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<div class="sub-title"><span class="module-label-in-type">Module</span>&nbsp;<a href="../../../../module-summary.html">openj9.sharedclasses</a></div>
<div class="sub-title"><span class="package-label-in-type">Package</span>&nbsp;<a href="package-summary.html">com.ibm.oti.shared</a></div>
<h1 title="Interface SharedDataHelper" class="title">Interface SharedDataHelper</h1>
</div>
<section class="class-description" id="class-description">
<dl class="notes">
<dt>All Superinterfaces:</dt>
<dd><code><a href="SharedHelper.html" title="interface in com.ibm.oti.shared">SharedHelper</a></code></dd>
</dl>
<hr>
<div class="type-signature"><span class="modifiers">public interface </span><span class="element-name type-name-label">SharedDataHelper</span><span class="extends-implements">
extends <a href="SharedHelper.html" title="interface in com.ibm.oti.shared">SharedHelper</a></span></div>
<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Since the shared cache is persistent beyond the lifetime of a JVM, data in the shared cache may become out-of-date (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 class="notes">
<dt>See Also:</dt>
<dd>
<ul class="see-list">
<li><a href="SharedHelper.html" title="interface in com.ibm.oti.shared"><code>SharedHelper</code></a></li>
<li><a href="SharedDataHelperFactory.html" title="interface in com.ibm.oti.shared"><code>SharedDataHelperFactory</code></a></li>
<li><a href="SharedClassPermission.html" title="class in com.ibm.oti.shared"><code>SharedClassPermission</code></a></li>
</ul>
</dd>
</dl>
</section>
<section class="summary">
<ul class="summary-list">
<!-- ========== METHOD SUMMARY =========== -->
<li>
<section class="method-summary" id="method-summary">
<h2>Method Summary</h2>
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<div class="table-tabs" role="tablist" aria-orientation="horizontal"><button id="method-summary-table-tab0" role="tab" aria-selected="true" aria-controls="method-summary-table.tabpanel" tabindex="0" onkeydown="switchTab(event)" onclick="show('method-summary-table', 'method-summary-table', 3)" class="active-table-tab">All Methods</button><button id="method-summary-table-tab2" role="tab" aria-selected="false" aria-controls="method-summary-table.tabpanel" tabindex="-1" onkeydown="switchTab(event)" onclick="show('method-summary-table', 'method-summary-table-tab2', 3)" class="table-tab">Instance Methods</button><button id="method-summary-table-tab3" role="tab" aria-selected="false" aria-controls="method-summary-table.tabpanel" tabindex="-1" onkeydown="switchTab(event)" onclick="show('method-summary-table', 'method-summary-table-tab3', 3)" class="table-tab">Abstract Methods</button></div>
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<div class="summary-table three-column-summary" aria-labelledby="method-summary-table-tab0">
<div class="table-header col-first">Modifier and Type</div>
<div class="table-header col-second">Method</div>
<div class="table-header col-last">Description</div>
<div class="col-first even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="https://docs.oracle.com/en/java/javase/18/docs/api/java.base/java/nio/ByteBuffer.html" title="class or interface in java.nio" class="external-link" target="_blank">ByteBuffer</a></code></div>
<div class="col-second even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="#findSharedData(java.lang.String)" class="member-name-link">findSharedData</a><wbr>(<a href="https://docs.oracle.com/en/java/javase/18/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link" target="_blank">String</a>&nbsp;token)</code></div>
<div class="col-last even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3">
<div class="block">Find data in the shared cache using a specific token.</div>
</div>
<div class="col-first odd-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="https://docs.oracle.com/en/java/javase/18/docs/api/java.base/java/nio/ByteBuffer.html" title="class or interface in java.nio" class="external-link" target="_blank">ByteBuffer</a></code></div>
<div class="col-second odd-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="#storeSharedData(java.lang.String,java.nio.ByteBuffer)" class="member-name-link">storeSharedData</a><wbr>(<a href="https://docs.oracle.com/en/java/javase/18/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link" target="_blank">String</a>&nbsp;token,
<a href="https://docs.oracle.com/en/java/javase/18/docs/api/java.base/java/nio/ByteBuffer.html" title="class or interface in java.nio" class="external-link" target="_blank">ByteBuffer</a>&nbsp;data)</code></div>
<div class="col-last odd-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3">
<div class="block">Store data in the shared cache using a specific token.</div>
</div>
</div>
</div>
</div>
<div class="inherited-list">
<h3 id="methods-inherited-from-class-com.ibm.oti.shared.SharedHelper">Methods declared in interface&nbsp;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></div>
</section>
</li>
</ul>
</section>
<section class="details">
<ul class="details-list">
<!-- ============ METHOD DETAIL ========== -->
<li>
<section class="method-details" id="method-detail">
<h2>Method Details</h2>
<ul class="member-list">
<li>
<section class="detail" id="findSharedData(java.lang.String)">
<h3>findSharedData</h3>
<div class="member-signature"><span class="return-type"><a href="https://docs.oracle.com/en/java/javase/18/docs/api/java.base/java/nio/ByteBuffer.html" title="class or interface in java.nio" class="external-link" target="_blank">ByteBuffer</a></span>&nbsp;<span class="element-name">findSharedData</span><wbr><span class="parameters">(<a href="https://docs.oracle.com/en/java/javase/18/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link" target="_blank">String</a>&nbsp;token)</span></div>
<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 class="notes">
<dt>Parameters:</dt>
<dd><code>token</code> - a token to be used as a key</dd>
<dt>Returns:</dt>
<dd>ByteBuffer a read-only ByteBuffer containing the cached data, or null</dd>
</dl>
</section>
</li>
<li>
<section class="detail" id="storeSharedData(java.lang.String,java.nio.ByteBuffer)">
<h3>storeSharedData</h3>
<div class="member-signature"><span class="return-type"><a href="https://docs.oracle.com/en/java/javase/18/docs/api/java.base/java/nio/ByteBuffer.html" title="class or interface in java.nio" class="external-link" target="_blank">ByteBuffer</a></span>&nbsp;<span class="element-name">storeSharedData</span><wbr><span class="parameters">(<a href="https://docs.oracle.com/en/java/javase/18/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link" target="_blank">String</a>&nbsp;token,
<a href="https://docs.oracle.com/en/java/javase/18/docs/api/java.base/java/nio/ByteBuffer.html" title="class or interface in java.nio" class="external-link" target="_blank">ByteBuffer</a>&nbsp;data)</span></div>
<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 class="notes">
<dt>Parameters:</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>Returns:</dt>
<dd>ByteBuffer a read-only ByteBuffer containing the cached data, or null</dd>
</dl>
</section>
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