title: Java ExecuterService deadlock?
body: <p>Recently I wrote some code to read JSON data from the web and update a MongoDB entry according to the data recieved. This has to be done for about 500,000 entries. To accelerate the process, I use a <code>ThreadPoolExecutor</code> with 5 threads and a blocking queue of size 50. Furthermore I use the <code>CallerRunsPolicy</code> for handling excess jobs.
  For every worker the job is as follows:</p>
  
  <ol>
  <li>Read JSON data from URL</li>
  <li>Parse JSON</li>
  <li>Update corresponding MongoDB entry</li>
  </ol>
  
  <p>However the programm gets stuck every time. Sometimes early, sometimes only after some hours. So far I haven't found any faults in the code. Exceptions are handled but not thrown and all methods used are supposed to be thread safe.</p>
  
  <p>Here is the thread dump after the programm hangs:</p>
  
  <pre><code>2016-01-16 23:40:05
  Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.66-b18 mixed mode):
  
  "JMX server connection timeout 711" #711 daemon prio=5 os_prio=0 tid=0x000000001813d000 nid=0x4e8 in Object.wait() [0x000000004733f000]
     java.lang.Thread.State: TIMED_WAITING (on object monitor)
      at java.lang.Object.wait(Native Method)
      at com.sun.jmx.remote.internal.ServerCommunicatorAdmin$Timeout.run(Unknown Source)
      - locked &lt;0x00000000e26162c8&gt; (a [I)
      at java.lang.Thread.run(Unknown Source)
  
     Locked ownable synchronizers:
      - None
  
  "RMI Scheduler(0)" #710 daemon prio=5 os_prio=0 tid=0x000000001813b800 nid=0x1ba0 waiting on condition [0x000000004723f000]
     java.lang.Thread.State: TIMED_WAITING (parking)
      at sun.misc.Unsafe.park(Native Method)
      - parking to wait for  &lt;0x00000000e1ce64e0&gt; (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
      at java.util.concurrent.locks.LockSupport.parkNanos(Unknown Source)
      at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(Unknown Source)
      at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(Unknown Source)
      at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
      at java.lang.Thread.run(Unknown Source)
  
     Locked ownable synchronizers:
      - None
  
  "RMI TCP Connection(1)-192.168.56.1" #709 daemon prio=5 os_prio=0 tid=0x0000000017714000 nid=0x11f0 runnable [0x000000004713e000]
     java.lang.Thread.State: RUNNABLE
      at java.net.SocketInputStream.socketRead0(Native Method)
      at java.net.SocketInputStream.socketRead(Unknown Source)
      at java.net.SocketInputStream.read(Unknown Source)
      at java.net.SocketInputStream.read(Unknown Source)
      at java.io.BufferedInputStream.fill(Unknown Source)
      at java.io.BufferedInputStream.read(Unknown Source)
      - locked &lt;0x00000000e25e5fe8&gt; (a java.io.BufferedInputStream)
      at java.io.FilterInputStream.read(Unknown Source)
      at sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown Source)
      at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown Source)
      at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$256(Unknown Source)
      at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler$$Lambda$1/917377658.run(Unknown Source)
      at java.security.AccessController.doPrivileged(Native Method)
      at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
      at java.lang.Thread.run(Unknown Source)
  
     Locked ownable synchronizers:
      - &lt;0x00000000e23ce048&gt; (a java.util.concurrent.ThreadPoolExecutor$Worker)
  
  "RMI TCP Accept-0" #708 daemon prio=5 os_prio=0 tid=0x0000000017fa2000 nid=0xd18 runnable [0x0000000046f3e000]
     java.lang.Thread.State: RUNNABLE
      at java.net.DualStackPlainSocketImpl.accept0(Native Method)
      at java.net.DualStackPlainSocketImpl.socketAccept(Unknown Source)
      at java.net.AbstractPlainSocketImpl.accept(Unknown Source)
      at java.net.PlainSocketImpl.accept(Unknown Source)
      - locked &lt;0x00000000e1ce8078&gt; (a java.net.SocksSocketImpl)
      at java.net.ServerSocket.implAccept(Unknown Source)
      at java.net.ServerSocket.accept(Unknown Source)
      at sun.management.jmxremote.LocalRMIServerSocketFactory$1.accept(Unknown Source)
      at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.executeAcceptLoop(Unknown Source)
      at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.run(Unknown Source)
      at java.lang.Thread.run(Unknown Source)
  
     Locked ownable synchronizers:
      - None
  
  "pool-1-thread-5" #19 prio=5 os_prio=0 tid=0x000000001859e000 nid=0x628 waiting on condition [0x0000000018f9e000]
     java.lang.Thread.State: WAITING (parking)
      at sun.misc.Unsafe.park(Native Method)
      - parking to wait for  &lt;0x00000000a57af940&gt; (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
      at java.util.concurrent.locks.LockSupport.park(Unknown Source)
      at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
      at java.util.concurrent.ArrayBlockingQueue.take(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
      at java.lang.Thread.run(Unknown Source)
  
     Locked ownable synchronizers:
      - None
  
  "pool-1-thread-4" #18 prio=5 os_prio=0 tid=0x000000001859d800 nid=0x2208 waiting on condition [0x0000000018e9f000]
     java.lang.Thread.State: WAITING (parking)
      at sun.misc.Unsafe.park(Native Method)
      - parking to wait for  &lt;0x00000000a57af940&gt; (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
      at java.util.concurrent.locks.LockSupport.park(Unknown Source)
      at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
      at java.util.concurrent.ArrayBlockingQueue.take(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
      at java.lang.Thread.run(Unknown Source)
  
     Locked ownable synchronizers:
      - None
  
  "pool-1-thread-3" #17 prio=5 os_prio=0 tid=0x000000001859c800 nid=0x239c waiting on condition [0x0000000018d9e000]
     java.lang.Thread.State: WAITING (parking)
      at sun.misc.Unsafe.park(Native Method)
      - parking to wait for  &lt;0x00000000a57af940&gt; (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
      at java.util.concurrent.locks.LockSupport.park(Unknown Source)
      at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
      at java.util.concurrent.ArrayBlockingQueue.take(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
      at java.lang.Thread.run(Unknown Source)
  
     Locked ownable synchronizers:
      - None
  
  "pool-1-thread-2" #16 prio=5 os_prio=0 tid=0x000000001859a000 nid=0x18a8 runnable [0x0000000018c9e000]
     java.lang.Thread.State: RUNNABLE
      at java.net.SocketInputStream.socketRead0(Native Method)
      at java.net.SocketInputStream.socketRead(Unknown Source)
      at java.net.SocketInputStream.read(Unknown Source)
      at java.net.SocketInputStream.read(Unknown Source)
      at java.io.BufferedInputStream.fill(Unknown Source)
      at java.io.BufferedInputStream.read1(Unknown Source)
      at java.io.BufferedInputStream.read(Unknown Source)
      - locked &lt;0x00000000f921a080&gt; (a java.io.BufferedInputStream)
      at sun.net.www.http.HttpClient.parseHTTPHeader(Unknown Source)
      at sun.net.www.http.HttpClient.parseHTTP(Unknown Source)
      at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(Unknown Source)
      - locked &lt;0x00000000f921a0c0&gt; (a sun.net.www.protocol.http.HttpURLConnection)
      at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
      - locked &lt;0x00000000f921a0c0&gt; (a sun.net.www.protocol.http.HttpURLConnection)
      at java.net.URL.openStream(Unknown Source)
      at Pr0grammDB.readURL(Pr0grammDB.java:217)
      at Pr0grammDB.readJSON(Pr0grammDB.java:210)
      at Pr0grammDB$1Job.run(Pr0grammDB.java:98)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
      at java.lang.Thread.run(Unknown Source)
  
     Locked ownable synchronizers:
      - &lt;0x00000000a57afa50&gt; (a java.util.concurrent.ThreadPoolExecutor$Worker)
  
  "pool-1-thread-1" #15 prio=5 os_prio=0 tid=0x0000000018599000 nid=0x20fc waiting on condition [0x0000000018b9f000]
     java.lang.Thread.State: WAITING (parking)
      at sun.misc.Unsafe.park(Native Method)
      - parking to wait for  &lt;0x00000000a57af940&gt; (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
      at java.util.concurrent.locks.LockSupport.park(Unknown Source)
      at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
      at java.util.concurrent.ArrayBlockingQueue.take(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
      at java.lang.Thread.run(Unknown Source)
  
     Locked ownable synchronizers:
      - None
  
  "pool-1-thread-1" #12 daemon prio=5 os_prio=0 tid=0x0000000017ecc800 nid=0x2bd8 waiting on condition [0x000000001879f000]
     java.lang.Thread.State: TIMED_WAITING (parking)
      at sun.misc.Unsafe.park(Native Method)
      - parking to wait for  &lt;0x00000000a57af298&gt; (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
      at java.util.concurrent.locks.LockSupport.parkNanos(Unknown Source)
      at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(Unknown Source)
      at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(Unknown Source)
      at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
      at java.lang.Thread.run(Unknown Source)
  
     Locked ownable synchronizers:
      - None
  
  "cluster-ClusterId{value='569a6466a802c513644d5a51', description='null'}-127.0.0.1:27017" #11 daemon prio=5 os_prio=0 tid=0x000000001785e000 nid=0x1de8 waiting on condition [0x000000001869e000]
     java.lang.Thread.State: TIMED_WAITING (parking)
      at sun.misc.Unsafe.park(Native Method)
      - parking to wait for  &lt;0x00000000a57ad528&gt; (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
      at java.util.concurrent.locks.LockSupport.parkNanos(Unknown Source)
      at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(Unknown Source)
      at com.mongodb.connection.DefaultServerMonitor$ServerMonitorRunnable.waitForSignalOrTimeout(DefaultServerMonitor.java:237)
      at com.mongodb.connection.DefaultServerMonitor$ServerMonitorRunnable.waitForNext(DefaultServerMonitor.java:218)
      at com.mongodb.connection.DefaultServerMonitor$ServerMonitorRunnable.run(DefaultServerMonitor.java:167)
      - locked &lt;0x00000000a57ad270&gt; (a com.mongodb.connection.DefaultServerMonitor$ServerMonitorRunnable)
      at java.lang.Thread.run(Unknown Source)
  
     Locked ownable synchronizers:
      - None
  
  "Service Thread" #9 daemon prio=9 os_prio=0 tid=0x0000000017493800 nid=0x23a8 runnable [0x0000000000000000]
     java.lang.Thread.State: RUNNABLE
  
     Locked ownable synchronizers:
      - None
  
  "C1 CompilerThread2" #8 daemon prio=9 os_prio=2 tid=0x0000000015af8800 nid=0x2f5c waiting on condition [0x0000000000000000]
     java.lang.Thread.State: RUNNABLE
  
     Locked ownable synchronizers:
      - None
  
  "C2 CompilerThread1" #7 daemon prio=9 os_prio=2 tid=0x0000000015af1800 nid=0x18c0 waiting on condition [0x0000000000000000]
     java.lang.Thread.State: RUNNABLE
  
     Locked ownable synchronizers:
      - None
  
  "C2 CompilerThread0" #6 daemon prio=9 os_prio=2 tid=0x0000000015aef000 nid=0x15f8 waiting on condition [0x0000000000000000]
     java.lang.Thread.State: RUNNABLE
  
     Locked ownable synchronizers:
      - None
  
  "Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x0000000015aec800 nid=0x2074 waiting on condition [0x0000000000000000]
     java.lang.Thread.State: RUNNABLE
  
     Locked ownable synchronizers:
      - None
  
  "Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x0000000015aec000 nid=0x2c94 runnable [0x0000000000000000]
     java.lang.Thread.State: RUNNABLE
  
     Locked ownable synchronizers:
      - None
  
  "Finalizer" #3 daemon prio=8 os_prio=1 tid=0x00000000022b8000 nid=0x2f14 in Object.wait() [0x0000000016e4f000]
     java.lang.Thread.State: WAITING (on object monitor)
      at java.lang.Object.wait(Native Method)
      - waiting on &lt;0x00000000a57ebd08&gt; (a java.lang.ref.ReferenceQueue$Lock)
      at java.lang.ref.ReferenceQueue.remove(Unknown Source)
      - locked &lt;0x00000000a57ebd08&gt; (a java.lang.ref.ReferenceQueue$Lock)
      at java.lang.ref.ReferenceQueue.remove(Unknown Source)
      at java.lang.ref.Finalizer$FinalizerThread.run(Unknown Source)
  
     Locked ownable synchronizers:
      - None
  
  "Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x00000000022af000 nid=0x83c in Object.wait() [0x0000000016d4f000]
     java.lang.Thread.State: WAITING (on object monitor)
      at java.lang.Object.wait(Native Method)
      - waiting on &lt;0x00000000a57ebf20&gt; (a java.lang.ref.Reference$Lock)
      at java.lang.Object.wait(Unknown Source)
      at java.lang.ref.Reference$ReferenceHandler.run(Unknown Source)
      - locked &lt;0x00000000a57ebf20&gt; (a java.lang.ref.Reference$Lock)
  
     Locked ownable synchronizers:
      - None
  
  "main" #1 prio=5 os_prio=0 tid=0x000000000207e000 nid=0x1964 runnable [0x000000000217e000]
     java.lang.Thread.State: RUNNABLE
      at java.net.SocketInputStream.socketRead0(Native Method)
      at java.net.SocketInputStream.socketRead(Unknown Source)
      at java.net.SocketInputStream.read(Unknown Source)
      at java.net.SocketInputStream.read(Unknown Source)
      at java.io.BufferedInputStream.fill(Unknown Source)
      at java.io.BufferedInputStream.read1(Unknown Source)
      at java.io.BufferedInputStream.read(Unknown Source)
      - locked &lt;0x00000000f921c318&gt; (a java.io.BufferedInputStream)
      at sun.net.www.http.HttpClient.parseHTTPHeader(Unknown Source)
      at sun.net.www.http.HttpClient.parseHTTP(Unknown Source)
      at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(Unknown Source)
      - locked &lt;0x00000000f921c358&gt; (a sun.net.www.protocol.http.HttpURLConnection)
      at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
      - locked &lt;0x00000000f921c358&gt; (a sun.net.www.protocol.http.HttpURLConnection)
      at java.net.URL.openStream(Unknown Source)
      at Pr0grammDB.readURL(Pr0grammDB.java:217)
      at Pr0grammDB.readJSON(Pr0grammDB.java:210)
      at Pr0grammDB$1Job.run(Pr0grammDB.java:98)
      at java.util.concurrent.ThreadPoolExecutor$CallerRunsPolicy.rejectedExecution(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor.reject(Unknown Source)
      at java.util.concurrent.ThreadPoolExecutor.execute(Unknown Source)
      at Pr0grammDB.addAdditionalData(Pr0grammDB.java:114)
      at Pr0grammDB.main(Pr0grammDB.java:48)
  
     Locked ownable synchronizers:
      - None
  
  "VM Thread" os_prio=2 tid=0x0000000015ab7000 nid=0x684 runnable 
  
  "GC task thread#0 (ParallelGC)" os_prio=0 tid=0x00000000021d7800 nid=0x28e0 runnable 
  
  "GC task thread#1 (ParallelGC)" os_prio=0 tid=0x00000000021d9000 nid=0x2658 runnable 
  
  "GC task thread#2 (ParallelGC)" os_prio=0 tid=0x00000000021da800 nid=0x273c runnable 
  
  "GC task thread#3 (ParallelGC)" os_prio=0 tid=0x00000000021dd000 nid=0x20f8 runnable 
  
  "VM Periodic Task Thread" os_prio=2 tid=0x00000000174a2000 nid=0x824 waiting on condition 
  
  JNI global references: 385
  </code></pre>
  
  <p>All threads except for one seem to be waiting. However I don't know what they are waiting for. The other one seems to be stuck in socketRead.</p>
  
  <p>When the code hangs the heap usage is somewhat weird, too. It ascends to about 400MB before dropping to 100MB and repeating. One cycle taking about 1h.</p>
  
  <p>Maybe you can help me find the problem?</p>