Scala Console App Does Not Exit When Using Reactive Mongo Driver - mongodb

Question

I am using ReactiveMongo 0.16.1 and MongoDB 4.0.
In the Main class I run the following:
DataManager.processFeedbacks
val future1 = DataManager.processNewEvaluations
val future2 = DataManager.processPurchases
val future3 = DataManager.processExpiredEvaluations
val future4 = DataManager.processExpiredCommerialLicenses
val futures = List(future1, future2, future3, future4).map(_.map(Try(_)))
val complete = Future.sequence(futures).onComplete _
complete(_ => {
DatabaseConfigService.closeDriver
})
All works fine except that I cannot close the driver and the main thread continues to hang not allowing the app to exit.
In closeDriver(), I tried driver.close, conn.askClose()(Duration.create(10, TimeUnit.SECONDS), and
futureConnection.map(conn => {
conn.askClose()(Duration.create(10, TimeUnit.SECONDS))
.onComplete(y => driver.close())
})
And all without a result, as you could guess.
Here is the dump threads:
2019-02-05 14:33:18
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.191-b12 mixed mode):
"Analytics" #68 prio=1 os_prio=31 tid=0x00007fc9fd92c800 nid=0x9f07 waiting on condition [0x000070000dc97000]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x000000076b960148> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at com.segment.analytics.Platform$1$1.run(Platform.java:45)
at java.lang.Thread.run(Thread.java:748)
"DestroyJavaVM" #40 prio=5 os_prio=31 tid=0x00007fc9fc0ff000 nid=0x1903 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Analytics" #32 prio=1 os_prio=31 tid=0x00007fc9fe0b4800 nid=0x6203 waiting on condition [0x000070000eecd000]
java.lang.Thread.State: TIMED_WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x000000076ba51808> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1093)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at com.segment.analytics.Platform$1$1.run(Platform.java:45)
at java.lang.Thread.run(Thread.java:748)
"Analytics" #31 prio=1 os_prio=31 tid=0x00007fc9fe0b2800 nid=0x6103 waiting on condition [0x000070000edca000]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x000000076ba3a870> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
at com.segment.analytics.internal.AnalyticsClient$Looper.run(AnalyticsClient.java:106)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at com.segment.analytics.Platform$1$1.run(Platform.java:45)
at java.lang.Thread.run(Thread.java:748)
"Service Thread" #10 daemon prio=9 os_prio=31 tid=0x00007fc9fe0dd000 nid=0x3e03 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C1 CompilerThread3" #9 daemon prio=9 os_prio=31 tid=0x00007fc9ff00b800 nid=0x4003 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread2" #8 daemon prio=9 os_prio=31 tid=0x00007fc9fc801000 nid=0x3c03 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread1" #7 daemon prio=9 os_prio=31 tid=0x00007fc9fc1b1800 nid=0x3b03 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread0" #6 daemon prio=9 os_prio=31 tid=0x00007fc9fe0dc800 nid=0x3903 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Monitor Ctrl-Break" #5 daemon prio=5 os_prio=31 tid=0x00007fc9fe0db000 nid=0x3703 runnable [0x000070000d582000]
java.lang.Thread.State: RUNNABLE
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
at java.net.SocketInputStream.read(SocketInputStream.java:171)
at java.net.SocketInputStream.read(SocketInputStream.java:141)
at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
- locked <0x00000006c0015800> (a java.io.InputStreamReader)
at java.io.InputStreamReader.read(InputStreamReader.java:184)
at java.io.BufferedReader.fill(BufferedReader.java:161)
at java.io.BufferedReader.readLine(BufferedReader.java:324)
- locked <0x00000006c0015800> (a java.io.InputStreamReader)
at java.io.BufferedReader.readLine(BufferedReader.java:389)
at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:64)
"Signal Dispatcher" #4 daemon prio=9 os_prio=31 tid=0x00007fc9fb85d000 nid=0x4303 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Finalizer" #3 daemon prio=8 os_prio=31 tid=0x00007fc9fd800000 nid=0x4703 in Object.wait() [0x000070000d37c000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x00000006c00170e0> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
- locked <0x00000006c00170e0> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)
"Reference Handler" #2 daemon prio=10 os_prio=31 tid=0x00007fc9fb83f800 nid=0x4903 in Object.wait() [0x000070000d279000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x00000006c001e220> (a java.lang.ref.Reference$Lock)
at java.lang.Object.wait(Object.java:502)
at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
- locked <0x00000006c001e220> (a java.lang.ref.Reference$Lock)
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)
"VM Thread" os_prio=31 tid=0x00007fc9fb839000 nid=0x4b03 runnable
"GC task thread#0 (ParallelGC)" os_prio=31 tid=0x00007fc9fe801800 nid=0x2507 runnable
"GC task thread#1 (ParallelGC)" os_prio=31 tid=0x00007fc9fe802800 nid=0x2a03 runnable
"GC task thread#2 (ParallelGC)" os_prio=31 tid=0x00007fc9fe803000 nid=0x2b03 runnable
"GC task thread#3 (ParallelGC)" os_prio=31 tid=0x00007fc9ff000000 nid=0x5203 runnable
"GC task thread#4 (ParallelGC)" os_prio=31 tid=0x00007fc9ff001000 nid=0x5003 runnable
"GC task thread#5 (ParallelGC)" os_prio=31 tid=0x00007fc9ff800000 nid=0x4f03 runnable
"GC task thread#6 (ParallelGC)" os_prio=31 tid=0x00007fc9fe00a000 nid=0x2d03 runnable
"GC task thread#7 (ParallelGC)" os_prio=31 tid=0x00007fc9ff801000 nid=0x2e03 runnable
"VM Periodic Task Thread" os_prio=31 tid=0x00007fc9fe800000 nid=0x5503 waiting on condition
JNI global references: 2012
Heap
PSYoungGen total 116736K, used 58485K [0x000000076ab00000, 0x0000000772a80000, 0x00000007c0000000)
eden space 105984K, 55% used [0x000000076ab00000,0x000000076e41d548,0x0000000771280000)
from space 10752K, 0% used [0x0000000771d00000,0x0000000771d00000,0x0000000772780000)
to space 10752K, 0% used [0x0000000771280000,0x0000000771280000,0x0000000771d00000)
ParOldGen total 141312K, used 10517K [0x00000006c0000000, 0x00000006c8a00000, 0x000000076ab00000)
object space 141312K, 7% used [0x00000006c0000000,0x00000006c0a45578,0x00000006c8a00000)
Metaspace used 38906K, capacity 42786K, committed 42968K, reserved 1087488K
class space used 5527K, capacity 5819K, committed 5888K, reserved 1048576K
P.S. It seems that I have the same problem as described here. However, that post was from 2015 and a fix should have been deployed a long time ago... Nevertheless, I still cannot close the driver.

Answer 1

As it often happens, the problem was between the computer and the chair... I post the answer here, in the hope that it maybe help someone one day.
I missed that the very first line in the code DataManager.processFeedbacks also creates a future. I was not waiting for its completion and was closing the driver too early.
I figured it out by checking the dump threads again and looking for the classes that my code was using. One of the classes was used by the processFeedbacks() function