PyroscopeAgent: stop method should stop/close Exporter as well

[REASY]

PyroscopeAgent: stop method should stop/close Exporter as well

Currently there is no way to stop daemon thread created in QueuedExporter.java. This is useful in case when one wants to have an app profiled dynamically without requiring restart. Imagine there is a long running app, I enable profiling for some amount of time, collect enough data and disable profiling. After some time I want to enable profiling again. Without stopping thread in QueuedExporter.java there will be many threads created and all waiting inside the loop in OverfillQueue.java

"Thread-174" - Thread t@742
   java.lang.Thread.State: WAITING
        at [email protected]/jdk.internal.misc.Unsafe.park(Native Method)
        - parking to wait for <778c4f25> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at [email protected]/java.util.concurrent.locks.LockSupport.park(LockSupport.java:341)
        at [email protected]/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:506)
        at [email protected]/java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3465)
        at [email protected]/java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3436)
        at [email protected]/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1623)
        at app//io.pyroscope.javaagent.OverfillQueue.take(OverfillQueue.java:63)
        at app//io.pyroscope.javaagent.impl.QueuedExporter.exportLoop(QueuedExporter.java:29)
        at app//io.pyroscope.javaagent.impl.QueuedExporter$$Lambda$1176/0x00007fa690e15470.run(Unknown Source)
        at [email protected]/java.lang.Thread.run(Thread.java:833)

   Locked ownable synchronizers:
        - None