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>Behavior in Threaded Programs</TITLE
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><A
NAME="LIBPQ-THREADING"
>29.17. Behavior in Threaded Programs</A
></H1
><A
NAME="AEN29000"
></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
>.  This function allows the querying of
<SPAN
CLASS="APPLICATION"
>libpq</SPAN
>'s thread-safe status:</P
><P
></P
><DIV
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><DL
><DT
><CODE
CLASS="FUNCTION"
>PQisthreadsafe</CODE
><A
NAME="AEN29016"
></A
></DT
><DD
><P
>       Returns the thread safety status of the <SPAN
CLASS="APPLICATION"
>libpq</SPAN
>
       library.
</P><PRE
CLASS="SYNOPSIS"
>int PQisthreadsafe();</PRE
><P></P
><P
>       Returns 1 if the <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> is thread-safe and
       0 if it is not.</P
></DD
></DL
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><P
>One thread 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
> and
<CODE
CLASS="FUNCTION"
>PQoidStatus</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
>.</P
><P
>If you are using Kerberos inside your application (in addition to inside 
<SPAN
CLASS="APPLICATION"
>libpq</SPAN
>), you will need to do locking around 
Kerberos calls because Kerberos functions are not thread-safe.  See 
function <CODE
CLASS="FUNCTION"
>PQregisterThreadLock</CODE
> in the 
<SPAN
CLASS="APPLICATION"
>libpq</SPAN
> source code for a way to do cooperative 
locking between <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> and your application.</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
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