105 lines
6.5 KiB
HTML
105 lines
6.5 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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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="security" content="public" />
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<meta name="Robots" content="index,follow" />
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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="concept" />
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<meta name="DC.Title" content="Java native methods and threads considerations" />
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<meta name="abstract" content="You can use native methods to access functions that are not available in Java. To better use Java with native methods, you need to understand these concepts." />
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<meta name="description" content="You can use native methods to access functions that are not available in Java. To better use Java with native methods, you need to understand these concepts." />
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<meta name="DC.Relation" scheme="URI" content="jni.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="nmthread" />
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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>Java native methods and threads considerations</title>
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</head>
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<body id="nmthread"><a name="nmthread"><!-- --></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">Java native methods and threads considerations</h1>
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<div><p>You can use native methods to access functions that are not available
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in Java™.
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To better use Java with native methods, you need to understand these
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concepts.</p>
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<ul><li>A Java thread,
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whether created by Java or an attached native thread, has all
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floating point exceptions disabled. If the thread runs a native method that
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reenables floating point exceptions, Java does not turn them off a second time.
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If the user application does not disable them before returning to run Java code,
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then the Java code may not behave correctly if a floating point
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exception occurs. When a native thread detaches from the Java virtual
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machine, its floating point exception mask is restored to the value that was
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in effect when it was attached.</li>
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<li>When a native thread attaches to the Java virtual machine, the Java virtual
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machine changes the threads priority, if necessary, to conform to the one
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to ten priority schemes that Java defines. When the thread detaches,
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the priority is restored. After attaching, the thread can change the thread
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priority by using a native method interface (for example, a POSIX API). Java does
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not change the thread priority on transitions back to the Java virtual
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machine.</li>
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<li>The Invocation API component of the Java Native Interface (JNI) permits a user
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to embed a Java virtual machine within their application. If an
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application creates a Java virtual machine and the Java virtual
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machine ends abnormally, the MCH74A5 "Java Virtual Machine Terminated" iSeries™ exception
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is signalled to the initial thread of the process if that thread was attached
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to the Java virtual machine when the Java virtual
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machine ended. The Java virtual machine could end abnormally
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for any of these reasons: <ul><li>The user calls the java.lang.System.exit() method.</li>
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<li>A thread that the Java virtual machine requires ends.</li>
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<li>An internal error occurs in the Java virtual machine.</li>
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</ul>
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This behavior differs from most other Java platforms. On most other platforms,
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the process that automatically creates the Java virtual machine ends abruptly as soon
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as the Java virtual machine ends. If the application monitors
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and handles a signalled MCH74A5 exception, it may continue to run. Otherwise,
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the process ends when the exception goes unhandled. By adding the code that
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deals with the iSeries server-specific
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MCH74A5 exception, you can make the application less portable to other platforms.</li>
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</ul>
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<p>Because native methods always run in a multithreaded process, the code
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that they contain must be thread safe. This places these restrictions on the
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languages and functions that are used for native methods:</p>
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<ul><li>You should not use ILE CL for native methods, because this language is
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not thread safe. To run thread safe CL commands, you can use the C language
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system() function or the java.lang.Runtime.exec() method. <ul><li>Use the C language system() function to run thread safe CL commands from
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within a C or C++ native method.</li>
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<li>Use the java.lang.Runtime.exec() method to run thread safe CL commands
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directly from Java.</li>
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</ul>
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</li>
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<li>You can use ILE C, ILE C++, ILE COBOL, and ILE RPG to write a native method,
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but all of the functions that are called from within the native method must
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be thread safe. <p><strong>Note:</strong> Compile-time support for writing native methods
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is currently only supplied for the C, C++, and RPG languages. While possible,
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writing native methods in other languages may be much more complicated.</p>
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<p><strong>Caution: <em>Not
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all standard C, C++, COBOL, or RPG functions are thread safe.</em></strong></p>
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</li>
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<li>The C and C++ exit() and abort() functions should never be used within
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a native method. These functions cause the entire process that runs the Java virtual
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machine to stop. This includes all of the threads in the process, regardless
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of if they were originated by Java or not. <div class="note"><span class="notetitle">Note:</span> The exit() function
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referred to is the C and C++ function, and is not the same as the java.lang.Runtime.exit()
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method.</div>
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</li>
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</ul>
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<p>For more information about threads on the iSeries server, see <a href="../rzahw/rzahwovepo.htm" target="_blank">Multithreaded applications</a>. </p>
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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="jni.htm" title="You should only use native methods in cases where pure Java cannot meet your programming needs.">Use the Java Native Interface for native methods</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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