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<FONT color=3D#ffa500>sub</FONT> <FONT color=3D#b2dfee>REAPER</FONT> =
<FONT color=3D#00ffff>{</FONT>
    <FONT color=3D#cdcd00>1</FONT> <FONT color=3D#ffa500>until</FONT> =
<FONT color=3D#00ffff>(</FONT><FONT color=3D#cdcd00>-1</FONT> =3D=3D =
<FONT color=3D#98fb98>waitpid</FONT><FONT color=3D#00ffff>(</FONT><FONT =
color=3D#cdcd00>-1</FONT>, WNOHANG<FONT color=3D#00ffff>));</FONT>
    <FONT color=3D#cdcd00>$SIG</FONT><FONT color=3D#00ffff>{</FONT><FONT =
color=3D#00cd00>CHLD</FONT><FONT color=3D#00ffff>}</FONT> =3D =
\&amp;REAPER<FONT color=3D#00ffff>;</FONT>                 <FONT =
color=3D#bebebe># unless $] &gt;=3D 5.002
</FONT><FONT color=3D#00ffff>}</FONT>

<FONT color=3D#cdcd00>$SIG</FONT><FONT color=3D#00ffff>{</FONT><FONT =
color=3D#00cd00>CHLD</FONT><FONT color=3D#00ffff>}</FONT> =3D =
\&amp;REAPER<FONT color=3D#00ffff>;</FONT>

<FONT color=3D#ffa500>while</FONT> <FONT =
color=3D#00ffff>(</FONT>$hisaddr =3D <FONT =
color=3D#98fb98>accept</FONT><FONT color=3D#00ffff>(</FONT>CLIENT, =
SERVER<FONT color=3D#00ffff>))</FONT> <FONT color=3D#00ffff>{</FONT>
    <FONT color=3D#ffa500>next</FONT> <FONT color=3D#ffa500>if</FONT> =
$pid =3D <FONT color=3D#98fb98>fork</FONT><FONT color=3D#00ffff>;</FONT> =
                   <FONT color=3D#bebebe># parent
</FONT>    <FONT color=3D#ffa500>die</FONT> <FONT color=3D#00cd00>"fork: =
$!"</FONT> <FONT color=3D#ffa500>unless</FONT> <FONT =
color=3D#ff7f50>defined</FONT> $pid<FONT color=3D#00ffff>;</FONT>     =
<FONT color=3D#bebebe># failure
</FONT>    <FONT color=3D#bebebe># otherwise child
</FONT>    <FONT color=3D#98fb98>close</FONT><FONT =
color=3D#00ffff>(</FONT>SERVER<FONT color=3D#00ffff>);</FONT>            =
              <FONT color=3D#bebebe># no use to child
</FONT>    <FONT color=3D#bebebe># ... do something
</FONT>    <FONT color=3D#ffa500>exit</FONT><FONT =
color=3D#00ffff>;</FONT>                                   <FONT =
color=3D#bebebe># child leaves
</FONT><FONT color=3D#00ffff>}</FONT> <FONT =
color=3D#ffa500>continue</FONT> <FONT color=3D#00ffff>{</FONT><FONT =
color=3D#43cd80> </FONT>
    <FONT color=3D#98fb98>close</FONT><FONT =
color=3D#00ffff>(</FONT>CLIENT<FONT color=3D#00ffff>);</FONT>            =
              <FONT color=3D#bebebe># no use to parent
</FONT><FONT color=3D#00ffff>}</FONT>
<FONT color=3D#bebebe>#-----------------------------
</FONT></PRE></FONT></TD></TR></TBODY></TABLE></DIV>
<DIV class=3DSECT2>
<H2 class=3DSECT2><A name=3DAEN955>Pre-Forking Servers</A></H2>
<TABLE width=3D"100%" bgColor=3D#2f4f4f border=3D0>
  <TBODY>
  <TR>
    <TD><PRE class=3DSCREEN><FONT color=3D#f5deb3 size=3D+1><FONT =
color=3D#bebebe>#-----------------------------
# <FONT size=3D-1><A =
href=3D"http://pleac.sourceforge.net/include/perl/ch17/preforker">downloa=
d the following standalone program</A></FONT>
#!/usr/bin/perl
# preforker - server who forks first
</FONT><FONT color=3D#ffa500>use</FONT> <FONT =
color=3D#b2dfee>IO::Socket</FONT><FONT color=3D#00ffff>;</FONT>
<FONT color=3D#ffa500>use</FONT> <FONT =
color=3D#b2dfee>Symbol</FONT><FONT color=3D#00ffff>;</FONT>
<FONT color=3D#ffa500>use</FONT> <FONT color=3D#b2dfee>POSIX</FONT><FONT =
color=3D#00ffff>;</FONT>

<FONT color=3D#bebebe># establish SERVER socket, bind and listen.
</FONT>$server =3D IO::Socket::INET-&gt;new<FONT =
color=3D#00ffff>(</FONT><FONT color=3D#00cd00>LocalPort</FONT> =3D&gt; =
<FONT color=3D#cdcd00>6969</FONT>,
                                <FONT color=3D#00cd00>Type</FONT>      =
=3D&gt; SOCK_STREAM,
                                <FONT color=3D#00cd00>Proto</FONT>     =
=3D&gt; <FONT color=3D#00cd00>'tcp'</FONT>,
                                <FONT color=3D#00cd00>Reuse</FONT>     =
=3D&gt; <FONT color=3D#cdcd00>1</FONT>,
                                <FONT color=3D#00cd00>Listen</FONT>    =
=3D&gt; <FONT color=3D#cdcd00>10</FONT> <FONT color=3D#00ffff>)</FONT>
  <FONT color=3D#98fb98>or</FONT> <FONT color=3D#ffa500>die</FONT> <FONT =
color=3D#00cd00>"making socket: $@\n"</FONT><FONT =
color=3D#00ffff>;</FONT>

<FONT color=3D#bebebe># global variables
</FONT>$PREFORK                =3D <FONT color=3D#cdcd00>5</FONT><FONT =
color=3D#00ffff>;</FONT>        <FONT color=3D#bebebe># number of =
children to maintain
</FONT>$MAX_CLIENTS_PER_CHILD  =3D <FONT color=3D#cdcd00>5</FONT><FONT =
color=3D#00ffff>;</FONT>        <FONT color=3D#bebebe># number of =
clients each child should process
</FONT><FONT color=3D#cdcd00>%children</FONT>               =3D <FONT =
color=3D#00ffff>();</FONT>       <FONT color=3D#bebebe># keys are =
current child process IDs
</FONT>$children               =3D <FONT color=3D#cdcd00>0</FONT><FONT =
color=3D#00ffff>;</FONT>        <FONT color=3D#bebebe># current number =
of children
</FONT>
<FONT color=3D#ffa500>sub</FONT> <FONT color=3D#b2dfee>REAPER</FONT> =
<FONT color=3D#00ffff>{</FONT>                        <FONT =
color=3D#bebebe># takes care of dead children
</FONT>    <FONT color=3D#cdcd00>$SIG</FONT><FONT =
color=3D#00ffff>{</FONT><FONT color=3D#00cd00>CHLD</FONT><FONT =
color=3D#00ffff>}</FONT> =3D \&amp;REAPER<FONT color=3D#00ffff>;</FONT>
    <FONT color=3D#ffa500>my</FONT> <FONT color=3D#9ac0cd>$pid</FONT> =
=3D <FONT color=3D#98fb98>wait</FONT><FONT color=3D#00ffff>;</FONT>
    $children --<FONT color=3D#00ffff>;</FONT>
    <FONT color=3D#ff7f50>delete</FONT> <FONT =
color=3D#cdcd00>$children</FONT><FONT color=3D#00ffff>{</FONT>$pid<FONT =
color=3D#00ffff>};</FONT>
<FONT color=3D#00ffff>}</FONT>

<FONT color=3D#ffa500>sub</FONT> <FONT color=3D#b2dfee>HUNTSMAN</FONT> =
<FONT color=3D#00ffff>{</FONT>                      <FONT =
color=3D#bebebe># signal handler for SIGINT
</FONT>    <FONT color=3D#ffa500>local</FONT><FONT =
color=3D#00ffff>(</FONT><FONT color=3D#cdcd00>$SIG</FONT><FONT =
color=3D#00ffff>{</FONT><FONT color=3D#00cd00>CHLD</FONT><FONT =
color=3D#00ffff>})</FONT> =3D <FONT color=3D#00cd00>'IGNORE'</FONT><FONT =
color=3D#00ffff>;</FONT>   <FONT color=3D#bebebe># we're going to kill =
our children
</FONT>    <FONT color=3D#98fb98>kill</FONT> <FONT =
color=3D#00cd00>'INT'</FONT> =3D&gt; <FONT color=3D#ff7f50>keys</FONT> =
<FONT color=3D#cdcd00>%children</FONT><FONT color=3D#00ffff>;</FONT>
    <FONT color=3D#ffa500>exit</FONT><FONT color=3D#00ffff>;</FONT>      =
                     <FONT color=3D#bebebe># clean up with dignity
</FONT><FONT color=3D#00ffff>}</FONT>

<FONT color=3D#43cd80>    </FONT>
<FONT color=3D#bebebe># Fork off our children.
</FONT><FONT color=3D#ffa500>for</FONT> <FONT =
color=3D#00ffff>(</FONT><FONT color=3D#cdcd00>1</FONT> .. $PREFORK<FONT =
color=3D#00ffff>)</FONT> <FONT color=3D#00ffff>{</FONT>
    make_new_child<FONT color=3D#00ffff>();</FONT>
<FONT color=3D#00ffff>}</FONT>

<FONT color=3D#bebebe># Install signal handlers.
</FONT><FONT color=3D#cdcd00>$SIG</FONT><FONT =
color=3D#00ffff>{</FONT><FONT color=3D#00cd00>CHLD</FONT><FONT =
color=3D#00ffff>}</FONT> =3D \&amp;REAPER<FONT color=3D#00ffff>;</FONT>
<FONT color=3D#cdcd00>$SIG</FONT><FONT color=3D#00ffff>{</FONT><FONT =
color=3D#00cd00>INT</FONT><FONT color=3D#00ffff>}</FONT>  =3D =
\&amp;HUNTSMAN<FONT color=3D#00ffff>;</FONT>

<FONT color=3D#bebebe># And maintain the population.
</FONT><FONT color=3D#ffa500>while</FONT> <FONT =
color=3D#00ffff>(</FONT><FONT color=3D#cdcd00>1</FONT><FONT =
color=3D#00ffff>)</FONT> <FONT color=3D#00ffff>{</FONT>
    <FONT color=3D#98fb98>sleep</FONT><FONT color=3D#00ffff>;</FONT>     =
                     <FONT color=3D#bebebe># wait for a signal (i.e., =
child's death)
</FONT>    <FONT color=3D#ffa500>for</FONT> <FONT =
color=3D#00ffff>(</FONT>$i =3D $children<FONT color=3D#00ffff>;</FONT> =
$i &lt; $PREFORK<FONT color=3D#00ffff>;</FONT> $i++<FONT =
color=3D#00ffff>)</FONT> <FONT color=3D#00ffff>{</FONT>
        make_new_child<FONT color=3D#00ffff>();</FONT>           <FONT =
color=3D#bebebe># top up the child pool
</FONT>    <FONT color=3D#00ffff>}</FONT>
<FONT color=3D#00ffff>}</FONT>

<FONT color=3D#ffa500>sub</FONT> <FONT =
color=3D#b2dfee>make_new_child</FONT> <FONT color=3D#00ffff>{</FONT>
    <FONT color=3D#ffa500>my</FONT> <FONT =
color=3D#9ac0cd>$pid</FONT><FONT color=3D#00ffff>;</FONT>
    <FONT color=3D#ffa500>my</FONT> <FONT =
color=3D#9ac0cd>$sigset</FONT><FONT color=3D#00ffff>;</FONT>
<FONT color=3D#43cd80>    </FONT>
    <FONT color=3D#bebebe># block signal for fork
</FONT>    $sigset =3D POSIX::SigSet-&gt;new<FONT =
color=3D#00ffff>(</FONT>SIGINT<FONT color=3D#00ffff>);</FONT>
    sigprocmask<FONT color=3D#00ffff>(</FONT>SIG_BLOCK, $sigset<FONT =
color=3D#00ffff>)</FONT>
        <FONT color=3D#98fb98>or</FONT> <FONT color=3D#ffa500>die</FONT> =
<FONT color=3D#00cd00>"Can't block SIGINT for fork: $!\n"</FONT><FONT =
color=3D#00ffff>;</FONT>
<FONT color=3D#43cd80>    </FONT>
    <FONT color=3D#ffa500>die</FONT> <FONT color=3D#00cd00>"fork: =
$!"</FONT> <FONT color=3D#ffa500>unless</FONT> <FONT =
color=3D#ff7f50>defined</FONT> <FONT color=3D#00ffff>(</FONT>$pid =3D =
<FONT color=3D#98fb98>fork</FONT><FONT color=3D#00ffff>);</FONT>
<FONT color=3D#43cd80>    </FONT>
    <FONT color=3D#ffa500>if</FONT> <FONT =
color=3D#00ffff>(</FONT>$pid<FONT color=3D#00ffff>)</FONT> <FONT =
color=3D#00ffff>{</FONT>
        <FONT color=3D#bebebe># Parent records the child's birth and =
returns.
</FONT>        sigprocmask<FONT color=3D#00ffff>(</FONT>SIG_UNBLOCK, =
$sigset<FONT color=3D#00ffff>)</FONT>
            <FONT color=3D#98fb98>or</FONT> <FONT =
color=3D#ffa500>die</FONT> <FONT color=3D#00cd00>"Can't unblock SIGINT =
for fork: $!\n"</FONT><FONT color=3D#00ffff>;</FONT>
        <FONT color=3D#cdcd00>$children</FONT><FONT =
color=3D#00ffff>{</FONT>$pid<FONT color=3D#00ffff>}</FONT> =3D <FONT =
color=3D#cdcd00>1</FONT><FONT color=3D#00ffff>;</FONT>
        $children++<FONT color=3D#00ffff>;</FONT>
        <FONT color=3D#ffa500>return</FONT><FONT =
color=3D#00ffff>;</FONT>
    <FONT color=3D#00ffff>}</FONT> <FONT color=3D#ffa500>else</FONT> =
<FONT color=3D#00ffff>{</FONT>
        <FONT color=3D#bebebe># Child can *not* return from this =
subroutine.
</FONT>        <FONT color=3D#cdcd00>$SIG</FONT><FONT =
color=3D#00ffff>{</FONT><FONT color=3D#00cd00>INT</FONT><FONT =
color=3D#00ffff>}</FONT> =3D <FONT color=3D#00cd00>'DEFAULT'</FONT><FONT =
color=3D#00ffff>;</FONT>      <FONT color=3D#bebebe># make SIGINT kill =
us as it did before
</FONT><FONT color=3D#43cd80>    </FONT>
        <FONT color=3D#bebebe># unblock signals
</FONT>        sigprocmask<FONT color=3D#00ffff>(</FONT>SIG_UNBLOCK, =
$sigset<FONT color=3D#00ffff>)</FONT>
            <FONT color=3D#98fb98>or</FONT> <FONT =
color=3D#ffa500>die</FONT> <FONT color=3D#00cd00>"Can't unblock SIGINT =
for fork: $!\n"</FONT><FONT color=3D#00ffff>;</FONT>
<FONT color=3D#43cd80>    </FONT>
        <FONT color=3D#bebebe># handle connections until we've reached =
$MAX_CLIENTS_PER_CHILD
</FONT>        <FONT color=3D#ffa500>for</FONT> <FONT =
color=3D#00ffff>(</FONT>$i=3D<FONT color=3D#cdcd00>0</FONT><FONT =
color=3D#00ffff>;</FONT> $i &lt; $MAX_CLIENTS_PER_CHILD<FONT =
color=3D#00ffff>;</FONT> $i++<FONT color=3D#00ffff>)</FONT> <FONT =
color=3D#00ffff>{</FONT>
            $client =3D $server-&gt;<FONT =
color=3D#98fb98>accept</FONT><FONT color=3D#00ffff>()</FONT>     <FONT =
color=3D#98fb98>or</FONT> <FONT color=3D#ffa500>last</FONT><FONT =
color=3D#00ffff>;</FONT>
            <FONT color=3D#bebebe># do something with the connection
</FONT>        <FONT color=3D#00ffff>}</FONT>
<FONT color=3D#43cd80>    </FONT>
        <FONT color=3D#bebebe># tidy up gracefully and finish
</FONT><FONT color=3D#43cd80>    </FONT>
        <FONT color=3D#bebebe># this exit is VERY important, otherwise =
the child will become
</FONT>        <FONT color=3D#bebebe># a producer of more and more =
children, forking yourself into
</FONT>        <FONT color=3D#bebebe># process death.
</FONT>        <FONT color=3D#ffa500>exit</FONT><FONT =
color=3D#00ffff>;</FONT>
    <FONT color=3D#00ffff>}</FONT>
<FONT color=3D#00ffff>}</FONT>

<FONT color=3D#bebebe>#-----------------------------
</FONT></PRE></FONT></TD></TR></TBODY></TABLE></DIV>
<DIV class=3DSECT2>
<H2 class=3DSECT2><A name=3DAEN958>Non-Forking Servers</A></H2>
<TABLE width=3D"100%" bgColor=3D#2f4f4f border=3D0>
  <TBODY>
  <TR>
    <TD><PRE class=3DSCREEN><FONT color=3D#f5deb3 size=3D+1><FONT =
color=3D#bebebe>#-----------------------------
# <FONT size=3D-1><A =
href=3D"http://pleac.sourceforge.net/include/perl/ch17/nonforker">downloa=
d the following standalone program</A></FONT>
#!/usr/bin/perl -w
# nonforker - server who multiplexes without forking
</FONT><FONT color=3D#ffa500>use</FONT> <FONT =
color=3D#b2dfee>POSIX</FONT><FONT color=3D#00ffff>;</FONT>
<FONT color=3D#ffa500>use</FONT> <FONT =
color=3D#b2dfee>IO::Socket</FONT><FONT color=3D#00ffff
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