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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 edited comment on SOLR-17060 at 11/16/23 9:04 AM:
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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>.INDEX.segments", which 
acquires a searcher here, was introduced with Solr 9 (part of SOLR-15428).


was (Author: ahubold):
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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