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https://issues.apache.org/jira/browse/SOLR-17060?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17786678#comment-17786678
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Andreas Hubold commented on SOLR-17060:
---------------------------------------
It seems this bug has been introduced with Solr 9. We have never seen it with
8.11.2 or earlier versions, and the metric "solr.<core>.segments", which
acquires a searcher here, was introduced with Solr 9 (part of SOLR-15428).
> CoreContainer#create may deadlock with concurrent requests for metrics
> ----------------------------------------------------------------------
>
> Key: SOLR-17060
> URL: https://issues.apache.org/jira/browse/SOLR-17060
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Components: multicore
> Affects Versions: 9.2.1
> Reporter: Andreas Hubold
> Priority: Major
> Labels: deadlock
>
> CoreContainer#create registers metrics for the created core quite early, and
> metrics can be requested for a core that is still being created. If a metrics
> request calls SolrCore#getSearcher with unlucky timing (race condition), then
> CoreContainer#create can deadlock.
> This problem was described on the users lists:
> [https://lists.apache.org/thread/mvpp1ogkxfdgfx87mdt6ylhqsttoq2dw]
> We ran into such a deadlock with Solr 9.2.1, a CoreAdmin CREATE request, and
> a periodic thread that requests all available JMX metrics.
> A CoreAdmin CREATE request was received, but its thread waits forever because
> onDeckSearchers is 1 and _searcher is null (variables checked in heap dump):
> {code:none}
> "qtp1800649922-28" #28 prio=5 os_prio=0 cpu=757.69ms elapsed=25383.63s
> tid=0x00007fe6dc9613a0 nid=0x70 in Object.wait() [0x00007fe6c68ca000]
> java.lang.Thread.State: WAITING (on object monitor)
> at java.lang.Object.wait(java.base@17.0.8.1/Native Method)
> - waiting on <no object reference available>
> at java.lang.Object.wait(java.base@17.0.8.1/Unknown Source)
> at org.apache.solr.core.SolrCore.getSearcher(SolrCore.java:2528)
> - locked <0x00000000e25dd2c8> (a java.lang.Object)
> at org.apache.solr.core.SolrCore.initSearcher(SolrCore.java:1283)
> at org.apache.solr.core.SolrCore.<init>(SolrCore.java:1168)
> at org.apache.solr.core.SolrCore.<init>(SolrCore.java:1051)
> at
> org.apache.solr.core.CoreContainer.createFromDescriptor(CoreContainer.java:1666)
> at org.apache.solr.core.CoreContainer.create(CoreContainer.java:1532)
> at
> org.apache.solr.handler.admin.CoreAdminOperation.lambda$static$0(CoreAdminOperation.java:111)
> at
> org.apache.solr.handler.admin.CoreAdminOperation$$Lambda$437/0x00007fe66048cc60.execute(Unknown
> Source)
> at
> org.apache.solr.handler.admin.CoreAdminOperation.execute(CoreAdminOperation.java:398)
> at
> org.apache.solr.handler.admin.CoreAdminHandler$CallInfo.call(CoreAdminHandler.java:354)
> at
> org.apache.solr.handler.admin.CoreAdminHandler.handleRequestBody(CoreAdminHandler.java:219)
> {code}
>
> There's no way for clients to retry the CREATE request, because CoreContainer
> rejects additional requests for good reason ("Already creating a core with
> name ...", see SOLR-14969).
> The only solution is to restart Solr.
>
> A thread for metrics was also waiting in the same way:
> {code:none}
> prometheus-http-1-1" #30 daemon prio=5 os_prio=0 cpu=1212.68ms
> elapsed=25383.60s tid=0x00007fe620008ac0 nid=0x73 in Object.wait()
> [0x00007fe6c680b000]
> java.lang.Thread.State: WAITING (on object monitor)
> at java.lang.Object.wait(java.base@17.0.8.1/Native Method)
> - waiting on <no object reference available>
> at java.lang.Object.wait(java.base@17.0.8.1/Unknown Source)
> at org.apache.solr.core.SolrCore.getSearcher(SolrCore.java:2528)
> - locked <0x00000000e25dd2c8> (a java.lang.Object)
> at org.apache.solr.core.SolrCore.getSearcher(SolrCore.java:2271)
> at org.apache.solr.core.SolrCore.getSearcher(SolrCore.java:2106)
> at org.apache.solr.core.SolrCore.withSearcher(SolrCore.java:2124)
> at org.apache.solr.core.SolrCore.getSegmentCount(SolrCore.java:534)
> at
> org.apache.solr.core.SolrCore.lambda$initializeMetrics$11(SolrCore.java:1360)
> at
> org.apache.solr.core.SolrCore$$Lambda$760/0x00007fe660634ec8.getValue(Unknown
> Source)
> at
> org.apache.solr.metrics.SolrMetricManager$GaugeWrapper.getValue(SolrMetricManager.java:779)
> at
> org.apache.solr.metrics.reporters.jmx.JmxMetricsReporter$JmxGauge.getValue(JmxMetricsReporter.java:207
> {code}
> This thread gathers multiple metrics one after the other. We can assume, that
> it had called SolrCore#getSearcher successfully before, and that the previous
> call has incremented onDeckSearchers to 1.
> A previous call to #getSearcher should eventually decrement onDeckSearchers
> again, and also set the _searcher field, but that's not happening. Normally,
> this should happen in SolrCore#registerSearcher, but that method is executed
> on the searcherExecutor, see
> [https://github.com/apache/solr/blob/releases/solr/9.2.1/solr/core/src/java/org/apache/solr/core/SolrCore.java#L2681]
> The problem is, that searcherExecutor will never execute #registerSearcher
> because the executor is still blocked by another job. This is because the
> core is still being created, see
> [https://github.com/apache/solr/blob/releases/solr/9.2.1/solr/core/src/java/org/apache/solr/core/SolrCore.java#L1160]
> {code:none}
> "searcherExecutor-14-thread-1-processing-studio" #50 prio=5 os_prio=0
> cpu=0.27ms elapsed=25212.18s tid=0x00007fe608146080 nid=0xbd waiting on
> condition [0x00007fe6c637a000]
> java.lang.Thread.State: WAITING (parking)
> at jdk.internal.misc.Unsafe.park(java.base@17.0.8.1/Native Method)
> - parking to wait for <0x00000000e738c1a8> (a
> java.util.concurrent.CountDownLatch$Sync)
> at
> java.util.concurrent.locks.LockSupport.park(java.base@17.0.8.1/Unknown
> Source)
> at
> java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(java.base@17.0.8.1/Unknown
> Source)
> at
> java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(java.base@17.0.8.1/Unknown
> Source)
> at
> java.util.concurrent.CountDownLatch.await(java.base@17.0.8.1/Unknown Source)
> at org.apache.solr.core.SolrCore.lambda$new$3(SolrCore.java:1162)
> at
> org.apache.solr.core.SolrCore$$Lambda$815/0x00007fe6606f3c40.call(Unknown
> Source)
> at java.util.concurrent.FutureTask.run(java.base@17.0.8.1/Unknown
> Source)
> {code}
> In summary, we have
> - thread "qtp1800649922-28" in SolrCore.<init> trying to create a core,
> which is waiting for
> - #registerSearcher job in the searcherExecutor work queue, which is waiting
> to be executed by
> - thread "searcherExecutor-14-thread-1-processing-studio" which waits for
> the first thread "qtp1800649922-28" to unblock it
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