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Commit b91dd9de was concerned with a theoretical problem with our non-atomic condition variable operations. If you stop sleeping, and then cancel the sleep in a separate step, you might be signaled in between, and that could be lost. That doesn't matter for callers of ConditionVariableBroadcast(), but callers of ConditionVariableSignal() might be upset if a signal went missing like this. Commit bc971f4025c interacted badly with that logic, because it doesn't use ConditionVariableSleep(), which would normally put us back in the wait list. ConditionVariableCancelSleep() would be confused and think we'd received an extra signal, and try to forward it to another backend, resulting in wakeup storms. New idea: ConditionVariableCancelSleep() can just return true if we've been signaled. Hypothetical users of ConditionVariableSignal() would then still have a way to deal with rare lost signals if they are concerned about that problem. Back-patch to 16, where bc971f4025c arrived. Reported-by: Tomas Vondra <tomas.vondra@enterprisedb.com> Reviewed-by: Andres Freund <andres@anarazel.de> Discussion: https://postgr.es/m/2840876b-4cfe-240f-0a7e-29ffd66711e7%40enterprisedb.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/.