<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Behavior in Threaded Programs</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 8.0.11 Documentation" HREF="index.html"><LINK REL="UP" TITLE="libpq - C Library" HREF="libpq.html"><LINK REL="PREVIOUS" TITLE="SSL Support" HREF="libpq-ssl.html"><LINK REL="NEXT" TITLE="Building libpq Programs" HREF="libpq-build.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2007-02-02T03:57:22"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" >PostgreSQL 8.0.11 Documentation</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="libpq-ssl.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="libpq.html" >Fast Backward</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 27. <SPAN CLASS="APPLICATION" >libpq</SPAN > - C Library</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="libpq.html" >Fast Forward</A ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="libpq-build.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="LIBPQ-THREADING" >27.14. Behavior in Threaded Programs</A ></H1 ><A NAME="AEN24831" ></A ><P ><SPAN CLASS="APPLICATION" >libpq</SPAN > is reentrant and thread-safe if the <TT CLASS="FILENAME" >configure</TT > command-line option <TT CLASS="LITERAL" >--enable-thread-safety</TT > was used when the <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > distribution was built. In addition, you might need to use additional compiler command-line options when you compile your application code. Refer to your system's documentation for information about how to build thread-enabled applications, or look in <TT CLASS="FILENAME" >src/Makefile.global</TT > for <TT CLASS="LITERAL" >PTHREAD_CFLAGS</TT > and <TT CLASS="LITERAL" >PTHREAD_LIBS</TT >.</P ><P >One restriction is that no two threads attempt to manipulate the same <TT CLASS="STRUCTNAME" >PGconn</TT > object at the same time. In particular, you cannot issue concurrent commands from different threads through the same connection object. (If you need to run concurrent commands, use multiple connections.)</P ><P ><TT CLASS="STRUCTNAME" >PGresult</TT > objects are read-only after creation, and so can be passed around freely between threads.</P ><P >The deprecated functions <CODE CLASS="FUNCTION" >PQrequestCancel</CODE >, <CODE CLASS="FUNCTION" >PQoidStatus</CODE > and <CODE CLASS="FUNCTION" >fe_setauthsvc</CODE > are not thread-safe and should not be used in multithread programs. <CODE CLASS="FUNCTION" >PQrequestCancel</CODE > can be replaced by <CODE CLASS="FUNCTION" >PQcancel</CODE >. <CODE CLASS="FUNCTION" >PQoidStatus</CODE > can be replaced by <CODE CLASS="FUNCTION" >PQoidValue</CODE >. There is no good reason to call <CODE CLASS="FUNCTION" >fe_setauthsvc</CODE > at all.</P ><P ><SPAN CLASS="APPLICATION" >libpq</SPAN > applications that use the <TT CLASS="LITERAL" >crypt</TT > authentication method rely on the <TT CLASS="LITERAL" >crypt()</TT > operating system function, which is often not thread-safe.<A NAME="AEN24859" ></A > It is better to use the <TT CLASS="LITERAL" >md5</TT > method, which is thread-safe on all platforms.</P ><P >If you experience problems with threaded applications, run the program in <TT CLASS="FILENAME" >src/tools/thread</TT > to see if your platform has thread-unsafe functions. This program is run by <TT CLASS="FILENAME" >configure</TT >, but for binary distributions your library might not match the library used to build the binaries.</P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="libpq-ssl.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="libpq-build.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >SSL Support</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="libpq.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Building <SPAN CLASS="APPLICATION" >libpq</SPAN > Programs</TD ></TR ></TABLE ></DIV ></BODY ></HTML >
