shmem_exit
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*
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*this function removes a previously-registered before_shmem_exit
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*callback.For simplicity,only the latest entrycan be
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*removed. (We could work harder but there is no need for
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*current uses.)
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*callback.Weonlylook atthe latest entryfor removal, as we
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* expect callers to add and remove temporary before_shmem_exit
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* callbacks in strict LIFO order.
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* ----------------------------------------------------------------
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*/
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void
@@ -394,6 +394,9 @@ cancel_before_shmem_exit(pg_on_exit_callback function, Datum arg)
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==function&&
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before_shmem_exit_list[before_shmem_exit_index-1].arg==arg)
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--before_shmem_exit_index;
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else
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elog(ERROR,"before_shmem_exit callback (%p,0x%llx) is not the latest entry",
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function, (long long)arg);
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}
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/* ----------------------------------------------------------------

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