author | hgs |
Mon, 04 Oct 2010 11:29:25 +0300 | |
changeset 78 | 71ad690e91f5 |
parent 21 | 2a9601315dfc |
permissions | -rw-r--r-- |
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Revision: v2.1.22
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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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Revision: v2.1.22
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Runtime Support hides differences between different runtime implementations |
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Revision: v2.1.22
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from the API developer. |
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Revision: v2.1.22
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<p> |
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Revision: v2.1.22
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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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Revision: v2.1.22
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eRCP Runtime) have different implementations of Runtime support API, but |
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Revision: v2.1.22
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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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Revision: v2.1.22
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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> |