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<title>28.15.Behavior in Threaded Programs</title>
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<a name="libpq-threading"></a>28.15.Behavior in Threaded Programs</h2></div></div></div>
<a name="id686887"></a><p><span class="application">libpq</span> is reentrant and thread-safe if the
<code class="filename">configure</code> command-line option
<code class="literal">--enable-thread-safety</code> 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
<code class="filename">src/Makefile.global</code> for <code class="literal">PTHREAD_CFLAGS</code>
and <code class="literal">PTHREAD_LIBS</code>.</p>
<p>One restriction is that no two threads attempt to manipulate the same
<code class="structname">PGconn</code> 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><code class="structname">PGresult</code> 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 <code class="filename">src/tools/thread</code> to see if your
platform has thread-unsafe functions. This program is run
by <code class="filename">configure</code>, but for binary distributions
your library might not match the library used to build the binaries.</p>
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