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0f527f73bd
pgwin32_recv() has treated a non-error return of zero bytes from WSARecv() as being a reason to block ever since the current implementation was introduced in commit a4c40f140d23cefb. However, so far as one can tell from Microsoft's documentation, that is just wrong: what it means is graceful connection closure (in stream protocols) or receipt of a zero-length message (in message protocols), and neither case should result in blocking here. The only reason the code worked at all was that control then fell into the retry loop, which did *not* treat zero bytes specially, so we'd get out after only wasting some cycles. But as of 9.5 we do not normally reach the retry loop and so the bug is exposed, as reported by Shay Rojansky and diagnosed by Andres Freund. Remove the unnecessary test on the byte count, and rearrange the code in the retry loop so that it looks identical to the initial sequence. Back-patch of commit 90e61df8130dc7051a108ada1219fb0680cb3eb6. The original plan was to apply this only to 9.5 and up, but after discussion and buildfarm testing, it seems better to back-patch. The noblock code path has been at risk of this problem since it was introduced (in 9.0); if it did happen in pre-9.5 branches, the symptom would be that a walsender would wait indefinitely rather than noticing a loss of connection. While we lack proof that the case has been seen in the field, it seems possible that it's happened without being reported.
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/.