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--- 2909,2960 ----
  </programlisting>
      </para>
     </sect2>
+    <sect2>
+     <title>Shared Memory and LWLocks in C-Language Functions</title>
+ 
+     <para>
+      Add-ins may reserve LWLocks and an allocation of shared memory on server
+      startup.  The add-in's shared library must be preloaded, by specifying
+      it in 
+      <xref linkend="guc-shared-preload-libraries"><indexterm><primary>shared-preload-libraries</></>,
+      and the shared memory must be reserved by calling:
+ <programlisting>
+ void RequestAddinShmemSpace(int size)
+ </programlisting>
+      from your <literal>_PG_init</> function.
+     </para>
+     <para>
+       LWLocks are reserved by calling:
+ <programlisting>
+ void RequestAddinLWLocks(int n)
+ </programlisting>
+       from <literal>_PG_init</>. 
+     </para>	
+     <para>
+       To avoid possible race-conditions, each backend should use the LWLock
+       <literal>AddinShmemInitLock</> when connecting to and intializing 
+       its allocation of shared memory, as shown here:
+       
+ <programlisting>
+         static mystruct *ptr = NULL;
+ 
+         if (!ptr)
+         {
+                 bool    found;
+ 
+                 LWLockAcquire(AddinShmemInitLock, LW_EXCLUSIVE);
+                 ptr = ShmemInitStruct("my struct name", size, &amp;found);
+                 if (!ptr)
+                         elog(ERROR, "out of shared memory");
+                 if (!found)
+                 {
+                         initialize contents of shmem area;
+                         acquire any requested LWLocks using:
+                         ptr->mylockid = LWLockAssign();
+                 }
+                 LWLockRelease(AddinShmemInitLock);
+         }
+ </programlisting>
+     </para>
+    </sect2>
    </sect1>