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<h1 class="topictitle1">IBM Developer
Kit for Java advanced garbage collection</h1>
<div><p>The IBM<sup>®</sup> Developer
Kit for Java™ implements an advanced garbage collector algorithm.
This algorithm allows the discovery and collection of unreachable objects
without significant pauses in the operation of the Java program. A concurrent collector cooperatively
discovers the references to objects under the running threads, instead of
a single thread.</p>
<p>Many garbage collectors are "stop-the-world". This means that at the point
where a collection cycle occurs, all threads, except the thread that does
garbage collection, stop while the garbage collector does its work. When this
happens, Java programs experience a pause, and any multiple processor
capability of the platform is wasted relative to Java, while the collector does its work.
The iSeries™ algorithm
does not stop all program threads simultaneously. It allows those threads
to continue operation while the garbage collector completes its task. This
prevents the pauses, and allows all processors to be used during garbage collection.</p>
<p>Garbage collection occurs automatically based on parameters that you specify
when you start the Java virtual machine. Garbage collection
can also be started explicitly under the control of the Java program
by using the java.lang.Runtime.gc() method.</p>
<p>For a basic definition, see <a href="gc.htm">Java garbage
collection</a>.</p>
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<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="gc.htm" title="Garbage collection is the process of freeing storage that is used by objects that are no longer referred to by a program. With garbage collection, programmers no longer have to write error prone code to explicitly &#34;free&#34; or &#34;delete&#34; their objects. This code frequently results in &#34;memory leak&#34; program errors. The garbage collector automatically detects an object or group of objects that the user program can no longer reach. It does this because there are no references to that object in any program structure. Once the object has been collected, you can allocate the space for other uses.">Java garbage collection</a></div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
<div><a href="gcperf.htm" title="Garbage collection on the iSeries Java virtual machine operates in a continuous asynchronous mode. The garbage collection-initial size (GCHINL) parameter on the Run Java (RUNJVA) command may affect application performance.">Java garbage collection performance considerations</a></div>
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