174 lines
6.9 KiB
HTML
174 lines
6.9 KiB
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="Copyright" content="Copyright (c) 2006 by IBM Corporation">
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<title>Unhandled exceptions terminate the thread (not the process)</title>
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<!-- Begin Header Records ========================================== -->
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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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<!-- RCHVMW2 on 29 Jan 1999 at 10:01:37 -->
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<!--File Edited November 2001 -->
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<!--End Header Records -->
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<link rel="stylesheet" type="text/css" href="../rzahg/ic.css">
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</head>
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<body>
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<!-- Java sync-link -->
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<script language="Javascript" src="../rzahg/synch.js" type="text/javascript">
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</script>
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<a name="Top_Of_Page"></a>
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<h2>Unhandled exceptions terminate the thread (not the process)</h2>
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<p>On a UNIX system, when an invalid or illegal software condition is
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encountered (such as dividing by zero or using an invalid pointer), a signal is
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generated. If the signal is not handled, the process is terminated.</p>
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<p>The operating system does not generate a signal for these events, but instead, generates
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an exception message. The exception message moves up the call stack,
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allowing each stack frame (function on the stack or invocation entry) a chance
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to handle the exception. Each function invocation may choose to handle or not
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to handle the exception. If the exception is not handled, the message continues
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to the next stack frame.</p>
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<p>When the exception message reaches certain boundaries on the call stack
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(like a main() entry point, usually called control boundaries) certain events
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take place. These events include changing the exception to a different type,
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terminating the process, terminating the activation group, or terminating the
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thread. If an unhandled exception condition happens in a secondary thread and
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moves all the way to the first invocation in the thread without being handled,
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the resulting action will be to terminate the thread. During this percolation,
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if the exception hits a control boundary and is not handled, it may terminate
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the process.</p>
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<p>A signal is never automatically generated for an exception message. When an
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unhandled exception terminates the thread, Pthread cancellation cleanup
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handlers and Pthread data destructors do not run and the thread is terminated
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immediately with a return status of <strong>PTHREAD_EXCEPTION_NP</strong>.
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<strong>PTHREAD_EXCEPTION_NP</strong> is a macro similar to the <strong>
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PTHREAD_CANCELED</strong> macro, and is not NULL or a valid pointer.</p>
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<p>On a UNIX system, this same activity may terminate the process due to the
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signal that is generated.</p>
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<p>In order to have your application terminate the process, when the exception
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occurs, you must handle it and explicitly terminate the process. The following
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example handles all hardware exceptions using the ANSI C signal model and uses
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the Pthread signal SIGABRT to terminate the process.</p>
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<p>You can also turn the exception message into a Posix signal and it may be
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handled. See <a href="concep31.htm">Exceptions vs. Asynchronous signals vs.
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ANSI C signals</a> for more information.</p>
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<br>
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<h3>Example</h3>
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<p>See <a href="../apiref/aboutapis.htm#codedisclaimer">Code disclaimer information</a>
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for information pertaining to code examples.</p>
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<pre>
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#define _MULTI_THREADED
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#include <stdio.h>
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#include <qp0z1170.h>
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#include <time.h>
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#include <signal.h>
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#include <pthread.h>
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#include "check.h"
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void abortTheProcessWhenAnExceptionOccurs(int sigNumber);
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void *threadfunc1(void *parm);
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void *threadfunc1(void *parm)
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{
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char *p=NULL;
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printf("Thread1: Unhandled exception (pointer fault) about to happen\n");
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*p = `!';
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printf("Thread1: After exception\n");
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return NULL;
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}
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void abortTheProcessWhenAnExceptionOccurs(int sigNumber) {
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/* In a multithreaded environment this is a little difficult. We have to */
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/* re-enable the ANSI C handler immediately, because that is the way it */
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/* is defined. (A better alternative may be direct monitor exception */
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/* handlers that are always valid in the function which they are */
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/* registered, and with direct monitors, we can catch the hardware */
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/* exception before it is converted to an ANSI C signal */
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signal(SIGALL, abortTheProcessWhenAnExceptionOccurs);
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/* Since ANSI C signals and hardware exceptions are only handled in */
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/* the same thread that caused them, we send the Posix signal to */
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/* the calling thread (The signal is delivered before returning from */
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/* pthread_kill(). */
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printf("Mapping ANSI signal %d to posix signal SIGABRT. "
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"Aborting the process\n", sigNumber);
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/* If we want to do some debug processing, we can put it here. */
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pthread_kill(pthread_self(), SIGABRT);
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return;
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}
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int main(int argc, char **argv)
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{
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int rc=0;
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pthread_t threadid;
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void *status;
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printf("----------- Setup Signal Mapping/Handling -------------\n");
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printf("- Register ANSI C signal handler to map ALL\n"
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" ANSI C signals & hardware exceptions to Posix signals\n");
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/* If we want to do debug, or determine what when wrong a little more easily,
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*/
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/* we could use the abortTheProcessWhenAnExceptionOccurs function to delay
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the thread, or */
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/* dump failure data of some sort.
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*/
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signal(SIGALL, abortTheProcessWhenAnExceptionOccurs);
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printf("----------- Start memory fault thread -------------\n");
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printf("Create a thread\n");
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rc = pthread_create(&threadid, NULL, threadfunc1, NULL);
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checkResults("pthread_create()\n", rc);
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rc = pthread_join(threadid, &status);
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checkResults("pthread_join()\n", rc);
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printf("Main completed\n");
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return 0;
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}
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</pre>
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<p><strong>Output:</strong></p>
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<pre>
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----------- Setup Signal Mapping/Handling -------------
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- Register ANSI C signal handler to map ALL
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ANSI C signals & hardware exceptions to Posix signals
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----------- Start memory fault thread -------------
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Create a thread
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Thread1: Unhandled exception (pointer fault) about to happen
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Mapping ANSI signal 5 to posix signal SIGABRT. Aborting the process
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</pre>
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<hr>
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<center>
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<table cellpadding="2" cellspacing="2">
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<tr align="center">
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<td valign="middle" align="center">
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<a href="#Top_Of_Page">Top</a> |
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<a href="rzah4mst.htm">Pthread APIs</a> |
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<a href="aplist.htm">APIs by category</a></td>
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</tr>
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</table>
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</center>
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</body>
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</html>
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