I686LINUX/util/I686LINUX/doc/postgresql/html/libpq-threading.html

   1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
   2 <HTML
   3 ><HEAD
   4 ><TITLE
   5 >Behavior in Threaded Programs</TITLE
   6 ><META
   7 NAME="GENERATOR"
   8 CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
   9 REV="MADE"
  10 HREF="mailto:pgsql-docs@postgresql.org"><LINK
  11 REL="HOME"
  12 TITLE="PostgreSQL 7.4.1 Documentation"
  13 HREF="index.html"><LINK
  14 REL="UP"
  15 TITLE="libpq - C Library"
  16 HREF="libpq.html"><LINK
  17 REL="PREVIOUS"
  18 TITLE="The Password File"
  19 HREF="libpq-pgpass.html"><LINK
  20 REL="NEXT"
  21 TITLE="Building libpq Programs"
  22 HREF="libpq-build.html"><LINK
  23 REL="STYLESHEET"
  24 TYPE="text/css"
  25 HREF="stylesheet.css"><META
  26 NAME="creation"
  27 CONTENT="2003-12-22T03:48:47"></HEAD
  28 ><BODY
  29 CLASS="SECT1"
  30 ><DIV
  31 CLASS="NAVHEADER"
  32 ><TABLE
  33 SUMMARY="Header navigation table"
  34 WIDTH="100%"
  35 BORDER="0"
  36 CELLPADDING="0"
  37 CELLSPACING="0"
  38 ><TR
  39 ><TH
  40 COLSPAN="5"
  41 ALIGN="center"
  42 VALIGN="bottom"
  43 >PostgreSQL 7.4.1 Documentation</TH
  44 ></TR
  45 ><TR
  46 ><TD
  47 WIDTH="10%"
  48 ALIGN="left"
  49 VALIGN="top"
  50 ><A
  51 HREF="libpq-pgpass.html"
  52 ACCESSKEY="P"
  53 >Prev</A
  54 ></TD
  55 ><TD
  56 WIDTH="10%"
  57 ALIGN="left"
  58 VALIGN="top"
  59 ><A
  60 HREF="libpq.html"
  61 >Fast Backward</A
  62 ></TD
  63 ><TD
  64 WIDTH="60%"
  65 ALIGN="center"
  66 VALIGN="bottom"
  67 >Chapter 27. <SPAN
  68 CLASS="APPLICATION"
  69 >libpq</SPAN
  70 > - C Library</TD
  71 ><TD
  72 WIDTH="10%"
  73 ALIGN="right"
  74 VALIGN="top"
  75 ><A
  76 HREF="libpq.html"
  77 >Fast Forward</A
  78 ></TD
  79 ><TD
  80 WIDTH="10%"
  81 ALIGN="right"
  82 VALIGN="top"
  83 ><A
  84 HREF="libpq-build.html"
  85 ACCESSKEY="N"
  86 >Next</A
  87 ></TD
  88 ></TR
  89 ></TABLE
  90 ><HR
  91 ALIGN="LEFT"
  92 WIDTH="100%"></DIV
  93 ><DIV
  94 CLASS="SECT1"
  95 ><H1
  96 CLASS="SECT1"
  97 ><A
  98 NAME="LIBPQ-THREADING"
  99 >27.12. Behavior in Threaded Programs</A
 100 ></H1
 101 ><A
 102 NAME="AEN21902"
 103 ></A
 104 ><P
 105 ><SPAN
 106 CLASS="APPLICATION"
 107 >libpq</SPAN
 108 > is reentrant and thread-safe if the
 109 <TT
 110 CLASS="FILENAME"
 111 >configure</TT
 112 > command-line option
 113 <TT
 114 CLASS="LITERAL"
 115 >--enable-thread-safety</TT
 116 > has been used when the PostgreSQL
 117 distribution was built.
 118 In addition, you might need to use additional compiler command-line
 119 options when you compile your application code.  Refer to your system's
 120 documentation for information about how to build thread-enabled
 121 applications.</P
 122 ><P
 123 >One restriction is that no two threads attempt to manipulate the same
 124 <TT
 125 CLASS="STRUCTNAME"
 126 >PGconn</TT
 127 > object at the same time. In particular, you cannot
 128 issue concurrent commands from different threads through the same
 129 connection object. (If you need to run concurrent commands, start up
 130 multiple connections.)</P
 131 ><P
 132 ><TT
 133 CLASS="STRUCTNAME"
 134 >PGresult</TT
 135 > objects are read-only after creation, and so can be
 136 passed around freely between threads.</P
 137 ><P
 138 >The deprecated functions <CODE
 139 CLASS="FUNCTION"
 140 >PQoidStatus</CODE
 141 > and
 142 <CODE
 143 CLASS="FUNCTION"
 144 >fe_setauthsvc</CODE
 145 > are not thread-safe and should not be
 146 used in multithread programs.  <CODE
 147 CLASS="FUNCTION"
 148 >PQoidStatus</CODE
 149 > can be
 150 replaced by <CODE
 151 CLASS="FUNCTION"
 152 >PQoidValue</CODE
 153 >.  There is no good reason to
 154 call <CODE
 155 CLASS="FUNCTION"
 156 >fe_setauthsvc</CODE
 157 > at all.</P
 158 ><P
 159 ><SPAN
 160 CLASS="APPLICATION"
 161 >libpq</SPAN
 162 > applications that use the
 163 <TT
 164 CLASS="LITERAL"
 165 >crypt</TT
 166 > authentication method rely on the
 167 <TT
 168 CLASS="LITERAL"
 169 >crypt()</TT
 170 > operating system function, which is often
 171 not thread-safe.<A
 172 NAME="AEN21923"
 173 ></A
 174 > It is better to use the <TT
 175 CLASS="LITERAL"
 176 >md5</TT
 177 > method,
 178 which is thread-safe on all platforms.</P
 179 ></DIV
 180 ><DIV
 181 CLASS="NAVFOOTER"
 182 ><HR
 183 ALIGN="LEFT"
 184 WIDTH="100%"><TABLE
 185 SUMMARY="Footer navigation table"
 186 WIDTH="100%"
 187 BORDER="0"
 188 CELLPADDING="0"
 189 CELLSPACING="0"
 190 ><TR
 191 ><TD
 192 WIDTH="33%"
 193 ALIGN="left"
 194 VALIGN="top"
 195 ><A
 196 HREF="libpq-pgpass.html"
 197 ACCESSKEY="P"
 198 >Prev</A
 199 ></TD
 200 ><TD
 201 WIDTH="34%"
 202 ALIGN="center"
 203 VALIGN="top"
 204 ><A
 205 HREF="index.html"
 206 ACCESSKEY="H"
 207 >Home</A
 208 ></TD
 209 ><TD
 210 WIDTH="33%"
 211 ALIGN="right"
 212 VALIGN="top"
 213 ><A
 214 HREF="libpq-build.html"
 215 ACCESSKEY="N"
 216 >Next</A
 217 ></TD
 218 ></TR
 219 ><TR
 220 ><TD
 221 WIDTH="33%"
 222 ALIGN="left"
 223 VALIGN="top"
 224 >The Password File</TD
 225 ><TD
 226 WIDTH="34%"
 227 ALIGN="center"
 228 VALIGN="top"
 229 ><A
 230 HREF="libpq.html"
 231 ACCESSKEY="U"
 232 >Up</A
 233 ></TD
 234 ><TD
 235 WIDTH="33%"
 236 ALIGN="right"
 237 VALIGN="top"
 238 >Building <SPAN
 239 CLASS="APPLICATION"
 240 >libpq</SPAN
 241 > Programs</TD
 242 ></TR
 243 ></TABLE
 244 ></DIV
 245 ></BODY
 246 ></HTML
 247 >