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Thomas Munro 5ffb7c7750 De-pessimize ConditionVariableCancelSleep(). 
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 bc971f4025 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 bc971f4025 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
2023-08-15 10:23:47 +12:00
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README 

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/.