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>Behavior in Threaded Programs</TITLE
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><A
NAME="LIBPQ-THREADING"
>31.19. Behavior in Threaded Programs</A
></H1
><P
> <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> is reentrant and thread-safe by default.
You might need to use special 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
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><DL
><DT
><A
NAME="LIBPQ-PQISTHREADSAFE"
></A
><CODE
CLASS="FUNCTION"
>PQisthreadsafe</CODE
>
</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
></DIV
><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 normally read-only after creation,
and so can be passed around freely between threads. However, if you use
any of the <TT
CLASS="STRUCTNAME"
>PGresult</TT
>-modifying functions described in
<A
HREF="libpq-misc.html"
>Section 31.11</A
> or <A
HREF="libpq-events.html"
>Section 31.13</A
>, it's up
to you to avoid concurrent operations on the same <TT
CLASS="STRUCTNAME"
>PGresult</TT
>,
too.
</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.
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