title: Apache Ignite: "Blocked system-critical thread has been detected" exception in partition-exchanger
body: <p>I've got an Apache Ignite cluster made of 6 nodes. Occasionally, after a couple of hours of running, a number of the exceptions like below are recorded in the log and the node stops. I don't use event handlers or pub/sub handlers in the affected service. What could cause these exceptions? And does it means anything that the "partition-exchanger" thread is always mentioned in these error messages? </p>
  
  <pre><code> Jul 01, 2019 5:23:10 PM org.apache.ignite.logger.java.JavaLogger error
  SEVERE: Blocked system-critical thread has been detected. This can lead to cluster-wide undefined behaviour [threadName=partition-exchanger, blockedFor=61s]
  Jul 01, 2019 5:23:10 PM java.util.logging.LogManager$RootLogger log
  SEVERE: Critical system error detected. Will be handled accordingly to configured handler [hnd=StopNodeOrHaltFailureHandler [tryStop=false, timeout=0, super=AbstractFailureHandler [ignoredFailureTypes=[SYSTEM_WORKER_BLOCKED]]], failureCtx=FailureContext [type=SYSTEM_WORKER_BLOCKED, err=class o.a.i.IgniteException: GridWorker [name=partition-exchanger, igniteInstanceName=null, finished=false, heartbeatTs=1562001729657]]]
  class org.apache.ignite.IgniteException: GridWorker [name=partition-exchanger, igniteInstanceName=null, finished=false, heartbeatTs=1562001729657]
          at org.apache.ignite.internal.IgnitionEx$IgniteNamedInstance$2.apply(IgnitionEx.java:1831)
          at org.apache.ignite.internal.IgnitionEx$IgniteNamedInstance$2.apply(IgnitionEx.java:1826)
          at org.apache.ignite.internal.worker.WorkersRegistry.onIdle(WorkersRegistry.java:233)
          at org.apache.ignite.internal.util.worker.GridWorker.onIdle(GridWorker.java:297)
          at org.apache.ignite.spi.discovery.tcp.ServerImpl$RingMessageWorker.lambda$new$0(ServerImpl.java:2663)
          at org.apache.ignite.spi.discovery.tcp.ServerImpl$MessageWorker.body(ServerImpl.java:7181)
          at org.apache.ignite.spi.discovery.tcp.ServerImpl$RingMessageWorker.body(ServerImpl.java:2700)
          at org.apache.ignite.internal.util.worker.GridWorker.run(GridWorker.java:120)
          at org.apache.ignite.spi.discovery.tcp.ServerImpl$MessageWorkerThread.body(ServerImpl.java:7119)
          at org.apache.ignite.spi.IgniteSpiThread.run(IgniteSpiThread.java:62)
  </code></pre>
  
  <p>I use Apache Ignite for .Net v2.7 on a Linux container managed by Kubernetes. Thank you!</p>