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In the previous coding, timeout would be noticed and reported only when
poll() or socket() returned zero (or the equivalent behavior on Windows).
Ordinarily that should work well enough, but it seems conceivable that we
could get into a state where poll() always returns a nonzero value --- for
example, if it is noticing a condition on one of the file descriptors that
we do not think is reason to exit the loop. If that happened, we'd be in a
busy-wait loop that would fail to terminate even when the timeout expires.
We can make this more robust at essentially no cost, by deciding to exit
of our own accord if we compute a zero or negative time-remaining-to-wait.
Previously the code noted this but just clamped the time-remaining to zero,
expecting that we'd detect timeout on the next loop iteration.
Back-patch to 9.2. While 9.1 had a version of WaitLatchOrSocket, it was
primitive compared to later versions, and did not guarantee reliable
detection of timeouts anyway. (Essentially, this is a refinement of
commit 3e7fdcffd6, which was back-patched only as far as 9.2.)
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: http://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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.