135 lines
9.1 KiB
HTML
135 lines
9.1 KiB
HTML
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<!DOCTYPE html
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<meta name="DC.Title" content="Example: Pass descriptors between processes" />
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<meta name="abstract" content="The sendmsg() and recvmsg() examples show how to design a server program that uses these APIs to handle incoming connections." />
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Example: Pass descriptors between processes</title>
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</head>
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<body id="xdescriptors"><a name="xdescriptors"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Example: Pass descriptors between processes</h1>
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<div><p>The <span class="apiname">sendmsg()</span> and <span class="apiname">recvmsg()</span> examples
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show how to design a server program that uses these APIs to handle incoming
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connections.</p>
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<div class="section"><p>When the server starts, it creates a pool of worker jobs. These
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preallocated (spawned) worker jobs wait until needed. When the client job
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connects to the server, the server gives the incoming connection to one of
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the worker jobs.</p>
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</div>
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<div class="section"><p>The following figure illustrates how the server, worker, and client
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jobs interact when the system uses the <span class="apiname">sendmsg()</span> and <span class="apiname">recvmsg()</span> server
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design. <br /><img src="rxab6507.gif" alt="Server, worker, and client job interaction when you use the sendmsg() and recvmsg() server design." /><br /></p>
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</div>
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<div class="section"><h4 class="sectiontitle">Flow of socket events: Server that uses <span class="apiname">sendmsg()</span> and <span class="apiname">recvmsg()</span> functions</h4><p>The
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following sequence of the socket calls provides a description of the graphic.
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It also describes the relationship between the server and worker examples.
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The first example uses the following socket calls to create a child process
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with the <span class="apiname">sendmsg()</span> and <span class="apiname">recvmsg() </span> function
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calls:</p>
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<ol><li>The <span class="apiname">socket()</span> function returns a socket descriptor representing
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an endpoint. The statement also identifies that the INET (Internet Protocol)
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address family with the TCP transport (SOCK_STREAM) are used for this socket.</li>
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<li>After the socket descriptor is created, the <span class="apiname">bind()</span> function
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gets a unique name for the socket. </li>
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<li>The <span class="apiname">listen()</span> allows the server to accept incoming client
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connections. </li>
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<li> The <span class="apiname">socketpair()</span> function creates a pair of UNIX<sup>®</sup> datagram
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sockets. A server can use the <span class="apiname">socketpair()</span> API to create
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a pair of AF_UNIX sockets.</li>
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<li>The <span class="apiname">spawn()</span> function initializes the parameters
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for a work job to handle incoming requests. In this example, the child job
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created inherits the socket descriptor that was created by the <span class="apiname">socketpair()</span>.</li>
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<li>The server uses the <span class="apiname">accept()</span> function to accept an
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incoming connection request. The <span class="apiname">accept()</span> call blocks indefinitely
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waiting for the incoming connection to arrive.</li>
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<li>The <span class="apiname">sendmsg()</span> function sends an incoming connection
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to one of the worker jobs. The child process accepts the connection with the<span class="apiname">recvmsg()</span> function.
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The child job is not active when the server called <span class="apiname">sendmsg()</span>.</li>
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<li>In this example, the first <span class="apiname">close()</span> function closes
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the accepted socket. The second <span class="apiname">close ()</span> call ends the
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listening socket.</li>
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</ol>
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</div>
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<div class="section"><h4 class="sectiontitle">Socket flow of events: Worker job that uses <span class="apiname">recvmsg()</span></h4><p>The
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second example uses the following sequence of function calls:</p>
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<ol><li>After the server has accepted a connection and passed its socket descriptor
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to the worker job, the <span class="apiname">recvmsg()</span> function receives the
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descriptor. In this example, the <span class="apiname">recvmsg()</span> function waits
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until the server sends the descriptor.</li>
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<li>The <span class="apiname">recv()</span> function receives a message from the client.
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</li>
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<li>The <span class="apiname">send()</span> function echoes data back to the client.</li>
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<li>The <span class="apiname">close()</span> function ends the worker job.</li>
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</ol>
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</div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="x1descriptors.htm">Example: Server program used for sendmsg() and recvmsg()</a></strong><br />
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This example shows how to use the <span class="apiname">sendmsg()</span> API
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to create a pool of worker jobs.</li>
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<li class="ulchildlink"><strong><a href="x2descriptors.htm">Example: Worker program used for sendmsg() and recvmsg()</a></strong><br />
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This example shows how to use the <span class="apiname">recvmsg()</span> API
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client job to receive the worker jobs.</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="xcodesigns.htm" title="There are a number of ways that you can design a connection-oriented socket server on the iSeries. These example programs can be used to create your own connection-oriented designs.">Examples: Connection-oriented designs</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="cdescriptors.htm" title="The ability to pass an open descriptor between jobs can lead to a new way of designing client/server applications.">Descriptor passing between processes—sendmsg() and recvmsg()</a></div>
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<div><a href="designrec.htm" title="Before working with socket applications, assess the functional requirements, goals, and needs of the socket application.">Socket application design recommendations</a></div>
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<div><a href="generic.htm" title="This code example contains the code for a common client job.">Example: Generic client</a></div>
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</div>
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<div class="relinfo"><strong>Related information</strong><br />
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<div><a href="../apis/spawn.htm">spawn()</a></div>
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<div><a href="../apis/bind.htm">bind()</a></div>
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<div><a href="../apis/socket.htm">socket()</a></div>
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<div><a href="../apis/listen.htm">listen()</a></div>
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<div><a href="../apis/accept.htm">accept()</a></div>
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<div><a href="../apis/close.htm">close()</a></div>
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<div><a href="../apis/socketp.htm">socketpair()</a></div>
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<div><a href="../apis/sendms.htm">sendmsg()</a></div>
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<div><a href="../apis/recvms.htm">recvmsg()</a></div>
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<div><a href="../apis/send.htm">send()</a></div>
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<div><a href="../apis/recv.htm">recv()</a></div>
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</div>
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</div>
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</body>
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</html>
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