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Historically, cancel_before_shmem_exit() just silently did nothing if the specified callback wasn't the top-of-stack. The folly of ignoring this case was exposed by the bugs fixed in 303640199 and bab150045, so let's make it throw elog(ERROR) instead. There is a decent argument to be made that PG_ENSURE_ERROR_CLEANUP should use some separate infrastructure, so it wouldn't break if something inside the guarded code decides to register a new before_shmem_exit callback. However, a survey of the surviving uses of before_shmem_exit() and PG_ENSURE_ERROR_CLEANUP doesn't show any plausible conflicts of that sort today, so for now we'll forgo the extra complexity. (It will almost certainly become necessary if anyone ever wants to wrap PG_ENSURE_ERROR_CLEANUP around 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 myself Discussion: https://postgr.es/m/CALj2ACWk7j4F2v2fxxYfrroOF=AdFNPr1WsV+AGtHAFQOqm_pw@mail.gmail.com
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download/ See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.