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javacommons/utils/javasrc/com/nokia/mj/impl/rt/support/package.html
author hgs
Mon, 04 Oct 2010 11:29:25 +0300
changeset 78 71ad690e91f5
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permissions -rw-r--r--
v2.2.17_1
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<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
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<html>
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<head>
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   <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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   <meta name="Author" content="Nokia">
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   <title>Runtime support API</title>
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</head>
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<body>
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Runtime Support hides differences between different runtime implementations
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from the API developer.
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<p>
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Runtime Support aligns different runtimes (including different JVMs so that
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API implementations can rely on them in all runtimes (MIDP3 Runtime, CDC main,
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eRCP Runtime) have different implementations of Runtime support API, but
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runtime differences are hidden behind Runtime support API. Runtime Support also
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provides API for hiding differences between different JVM vendors and for
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hiding some differnces between CLDC and CDC.
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<p>
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Runtime Support provides following services:
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<li>Application related services.</li>
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<li>Special services provided by the JVM.</li>
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<li>System property extension mechanism.</li>
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<p>
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<h2>Application related services</h2>
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Application related services provides utilities for getting application specific
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static information like name, uid, vendor, version etc. Application related
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services provides also some utilities that are application lifetime dependent
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like ability receive a notification when the application is about to close.
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<p>
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For further details see {@link com.nokia.mj.impl.rt.support.ApplicationInfo}
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or {@link com.nokia.mj.impl.rt.support.ApplicationUtils}.
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<h2>JVM services</h2>
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The basic idea is to provide helper utilities for cases where there is need to
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use different implementation depending on the used JVM or the used configuration.
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In other words the underlying JVM is tried to hide from the API developer.
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<p>
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There are two cases where port layer is needed:
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<li>Some standard API either is used differently or is missing from certain
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configuration. This is most commonly needed to hide differences between CDC
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and CLDC. For example System.loadLibrary doesn't exist in the CLDC and
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therefore when using CLDC JVM we need to call some proprietary API provided by
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the JVM vendor, which must be hidden from the API developers. Another example
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is Class.forName. If the we are using CDC JVM and we are trying to load a class
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which is int 'normal' classpath from a class that is in the bootclass path,
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we need to provide the class loader. In CLDC we don't have class loaders, so
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the Runtime support variates the usage of Class.forName in different
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configurations.</li>
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<li>The JVM provides some proprietary APIs to do some things in more
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advanced/faster way than it is possible using the standard Java APIs. One
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example could be {@link com.nokia.mj.impl.rt.support.NativeMemoryBlock}, which
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provides a way to read some resource from the jar file and store the content
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in a native memory block instead of copying the content to Java side.
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<p>
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JVM services are divided into two different classes:
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{@link com.nokia.mj.impl.rt.support.Jvm} and
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{@link com.nokia.mj.impl.rt.support.JvmInternal}. <code>Jvm</code> is meant
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for all API developers while <code>JvmInternal</code> is meant only for
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Runtime's internal usage.
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<h3>Finalizers</h3>
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Some public API are defined so that implementation requires usage of
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Java finalization feature. Since finalization is not part of CLDC, the
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Runtime Support provides a common way to hide VM specific implemetation from
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the API developer. The provided way works also in case where the used
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configuration (e.g. CDC) officially supports finalization.
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<p>
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For further details see {@link com.nokia.mj.impl.rt.support.Finalizer}.
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<h2>System property extension mechanism</h2>
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Many APIs need to introduce new system properties into the system. Since the
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JVM is delivered in binary format, it is needed a mechanism to extend
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(and overwrite) existing system properties.
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<p>
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System properties can be divided into three categories:
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<li>Static ones, that will never change during the runtime of the JVM (e.g.
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microedition.jtwi.version).</li>
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<li>Dynamic static ones, that will be solved during first query, but will
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not change after that during the runtime of the JVM
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(e.g. microedition.platform).</li>
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<li>Dynamic ones, that may change any time during the runtime of the JVM
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(e.g. com.nokia.memoryramfree)</li>
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<p>
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No matter which category the system property belongs to, it is stored into
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the hash table from where it can be found fast. Only the value of the property
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tells if the property is static or dynamic.
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<p>
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The usage of System property extension mechanism is explained in more detailed
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in {@link com.nokia.mj.impl.rt.support.SystemPropertyProvider here}.
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<h2>Runtime Support wiki pages</h2>
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Here is a link to the Wiki pages of the
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<a href="http://wikis.in.nokia.com/MIDPEvolution/ArchitectureRuntimeSupport"
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target="_top">Runtime Support</a>.
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</body>
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</html>
FCL/sf/app/jrt