218 lines
11 KiB
HTML
218 lines
11 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<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))' />
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<meta name="DC.Type" content="reference" />
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<meta name="DC.Title" content="Example: Use signals with blocking socket APIs" />
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<meta name="abstract" content="Signals allow you to be notified when a process or application becomes blocked." />
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<meta name="description" content="Signals allow you to be notified when a process or application becomes blocked." />
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<meta name="DC.Relation" scheme="URI" content="example.htm" />
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<meta name="DC.Relation" scheme="URI" content="csignals.htm" />
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<meta name="DC.Relation" scheme="URI" content="asynchi0.htm" />
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<meta name="DC.Relation" scheme="URI" content="xasynchi0.htm" />
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<meta name="DC.Relation" scheme="URI" content="../apis/accept.htm" />
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<meta name="DC.Relation" scheme="URI" content="../apis/listen.htm" />
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<meta name="DC.Relation" scheme="URI" content="../apis/close.htm" />
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<meta name="DC.Relation" scheme="URI" content="../apis/socket.htm" />
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<meta name="DC.Relation" scheme="URI" content="../apis/bind.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 2001, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 2001, 2006" />
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<meta name="DC.Identifier" content="xsignals" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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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: Use signals with blocking socket APIs</title>
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</head>
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<body id="xsignals"><a name="xsignals"><!-- --></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: Use signals with blocking socket APIs</h1>
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<div><p>Signals allow you to be notified when a process or application
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becomes blocked.</p>
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<div class="section"><div class="p">Signals provide a time limit for blocking processes.
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In this example the signal occurs after five seconds on the <span class="apiname">accept()</span> call.
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This call normally blocks indefinitely, but because there is an alarm set,
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the call only blocks for five seconds. Because blocked programs can hinder
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performance of an application or server, they can be used to diminish this
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impact. The following example shows you how to use signals with blocking socket
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APIs. <div class="note"><span class="notetitle">Note:</span> Asynchronous I/O used in a threaded server model is preferable
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over the more conventional model. </div>
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</div>
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</div>
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<div class="section"><p><br /><img src="rzab6505.gif" alt="This graphic shows the socket calls that are used in the example program that uses signals." /><br /></p>
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</div>
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<div class="section"></div>
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<div class="section"><h4 class="sectiontitle">Socket flow of events: Use signals with blocking socket</h4><p>The
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following sequence of function calls shows how you can use signals to alert
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the application when the socket has been inactive:</p>
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<ol><li>The <span class="apiname">socket()</span> function returns a socket
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descriptor representing an endpoint. The statement also identifies that the
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AF_INET (Internet Protocol) address family with the TCP transport (SOCK_STREAM)
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being used for this socket. </li>
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<li>After the socket descriptor is created, a <span class="apiname">bind()</span> function
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gets a unique name for the socket. In this example, a port number is not specified
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because the client application does not connect to this socket. This code
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snippet can be used within other server programs that use blocking APIs, such
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as <span class="apiname">accept()</span>.</li>
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<li>The <span class="apiname">listen()</span> function indicates a willingness to accept
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client connection requests. After the <span class="apiname">listen()</span> function
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is issued, an alarm is set to go off in five seconds. This alarm or signal
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alerts you when the <span class="apiname">accept()</span> call blocks.</li>
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<li>The <span class="apiname">accept()</span> function accepts a client
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connection request. This call normally blocks indefinitely, but because there
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is an alarm set, the call only blocks for five seconds. When the alarm goes
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off, the accept call is completed with -1 and with an errno value
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of EINTR. </li>
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<li>The <span class="apiname">close()</span> function ends any open socket descriptors. </li>
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</ol>
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</div>
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<div class="section"><div class="note"><span class="notetitle">Note:</span> By using the code examples, you agree to the terms of the <a href="codedisclaimer.htm">Code license and disclaimer information</a>.</div>
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<pre>/******************************************************************/
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/* Example shows how to set alarms for blocking socket APIs */
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/******************************************************************/
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/******************************************************************/
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/* Include files */
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/******************************************************************/
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#include <signal.h>
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#include <unistd.h>
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#include <stdio.h>
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#include <time.h>
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#include <errno.h>
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#include <sys/socket.h>
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#include <netinet/in.h>
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/******************************************************************/
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/* Signal catcher routine. This routine will be called when the */
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/* signal occurs. */
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/******************************************************************/
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void catcher(int sig)
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{
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printf(" Signal catcher called for signal %d\n", sig);
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}
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/******************************************************************/
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/* Main program */
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/******************************************************************/
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int main(int argc, char *argv[])
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{
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struct sigaction sact;
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struct sockaddr_in addr;
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time_t t;
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int sd, rc;
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/******************************************************************/
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/* Create an AF_INET, SOCK_STREAM socket */
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/******************************************************************/
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printf("Create a TCP socket\n");
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sd = socket(AF_INET, SOCK_STREAM, 0);
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if (sd == -1)
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{
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perror(" socket failed");
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return(-1);
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}
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/******************************************************************/
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/* Bind the socket. A port number was not specified because */
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/* we are not going to ever connect to this socket. */
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/******************************************************************/
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memset(&addr, 0, sizeof(addr));
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addr.sin_family = AF_INET;
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printf("Bind the socket\n");
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rc = bind(sd, (struct sockaddr *)&addr, sizeof(addr));
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if (rc != 0)
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{
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perror(" bind failed");
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close(sd);
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return(-2);
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}
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/******************************************************************/
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/* Perform a listen on the socket. */
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/******************************************************************/
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printf("Set the listen backlog\n");
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rc = listen(sd, 5);
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if (rc != 0)
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{
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perror(" listen failed");
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close(sd);
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return(-3);
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}
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/******************************************************************/
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/* Set up an alarm that will go off in 5 seconds. */
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/******************************************************************/
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printf("\nSet an alarm to go off in 5 seconds. This alarm will cause the\n");
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printf("blocked accept() to return a -1 and an errno value of EINTR.\n\n");
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sigemptyset(&sact.sa_mask);
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sact.sa_flags = 0;
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sact.sa_handler = catcher;
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sigaction(SIGALRM, &sact, NULL);
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alarm(5);
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/******************************************************************/
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/* Display the current time when the alarm was set */
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/******************************************************************/
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time(&t);
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printf("Before accept(), time is %s", ctime(&t));
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/******************************************************************/
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/* Call accept. This call will normally block indefinitely, */
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/* but because we have an alarm set, it will only block for */
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/* 5 seconds. When the alarm goes off, the accept call will */
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/* complete with -1 and an errno value of EINTR. */
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/******************************************************************/
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errno = 0;
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printf(" Wait for an incoming connection to arrive\n");
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rc = accept(sd, NULL, NULL);
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printf(" accept() completed. rc = %d, errno = %d\n", rc, errno);
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if (rc >= 0)
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{
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printf(" Incoming connection was received\n");
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close(rc);
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}
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else
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{
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perror(" errno string");
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}
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/******************************************************************/
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/* Show what time it was when the alarm went off */
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/******************************************************************/
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time(&t);
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printf("After accept(), time is %s\n", ctime(&t));
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close(sd);
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return(0);
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}</pre>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="example.htm" title="These examples provide many sample programs that illustrate the more advanced socket concepts. You can use these sample programs to create your own applications that complete a similar task.">Examples: Socket application designs</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="csignals.htm" title="An application program can request to be notified asynchronously (request that the system send a signal) when a condition that the application is interested in occurs.">Signals</a></div>
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<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>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<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>
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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/accept.htm">accept()</a></div>
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<div><a href="../apis/listen.htm">listen()</a></div>
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<div><a href="../apis/close.htm">close()</a></div>
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<div><a href="../apis/socket.htm">socket()</a></div>
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<div><a href="../apis/bind.htm">bind()</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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