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| <title>Analyzing Finalizer</title> |
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| <h1 class="title topictitle1" id="ariaid-title1">Analyzing Finalizer</h1> |
| |
| |
| |
| <div class="body taskbody"> |
| <div class="section context"> |
| <p class="p"> Finalizers are executed when the internal garbage collection |
| cleans up the objects. Since you have no control over the finalizer |
| execution, it is recommended not to use them. Because the memory can |
| only be released when the finalize method finished, long running |
| tasks in the finalizer can block the garbage collection. To get the |
| finalizers overview select Finalizer Overview Query from the query |
| list:</p> |
| |
| <img class="image" src="../mimes/finalizers.png" alt="Finalizer overview menu option and report" /> |
| <p class="p">This query includes the following subqueries:</p> |
| |
| |
| <div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" class="table" frame="border" border="1" rules="all"><colgroup><col /><col /></colgroup><tbody class="tbody"> |
| <tr id="task_analyzingfinalizer__finalizer_in_processing" class="row"> |
| <td class="entry cellrowborder" style="vertical-align:top;"> |
| <strong class="ph b">Finalizer in Processing</strong> |
| </td> |
| |
| <td class="entry cellrowborder" style="vertical-align:top;"> |
| <p class="p"> Extract the object currently processed by Finalizer Thread. This |
| query returns the currently processed object by the Finalizer |
| Thread if any. The returned object can be processed for one of |
| the following reasons:</p> |
| |
| <ul class="ul"> |
| <li class="li">it is blocking</li> |
| |
| <li class="li">it is long running</li> |
| |
| <li class="li">the finalizer queue was or is still full.</li> |
| |
| </ul> |
| |
| <p class="p"> Use the finalizer queue query to check the queue.</p> |
| |
| </td> |
| |
| </tr> |
| |
| <tr id="task_analyzingfinalizer__ready_for_finalizer_thread" class="row"> |
| <td class="entry cellrowborder" style="vertical-align:top;"> |
| <strong class="ph b">Ready for Finalizer Thread</strong> |
| </td> |
| |
| <td class="entry cellrowborder" style="vertical-align:top;"> |
| <p class="p"> This query shows the objects ready for finalization in their |
| processing order. Following reasons can cause a full finalizer |
| queue:</p> |
| |
| <ul class="ul"> |
| <li class="li"> The currently processed object is blocking or long running |
| (please use our finalizer in processing query to check).</li> |
| |
| <li class="li"> The application made use of too many objects with |
| finalize() which are queued up in memory.</li> |
| |
| </ul> |
| |
| <div class="note"><span class="notetitle">Note:</span> |
| On J9 JVM-based dumps (e.g. IBM Java, OpenJ9), as expected, this |
| list shows objects waiting to be finalized. On previous versions |
| of Memory Analyzer (1.10 and earlier) it also showed those |
| which have already been finalized and are waiting to be |
| garbage collected. Those objects where finalization has been |
| completed are not now shown by this query, but might be in |
| the unreachable objects histogram if they are waiting to be |
| reclaimed. |
| <p class="p">States</p> |
| |
| <ol class="ol"> |
| <li class="li">Initially objects with a finalize method start in the |
| <a class="xref" href="../concepts/gcroots.html">UNFINALIZED</a> state. |
| With a J9 heap dump this is visible as an inbound <code class="ph codeph"><Unfinalized></code> reference from |
| the <code class="ph codeph">java.lang.Runtime</code> object.</li> |
| |
| <li class="li">Once the object is no longer <a class="xref" href="../concepts/reachability.html">reachable</a> |
| it goes onto the finalizer queue, visible via this query and with |
| J9 heap dumps as a <a class="xref" href="../concepts/gcroots.html">FINALIZABLE GC root</a>.</li> |
| |
| <li class="li">Once finalization is completed the object is not seen in either of these two |
| ways. Normally it would be garbage collected, but if the <code class="ph codeph">finalizer()</code> |
| code made the object reachable again by storing a reference to it in an ordinary object |
| it might still be strongly reachable.</li> |
| |
| </ol> |
| |
| </div> |
| |
| <p class="p"> Additionally a class-level summary of the objects is provided</p> |
| |
| </td> |
| |
| </tr> |
| |
| <tr id="task_analyzingfinalizer__finalizer_thread" class="row"> |
| <td class="entry cellrowborder" style="vertical-align:top;"> |
| <strong class="ph b">Finalizer Thread</strong> |
| </td> |
| |
| <td class="entry cellrowborder" style="vertical-align:top;"> This query shows the daemon thread which performs the |
| object finalizations.</td> |
| |
| </tr> |
| |
| <tr id="task_analyzingfinalizer__finalizer_thread_locals" class="row"> |
| <td class="entry cellrowborder" style="vertical-align:top;"> |
| <strong class="ph b">Finalizer Thread Locals</strong> |
| </td> |
| |
| <td class="entry cellrowborder" style="vertical-align:top;"> |
| <p class="p"> |
| This query shows the thread locals of the daemon thread that |
| performs the object finalizations. If there are any, this |
| indicates misuse in at least one of the processed finalizers |
| ( |
| <span class="keyword cmdname">finalize()</span> |
| implemented wrong) and might cause severe problems (e.g. |
| unreclaimed memory permanently hold by the finalizer thread or |
| finalizer processed under useless thread locals harming |
| application logic) |
| </p> |
| |
| </td> |
| |
| </tr> |
| |
| </tbody> |
| </table> |
| </div> |
| |
| <p class="p">The <a class="xref" href="../reference/inspections/component_report.html#ref_inspections_component_report__finalizer">component report</a> also includes information about objects |
| belonging to the component which implement the <code class="ph codeph">finalize()</code> method |
| and so could be finalized at some point.</p> |
| |
| </div> |
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