214 lines
16 KiB
HTML
214 lines
16 KiB
HTML
<?xml version="1.0" encoding="UTF-8"?>
|
|
<!DOCTYPE html
|
|
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
|
<html lang="en-us" xml:lang="en-us">
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
|
<meta name="security" content="public" />
|
|
<meta name="Robots" content="index,follow" />
|
|
<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
|
|
<meta name="DC.Type" content="reference" />
|
|
<meta name="DC.Title" content="Socket application design recommendations" />
|
|
<meta name="abstract" content="Before working with socket applications, assess the functional requirements, goals, and needs of the socket application." />
|
|
<meta name="description" content="Before working with socket applications, assess the functional requirements, goals, and needs of the socket application." />
|
|
<meta name="DC.Relation" scheme="URI" content="rzab6soxoverview.htm" />
|
|
<meta name="DC.Relation" scheme="URI" content="../apis/dossrmfh.htm" />
|
|
<meta name="DC.Relation" scheme="URI" content="xasynchi0.htm" />
|
|
<meta name="DC.Relation" scheme="URI" content="asynchi0.htm" />
|
|
<meta name="DC.Relation" scheme="URI" content="xnonblock.htm" />
|
|
<meta name="DC.Relation" scheme="URI" content="xdescriptors.htm" />
|
|
<meta name="DC.Relation" scheme="URI" content="xnonblock.htm" />
|
|
<meta name="copyright" content="(C) Copyright IBM Corporation 2001, 2006" />
|
|
<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 2001, 2006" />
|
|
<meta name="DC.Format" content="XHTML" />
|
|
<meta name="DC.Identifier" content="designrec" />
|
|
<meta name="DC.Language" content="en-us" />
|
|
<!-- All rights reserved. Licensed Materials Property of IBM -->
|
|
<!-- US Government Users Restricted Rights -->
|
|
<!-- Use, duplication or disclosure restricted by -->
|
|
<!-- GSA ADP Schedule Contract with IBM Corp. -->
|
|
<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
|
|
<link rel="stylesheet" type="text/css" href="./ic.css" />
|
|
<title>Socket application design recommendations</title>
|
|
</head>
|
|
<body id="designrec"><a name="designrec"><!-- --></a>
|
|
<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
|
|
<h1 class="topictitle1">Socket application design recommendations</h1>
|
|
<div><p>Before working with socket applications, assess the functional
|
|
requirements, goals, and needs of the socket application.</p>
|
|
<div class="section"><p>Consider performance requirements and system resource impacts
|
|
of the application too. The following list of recommendations helps you address
|
|
some of these issues for your socket application and points out
|
|
better ways to use sockets and to design your socket applications:</p>
|
|
</div>
|
|
<div class="section">
|
|
<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="border" border="1" rules="all"><caption>Table 1. Socket design applications</caption><thead align="left"><tr><th valign="top" width="33.33333333333333%" id="d0e28">Recommendation</th>
|
|
<th valign="top" width="33.33333333333333%" id="d0e30">Reason</th>
|
|
<th valign="top" width="33.33333333333333%" id="d0e32">Best used in</th>
|
|
</tr>
|
|
</thead>
|
|
<tbody><tr><td valign="top" width="33.33333333333333%" headers="d0e28 ">Use asynchronous I/O</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 ">Asynchronous I/O used in a threaded server model is
|
|
preferable over the more conventional select() model.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Socket server applications which handle numerous
|
|
concurrent clients.</td>
|
|
</tr>
|
|
<tr><td valign="top" width="33.33333333333333%" headers="d0e28 ">When using asynchronous I/O, adjust the number of threads
|
|
in the process to an optimum number for the number of clients to be processed.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 ">If too few threads are defined then some clients might
|
|
time out before being handled. If too many threads are defined then some system
|
|
resource are not used efficiently. <div class="note"><span class="notetitle">Note:</span> It is better to have too many
|
|
threads than too few threads. </div>
|
|
</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Socket applications using asynchronous I/O. </td>
|
|
</tr>
|
|
<tr><td valign="top" width="33.33333333333333%" headers="d0e28 ">Design socket application to avoid the use of the postflag
|
|
on all start operations for asynchronous I/O.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 ">Avoids the performance overhead of transition to a completion
|
|
port if the operation has already been satisfied synchronously.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Socket applications using asynchronous I/O. </td>
|
|
</tr>
|
|
<tr><td valign="top" width="33.33333333333333%" headers="d0e28 ">Use <span class="apiname">send()</span> and <span class="apiname">recv()</span> over <span class="apiname">read()</span> and <span class="apiname">write()</span>.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 "><span class="apiname">send()</span> and <span class="apiname">recv()</span> APIs
|
|
provide a small performance and serviceability improvement over <span class="apiname">read()</span> and <span class="apiname">write()</span>.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Any socket program that knows it uses a socket descriptor
|
|
and not a file descriptor.</td>
|
|
</tr>
|
|
<tr><td valign="top" width="33.33333333333333%" headers="d0e28 ">Use the receive low water (SO_RCVLOWAT) socket option
|
|
to avoid looping on a receive operation until all data has arrived. </td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 ">Allows your application to wait for a minimum amount
|
|
of data to be received on the socket before satisfying a blocked receive operation.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Any socket application that receives data</td>
|
|
</tr>
|
|
<tr><td valign="top" width="33.33333333333333%" headers="d0e28 ">Use the MSG_WAITALL flag to avoid looping on a receive
|
|
operation until all data has arrived.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 ">Allows your application to wait for the entire buffer
|
|
provided on the receive operation to be received before satisfying a blocked
|
|
receive operation.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Any socket application that receives data and knows
|
|
in advance how much it expects to arrive.</td>
|
|
</tr>
|
|
<tr><td valign="top" width="33.33333333333333%" headers="d0e28 ">Use <span class="apiname">sendmsg()</span> and <span class="apiname">recvmsg()</span> over <span class="apiname">givedescriptor()</span> and <span class="apiname">takedescriptor()</span>.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 ">See <a href="cdescriptors.htm#cdescriptors">Descriptor passing between processes—sendmsg() and recvmsg()</a> for
|
|
the advantages. </td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Any socket application passing socket or file descriptors
|
|
between processes. </td>
|
|
</tr>
|
|
<tr><td valign="top" width="33.33333333333333%" headers="d0e28 ">When using <span class="apiname">select()</span>, try to avoid
|
|
a large number of descriptors in the read, write or exception set. <div class="note"><span class="notetitle">Note:</span> If
|
|
you have a large number of descriptors being used for <span class="apiname">select()</span> processing
|
|
see the asynchronous I/O recommendation above.</div>
|
|
</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 ">When there are a large number of descriptors in a read,
|
|
write or exception set, considerable redundant work occurs each time <span class="apiname">select()</span> is
|
|
called. As soon as a <span class="apiname">select()</span> is satisfied the actual socket
|
|
function must still be done, that is, a read or write or accept must still
|
|
be performed. Asynchronous I/O APIs combine the notification that something
|
|
has occurred on a socket with the actual I/O operation.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Applications that have a large(> 50) number of
|
|
descriptors active for <span class="apiname">select()</span>. </td>
|
|
</tr>
|
|
<tr><td valign="top" width="33.33333333333333%" headers="d0e28 ">Save your copy of the read, write and exception sets
|
|
before using <span class="apiname">select()</span> to avoid rebuilding the sets for
|
|
every time you must reissue the <span class="apiname">select()</span>. </td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 ">This saves the overhead of rebuilding the read, write,
|
|
or exception sets every time you plan to issue the <span class="apiname">select()</span>.
|
|
</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Any socket application where you are using <span class="apiname">select()</span> with
|
|
a large number of socket descriptors enabled for read, write or exception
|
|
processing. </td>
|
|
</tr>
|
|
<tr><td valign="top" width="33.33333333333333%" headers="d0e28 ">Do not use <span class="apiname">select()</span> as a timer. Use <span class="apiname">sleep()</span> instead.
|
|
<div class="note"><span class="notetitle">Note:</span> If granularity of the <span class="apiname">sleep()</span> timer
|
|
is not adequate, you might need to use <span class="apiname">select()</span> as a timer.
|
|
In this case, set maximum descriptor to 0 and the read, write, and exception
|
|
set to NULL.</div>
|
|
</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 ">Better timer response and less system overhead.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Any socket application where you are using <span class="apiname">select()</span> just
|
|
as a timer. </td>
|
|
</tr>
|
|
<tr><td valign="top" width="33.33333333333333%" headers="d0e28 ">If your socket application has increased the maximum
|
|
number of file and socket descriptors allowed per process using DosSetRelMaxFH()
|
|
and you are using <span class="apiname">select()</span> in this same application, be
|
|
careful of the affect this new maximum value has on the size of the read,
|
|
write and exception sets used for <span class="apiname">select()</span> processing. </td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 ">If you allocate a descriptor outside the range of the
|
|
read, write or exception set, as specified by FD_SETSIZE, then you can overwrite
|
|
and destroy storage. Ensure your set sizes are at least large enough to handle
|
|
whatever the maximum number of descriptors are set for the process and the
|
|
maximum descriptor value specified on the <span class="apiname">select()</span> API.
|
|
</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Any application or process where you use DosSetRelMaxFH()
|
|
and <span class="apiname">select()</span>. </td>
|
|
</tr>
|
|
<tr><td valign="top" width="33.33333333333333%" headers="d0e28 ">Set all socket descriptors in the read or write sets
|
|
to nonblocking. When a descriptor becomes enabled for read or write, loop
|
|
and consume or send all of the data until EWOULDBLOCK is returned. </td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 ">This allows you to minimize the number of <span class="apiname">select()</span> calls
|
|
when data is still available to be processed or read on a descriptor. </td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Any socket application where you are using <span class="apiname">select()</span>.</td>
|
|
</tr>
|
|
<tr><td valign="top" width="33.33333333333333%" headers="d0e28 ">Only specify the sets that you need to use for <span class="apiname">select()</span> processing.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 ">Most applications do not need to specify the exception
|
|
set or write set.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Any socket application where you are using <span class="apiname">select()</span>.</td>
|
|
</tr>
|
|
<tr><td valign="top" width="33.33333333333333%" headers="d0e28 "><p>Use GSKit APIs instead of SSL_APIs.</p>
|
|
</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 "><p>Both the Global Secure Toolkit (GSKit)
|
|
and i5/OS™ SSL_
|
|
APIs allow you to develop secure AF_INET or AF_INET6, SOCK_STREAM socket applications.
|
|
Because the GSKit APIs are supported across IBM<sup>®</sup> systems, they are the preferred APIs
|
|
to secure an application. The SSL_ APIs only exist in the i5/OS operating
|
|
system.</p>
|
|
</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Any socket application which needs to be enabled
|
|
for SSL/TLS processing.</td>
|
|
</tr>
|
|
<tr><td valign="top" width="33.33333333333333%" headers="d0e28 ">Avoid using signals.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 ">The performance overhead of signals (on all platforms,
|
|
not just the iSeries™)
|
|
is expensive. It is better to design your socket application to use Asynchronous
|
|
I/O or <span class="apiname">select()</span> APIs.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Any programmer considering the use of signals in
|
|
their socket application. </td>
|
|
</tr>
|
|
<tr><td valign="top" width="33.33333333333333%" headers="d0e28 ">Use protocol independent routines when available, such
|
|
as <span class="apiname">inet_ntop()</span>, <span class="apiname">inet_pton()</span>, <span class="apiname">getaddrinfo()</span>,
|
|
and <span class="apiname">getnameinfo()</span>.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 ">Even if you are not yet ready to support IPv6, use these
|
|
APIs, (instead of <span class="apiname">inet_ntoa()</span>, <span class="apiname">inet_addr()</span>, <span class="apiname">gethostbyname()</span> and <span class="apiname">gethostbyaddr</span>()) to prepare you for easier migration.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Any AF_INET or AF_INET6 application that uses network
|
|
routines.</td>
|
|
</tr>
|
|
<tr><td valign="top" width="33.33333333333333%" headers="d0e28 ">Use sockaddr_storage to declare storage for any address
|
|
family address.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e30 ">Simplifies writing code portable across multiple address
|
|
families and platforms. Declares enough storage to hold the largest address
|
|
family and ensures the correct boundary alignment.</td>
|
|
<td valign="top" width="33.33333333333333%" headers="d0e32 ">Any socket application that stores addresses.</td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div>
|
|
<div class="familylinks">
|
|
<div class="parentlink"><strong>Parent topic:</strong> <a href="rzab6soxoverview.htm" title="A socket is a communications connection point (endpoint) that you can name and address in a network.">Socket programming</a></div>
|
|
</div>
|
|
<div class="relconcepts"><strong>Related concepts</strong><br />
|
|
<div><a href="asynchi0.htm" title="Asynchronous I/O APIs provide a method for threaded client server models to perform highly concurrent and memory efficient I/O.">Asynchronous I/O</a></div>
|
|
</div>
|
|
<div class="relref"><strong>Related reference</strong><br />
|
|
<div><a href="xasynchi0.htm" title="An application creates an I/O completion port using the QsoCreateIOCompletionPort() API.">Example: Use asynchronous I/O</a></div>
|
|
<div><a href="xnonblock.htm" title="This sample program uses nonblocking and the select() API.">Example: Nonblocking I/O and select()</a></div>
|
|
<div><a href="xdescriptors.htm" title="The sendmsg() and recvmsg() examples show how to design a server program that uses these APIs to handle incoming connections.">Example: Pass descriptors between processes</a></div>
|
|
</div>
|
|
<div class="relinfo"><strong>Related information</strong><br />
|
|
<div><a href="../apis/dossrmfh.htm">DosSetRelMaxFH()</a></div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html> |