buck daemon hangs trying to cleanup dir artifact cache

Created by: kageiit

After a buck command, the daemon hangs for a period of time before returning control of the shell back to the user. Yourkit says there is a potential deadlock

Potential deadlock: frozen threads found

It seems that the following threads have not changed their stack for more than 10 seconds.
These threads are possibly (but not necessarily!) in a deadlock or hung.

NGSession 1: com.facebook.buck.cli.Main (NGCommunicator reader) <--- Frozen for at least 21s
com.martiansoftware.nailgun.NGUnixDomainSocketLibrary.read(int, ByteBuffer, int) NGUnixDomainSocketLibrary.java (native)
com.martiansoftware.nailgun.NGUnixDomainSocket$NGUnixDomainSocketInputStream.doRead(ByteBuffer) NGUnixDomainSocket.java:125
com.martiansoftware.nailgun.NGUnixDomainSocket$NGUnixDomainSocketInputStream.read() NGUnixDomainSocket.java:98
java.io.DataInputStream.readInt() DataInputStream.java:387
com.martiansoftware.nailgun.NGCommunicator.readChunk() NGCommunicator.java:327
com.martiansoftware.nailgun.NGCommunicator.lambda$null$0() NGCommunicator.java:124
com.martiansoftware.nailgun.NGCommunicator$$Lambda$12.call()
java.util.concurrent.FutureTask.run() FutureTask.java:266
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor$Worker) ThreadPoolExecutor.java:1149
java.util.concurrent.ThreadPoolExecutor$Worker.run() ThreadPoolExecutor.java:624
java.lang.Thread.run() Thread.java:748

cc @msridhar @sbalabanov @styurin