<literal>__builtin_constant_p</literal>.
    </para>
   </simplesect>

   <simplesect id="source-conventions-macros-inline">
    <title>Function-Like Macros and Inline Functions</title>
    <para>
     Both macros with arguments and <literal>static inline</literal>
     functions may be used. The latter are preferable if there are
     multiple-evaluation hazards when written as a macro, as e.g., the
     case with
<programlisting>
#define Max(x, y)       ((x) > (y) ? (x) : (y))
</programlisting>
     or when the macro would be very long. In other cases it's only
     possible to use macros, or at least easier.  For example because
     expressions of various types need to be passed to the macro.
    </para>
    <para>
     When the definition of an inline function references symbols
     (i.e., variables, functions) that are only available as part of the
     backend, the function may not be visible when included from frontend
     code.
<programlisting>
#ifndef FRONTEND
static inline MemoryContext
MemoryContextSwitchTo(MemoryContext context)
{
    MemoryContext old = CurrentMemoryContext;

    CurrentMemoryContext = context;
    return old;
}
#endif   /* FRONTEND */
</programlisting>
     In this example <literal>CurrentMemoryContext</literal>, which is only
     available in the backend, is referenced and the function thus
     hidden with a <literal>#ifndef FRONTEND</literal>. This rule
     exists because some compilers emit references to symbols
     contained in inline functions even if the function is not used.
    </para>
   </simplesect>

   <simplesect id="source-conventions-signal-handlers">
    <title>Writing Signal Handlers</title>
    <para>
     To be suitable to run inside a signal handler code has to be
     written very carefully. The fundamental problem is that, unless
     blocked, a signal handler can interrupt code at any time. If code
     inside the signal handler uses the same state as code outside
     chaos may ensue. As an example consider what happens if a signal
     handler tries to acquire a lock that's already held in the
     interrupted code.
    </para>
    <para>
     Barring special arrangements code in signal handlers may only
     call async-signal safe functions (as defined in POSIX) and access
     variables of type <literal>volatile sig_atomic_t</literal>. A few
     functions in <command>postgres</command> are also deemed signal safe, importantly
     <function>SetLatch()</function>.
    </para>
    <para>
     In most cases signal handlers should do nothing more than note
     that a signal has arrived, and wake up code running outside of
     the handler using a latch. An example of such a handler is the
     following:
<programlisting>
static void
handle_sighup(SIGNAL_ARGS)
{
    got_SIGHUP = true;
    SetLatch(MyLatch);
}
</programlisting>
    </para>
   </simplesect>

   <simplesect id="source-conventions-function-pointers">
    <title>Calling Function Pointers</title>

    <para>
     For clarity, it is preferred to explicitly dereference a function pointer
     when calling the pointed-to function if the pointer is a simple variable,
     for example:
<programlisting>
(*emit_log_hook) (edata);
</programlisting>
     (even though <literal>emit_log_hook(edata)</literal> would also work).
     When the function pointer is part of a structure, then the extra
     punctuation can and usually should be omitted, for example:
<programlisting>
paramInfo->paramFetch(paramInfo, paramId);
</programlisting>
    </para>
   </simplesect>
  </sect1>
 </chapter>