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| <div class="subTitle"><span class="moduleLabelInType">Module</span> <a href="../../../../module-summary.html">openj9.sharedclasses</a></div> |
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| <h2 title="Interface SharedDataHelper" class="title">Interface SharedDataHelper</h2> |
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| <pre>public interface <span class="typeNameLabel">SharedDataHelper</span> |
| extends <a href="SharedHelper.html" title="interface in com.ibm.oti.shared">SharedHelper</a></pre> |
| <div class="block"><p>SharedDataHelper API that stores and finds byte data using String tokens.</p> |
| <h2>Description</h2> |
| <p>A SharedDataHelper is obtained by calling getSharedDataHelper(ClassLoader) on a SharedDataHelperFactory.</p> |
| <p>The SharedDataHelper allows byte data to be written into the shared class cache and shared with other VMs.</p> |
| <p>Byte data to be stored in the cache should exist in a java.nio.ByteBuffer which is copied to the cache when |
| storeSharedData() is called. The function returns a read-only java.nio.ByteBuffer which is the shared copy of the data. |
| Any subsequent changes to the ByteBuffer are therefore not reflected in the cache unless it is re-stored.</p> |
| <p>Byte data is found in the cache by calling findSharedData() which returns a read-only java.nio.ByteBuffer which |
| maps to the byte data that exists in the cache.</p> |
| <h2>Tokens</h2> |
| <p>A String token is chosen/generated by the application which is using the Helper and should ideally include a unique |
| identifier and some kind of versioning information. Eg. com.foo.myApp31_myDoozerData_003. The important factor is that |
| other VMs running the same application should be able to apply the same algorithm and find the data. </p> |
| <h2>Dynamic Cache Updates</h2> |
| <p>Since the shared cache is persistent beyond the lifetime of a JVM, data in the shared cache may become out-of-date (<q>stale</q>). |
| Using this helper, it is entirely the responsibility of the application to ensure that cache entries are kept up-to-date. |
| Tokens have no meaning to the cache, so effectively turn it into a dictionary of classes.</p> |
| <p>E.g. A token may be the location where the class was found, combined with some type of versioning data.</p> |
| <p>If an application stores multiple versions of the same data using the same token, only the most recent will be returned by findSharedData.</p></div> |
| <dl> |
| <dt><span class="seeLabel">See Also:</span></dt> |
| <dd><a href="SharedHelper.html" title="interface in com.ibm.oti.shared"><code>SharedHelper</code></a>, |
| <a href="SharedDataHelperFactory.html" title="interface in com.ibm.oti.shared"><code>SharedDataHelperFactory</code></a>, |
| <a href="SharedClassPermission.html" title="class in com.ibm.oti.shared"><code>SharedClassPermission</code></a></dd> |
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| <tr> |
| <th class="colFirst" scope="col">Modifier and Type</th> |
| <th class="colSecond" scope="col">Method</th> |
| <th class="colLast" scope="col">Description</th> |
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| <td class="colFirst"><code><a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/nio/ByteBuffer.html?is-external=true" title="class or interface in java.nio" class="externalLink" target="_blank">ByteBuffer</a></code></td> |
| <th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#findSharedData(java.lang.String)">findSharedData</a></span>​(<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/String.html?is-external=true" title="class or interface in java.lang" class="externalLink" target="_blank">String</a> token)</code></th> |
| <td class="colLast"> |
| <div class="block">Find data in the shared cache using a specific token.</div> |
| </td> |
| </tr> |
| <tr id="i1" class="rowColor"> |
| <td class="colFirst"><code><a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/nio/ByteBuffer.html?is-external=true" title="class or interface in java.nio" class="externalLink" target="_blank">ByteBuffer</a></code></td> |
| <th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="#storeSharedData(java.lang.String,java.nio.ByteBuffer)">storeSharedData</a></span>​(<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/String.html?is-external=true" title="class or interface in java.lang" class="externalLink" target="_blank">String</a> token, |
| <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/nio/ByteBuffer.html?is-external=true" title="class or interface in java.nio" class="externalLink" target="_blank">ByteBuffer</a> data)</code></th> |
| <td class="colLast"> |
| <div class="block">Store data in the shared cache using a specific token.</div> |
| </td> |
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| <h3>Methods declared in interface com.ibm.oti.shared.<a href="SharedHelper.html" title="interface in com.ibm.oti.shared">SharedHelper</a></h3> |
| <code><a href="SharedHelper.html#getClassLoader()">getClassLoader</a></code></li> |
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| <h3>Method Detail</h3> |
| <a id="findSharedData(java.lang.String)"> |
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| <h4>findSharedData</h4> |
| <pre class="methodSignature"><a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/nio/ByteBuffer.html?is-external=true" title="class or interface in java.nio" class="externalLink" target="_blank">ByteBuffer</a> findSharedData​(<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/String.html?is-external=true" title="class or interface in java.lang" class="externalLink" target="_blank">String</a> token)</pre> |
| <div class="block">Find data in the shared cache using a specific token.<p> |
| Data will be returned only for an exact String match of the token. Otherwise, null is returned.<br> |
| The ByteBuffer returned is read-only and cannot be modified.<br> |
| If a SecurityManager is installed, findSharedData can only be called by code whose caller-classloader |
| has been granted <q>read</q> permissions to the shared class cache.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>token</code> - a token to be used as a key</dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>ByteBuffer a read-only ByteBuffer containing the cached data, or null</dd> |
| </dl> |
| </li> |
| </ul> |
| <a id="storeSharedData(java.lang.String,java.nio.ByteBuffer)"> |
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| <h4>storeSharedData</h4> |
| <pre class="methodSignature"><a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/nio/ByteBuffer.html?is-external=true" title="class or interface in java.nio" class="externalLink" target="_blank">ByteBuffer</a> storeSharedData​(<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/String.html?is-external=true" title="class or interface in java.lang" class="externalLink" target="_blank">String</a> token, |
| <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/nio/ByteBuffer.html?is-external=true" title="class or interface in java.nio" class="externalLink" target="_blank">ByteBuffer</a> data)</pre> |
| <div class="block">Store data in the shared cache using a specific token.<p> |
| If the data is stored successfully, the shared read-only copy of the data is returned. Otherwise, null is returned.<br> |
| If data already exists for the token specified, the old data is marked <q>stale</q> in the cache and is replaced by the new data.<br> |
| If the exact same data already exists in the cache under the same token, the data is not duplicated and the cached version is returned.<br> |
| If null is passed as the data argument, the data currently stored against that token is marked <q>stale</q> and null is returned.<br> |
| If a SecurityManager is installed, storeSharedData can only be called by code whose caller-classloader |
| has been granted <q>write</q> permissions to the shared class cache.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>token</code> - a token to be used as a key</dd> |
| <dd><code>data</code> - a ByteBuffer of data to copy to the cache</dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>ByteBuffer a read-only ByteBuffer containing the cached data, or null</dd> |
| </dl> |
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