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125 lines
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<title>Invocation API functions</title>
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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">Invocation API functions</h1>
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<div><p>The IBM<sup>®</sup> Developer
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Kit for Java™ supports these Invocation API functions.</p>
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<div class="section"><div class="note"><span class="notetitle">Note:</span> Before using this API, you must ensure that you are in a multithread-capable
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job. See <a href="../rzahw/rzahwovepo.htm" target="_blank">Multithreaded applications</a> for more information about
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multithread-capable jobs. </div>
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<ul><li><strong>JNI_GetCreatedJavaVMs</strong> <p>Returns information about all Java virtual
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machines that were created. Even though this API is designed to return information
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for multiple Java virtual machines (JVMs), only one JVM can exist
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for a process. Therefore, this API will return a maximum of one JVM.</p>
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<p>Signature:</p>
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<pre> jint JNI_GetCreatedJavaVMs(JavaVM **vmBuf,
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jsize bufLen,
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jsize *nVMs);</pre>
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<p>vmBuf is an output area whose size is determined by bufLen,
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which is the number of pointers. Each Java virtual machine has an associated JavaVM
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structure that is defined in java.h. This API stores a pointer to the JavaVM
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structure that is associated with each created Java virtual machine into vmBuf, unless
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vmBuf is 0. Pointers to JavaVM structures are stored in the order of the corresponding Java virtual
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machines that are created. nVMs returns the number of virtual machines
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that are currently created. Your iSeries™ server supports the creation
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of more than one Java virtual machine, so you may expect a value higher
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than one. This information, along with the size of the vmBuf, determines whether
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pointers to JavaVM structures for each created Java virtual machine are returned.</p>
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</li>
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<li><strong>JNI_CreateJavaVM</strong> <p>Allows you to create a Java virtual
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machine and subsequently use it in an application.</p>
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<p>Signature:</p>
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<blockquote> <pre>jint JNI_CreateJavaVM(JavaVM **p_vm,
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void **p_env,
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void *vm_args);</pre>
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</blockquote>
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<p>p_vm is the address of a JavaVM pointer for
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the newly created Java virtual machine. Several other JNI Invocation APIs
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use p_vm to identify the Java virtual machine. p_env is the address
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of a JNI Environment pointer for the newly created Java virtual machine. It points to a table
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of JNI functions that start those functions. vm_args is a structure that contains Java virtual
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machine initialization parameters.</p>
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<p>If you start a Run Java (RUNJVA)
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command or JAVA command and specify a property that has an equivalent command
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parameter, then the command parameter takes precedence. The property is ignored.
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For example, the os400.optimization parameter is ignored in this command:</p>
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<blockquote> <pre>JAVA CLASS(Hello) PROP((os400.optimization 0))</pre>
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</blockquote>
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<p>For a list of 0S/400 unique properties that
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are supported by the JNI_CreateJavaVM API, see <a href="sysprop.htm">Java system
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properties</a>.</p>
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<div class="note"><span class="notetitle">Note:</span> Java on the iSeries server supports creating only
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one Java virtual
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machine (JVM) within a single job or process. For more information, see <a href="multjvm.htm">Support for multiple Java virtual machines</a></div>
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</li>
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<li><strong>DestroyJavaVM</strong> <p>Destroys the Java virtual machine.</p>
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<p>Signature:</p>
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<blockquote> <pre>jint DestroyJavaVM(JavaVM *vm)</pre>
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</blockquote>
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<p>When the Java virtual machine is created, vm is the
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JavaVM pointer that is returned.</p>
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</li>
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<li><strong>AttachCurrentThread</strong> <p>Attaches a thread to a Java virtual
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machine, so it can use Java virtual machine services.</p>
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<p>Signature:</p>
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<blockquote> <pre>jint AttachCurrentThread(JavaVM *vm,
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void **p_env,
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void *thr_args);</pre>
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</blockquote>
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<p>The JavaVM pointer, vm, identifies the Java virtual
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machine to which the thread is being attached. p_env is the pointer to the
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location where the JNI Interface pointer of the current thread is placed.
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thr_args contains VM specific thread attachment arguments.</p>
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</li>
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<li><strong>DetachCurrentThread</strong> <p>Signature:</p>
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<blockquote> <pre>jint DetachCurrentThread(JavaVM *vm);</pre>
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</blockquote>
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<p>vm identifies the Java virtual machine from which the thread
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is being detached.</p>
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</li>
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</ul>
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<p>For a complete description of the Invocation API functions, refer
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to the <a href="javaapi/guide/jni/index.html" target="_blank">Java Native
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Interface Specification by Sun Microsystems, Inc.</a>, or <a href="http://www.java.sun.com/" target="_blank">The Source for Java Technology
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java.sun.com</a>.</p>
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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="invocapi.htm" title="The Invocation API, which is part of the Java Native Interface (JNI), allows non-Java code to create a Java virtual machine, and load and use Java classes. This function lets a multithreaded program make use of Java classes that are running in a single Java virtual machine in multiple threads.">Java Invocation API</a></div>
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</div>
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