ScheduledExecutorService && garbage collection

Сборщик удаляет объекты тогда, когда на них нет ссылок. Я сделал дамп кучи после вызова метода ExecutorService.shutdown(), но до выполнения запланированной задачи. Судя по нему, ссылок на экземпляр ScheduledExecutorService множество:

Rootset references to java.util.concurrent.ScheduledThreadPoolExecutor@0x6c1209178 (excludes weak refs)
References to java.util.concurrent.ScheduledThreadPoolExecutor@0x6c1209178 (112 bytes)
Java Local References
Java Local Reference (from java.lang.Thread@0x6c1208f88) :
--> java.util.concurrent.ScheduledThreadPoolExecutor@0x6c1209178 (112 bytes)
Java Local Reference (from java.lang.Thread@0x6c1208f88) :
--> java.util.concurrent.ThreadPoolExecutor$Worker@0x6c12091c8 (76 bytes) (field this$0:)
--> java.util.concurrent.ScheduledThreadPoolExecutor@0x6c1209178 (112 bytes) 
Java Local Reference (from java.lang.Thread@0x6c1208f88) :
--> java.lang.Thread@0x6c1208f88 (171 bytes) (field target:)
--> java.util.concurrent.ThreadPoolExecutor$Worker@0x6c12091c8 (76 bytes) (field this$0:)
--> java.util.concurrent.ScheduledThreadPoolExecutor@0x6c1209178 (112 bytes) 
Java Local Reference (from java.lang.Thread@0x6c1208f88) :
--> java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue@0x6c1209148 (52 bytes) (field queue:)
--> [Ljava.util.concurrent.RunnableScheduledFuture;@0x6c123e000 (144 bytes) (Element 0 of [Ljava.util.concurrent.RunnableScheduledFuture;@0x6c123e000:)
--> java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask@0x6c123e050 (96 bytes) (field this$0:)
--> java.util.concurrent.ScheduledThreadPoolExecutor@0x6c1209178 (112 bytes) 
Java Local Reference (from java.lang.Thread@0x6c1208f88) :
--> java.util.concurrent.locks.AbstractQueuedSynchronizer$Node@0x6c1209128 (52 bytes) (field thread:)
--> java.lang.Thread@0x6c1208f88 (171 bytes) (field target:)
--> java.util.concurrent.ThreadPoolExecutor$Worker@0x6c12091c8 (76 bytes) (field this$0:)
--> java.util.concurrent.ScheduledThreadPoolExecutor@0x6c1209178 (112 bytes) 
Java Local Reference (from java.lang.Thread@0x6c1208f88) :
--> java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject@0x6c1209110 (40 bytes) (field lastWaiter:)
--> java.util.concurrent.locks.AbstractQueuedSynchronizer$Node@0x6c1209128 (52 bytes) (field thread:)
--> java.lang.Thread@0x6c1208f88 (171 bytes) (field target:)
--> java.util.concurrent.ThreadPoolExecutor$Worker@0x6c12091c8 (76 bytes) (field this$0:)
--> java.util.concurrent.ScheduledThreadPoolExecutor@0x6c1209178 (112 bytes) 
Java Local Reference (from java.lang.ref.Reference$ReferenceHandler@0x6c1201de8) :
--> java.lang.ref.Reference$ReferenceHandler@0x6c1201de8 (171 bytes) (field group:)
--> java.lang.ThreadGroup@0x6c1201190 (67 bytes) (field groups:)
--> [Ljava.lang.ThreadGroup;@0x6c123dfc0 (48 bytes) (Element 0 of [Ljava.lang.ThreadGroup;@0x6c123dfc0:)
--> java.lang.ThreadGroup@0x6c1201160 (67 bytes) (field threads:)
--> [Ljava.lang.Thread;@0x6c123df30 (48 bytes) (Element 0 of [Ljava.lang.Thread;@0x6c123df30:)
--> java.lang.Thread@0x6c1208f88 (171 bytes) (field target:)
--> java.util.concurrent.ThreadPoolExecutor$Worker@0x6c12091c8 (76 bytes) (field this$0:)
--> java.util.concurrent.ScheduledThreadPoolExecutor@0x6c1209178 (112 bytes) 
Java Local Reference (from java.lang.ref.Finalizer$FinalizerThread@0x6c1201c28) :
--> java.lang.ref.Finalizer$FinalizerThread@0x6c1201c28 (172 bytes) (field group:)
--> java.lang.ThreadGroup@0x6c1201190 (67 bytes) (field groups:)
--> [Ljava.lang.ThreadGroup;@0x6c123dfc0 (48 bytes) (Element 0 of [Ljava.lang.ThreadGroup;@0x6c123dfc0:)
--> java.lang.ThreadGroup@0x6c1201160 (67 bytes) (field threads:)
--> [Ljava.lang.Thread;@0x6c123df30 (48 bytes) (Element 0 of [Ljava.lang.Thread;@0x6c123df30:)
--> java.lang.Thread@0x6c1208f88 (171 bytes) (field target:)
--> java.util.concurrent.ThreadPoolExecutor$Worker@0x6c12091c8 (76 bytes) (field this$0:)
--> java.util.concurrent.ScheduledThreadPoolExecutor@0x6c1209178 (112 bytes)

Трасса у всех разная, но с одним корнем в нативном вызове Unsafe.park()

Stack Trace for Java Local Reference
sun.misc.Unsafe.park((ZJ)V) : Unsafe.java line (native method)
java.util.concurrent.locks.LockSupport.parkNanos((Ljava/lang/Object;J)V) : LockSupport.java line 215
java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos((J)J) : AbstractQueuedSynchronizer.java line 2078
java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(()Ljava/util/concurrent/RunnableScheduledFuture;) : ScheduledThreadPoolExecutor.java line 1093
java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(()Ljava/lang/Object;) : ScheduledThreadPoolExecutor.java line 809
java.util.concurrent.ThreadPoolExecutor.getTask(()Ljava/lang/Runnable;) : ThreadPoolExecutor.java line 1074

Конкретно из этой трассы видно, что поток заснул на вызове ThreadPoolExecutor.getTask(), который удерживает кадр стека, в котором есть ссылка на экземпляр ScheduledExecutorService, что в свою очередь не даёт удалить его сборщику мусора.