I've just discovered that one of our builds was hanging for 19 hours. Last line of build log is:

[FINDBUGS] Collecting findbugs analysis files...

Slave treads:

"Attach Listener" daemon prio=5 RUNNABLE

"Channel reader thread: channel" prio=5 RUNNABLE
java.net.SocketInputStream.socketRead0(Native Method)
java.net.SocketInputStream.read(Unknown Source)
java.net.SocketInputStream.read(Unknown Source)
java.io.FilterInputStream.read(Unknown Source)
java.io.BufferedInputStream.fill(Unknown Source)
java.io.BufferedInputStream.read(Unknown Source)
java.io.ObjectInputStream$PeekInputStream.peek(Unknown Source)
java.io.ObjectInputStream$BlockDataInputStream.peek(Unknown Source)
java.io.ObjectInputStream$BlockDataInputStream.peekByte(Unknown Source)
java.io.ObjectInputStream.readObject0(Unknown Source)
java.io.ObjectInputStream.readObject(Unknown Source)
hudson.remoting.Command.readFrom(Command.java:92)
hudson.remoting.ClassicCommandTransport.read(ClassicCommandTransport.java:59)
hudson.remoting.SynchronousCommandTransport$ReaderThread.run(SynchronousCommandTransport.java:48)

"Finalizer" daemon prio=8 WAITING
java.lang.Object.wait(Native Method)
java.lang.ref.ReferenceQueue.remove(Unknown Source)
java.lang.ref.ReferenceQueue.remove(Unknown Source)
java.lang.ref.Finalizer$FinalizerThread.run(Unknown Source)

"main" prio=5 WAITING
java.lang.Object.wait(Native Method)
java.lang.Object.wait(Object.java:503)
hudson.remoting.Channel.join(Channel.java:800)
hudson.remoting.Launcher.main(Launcher.java:484)
hudson.remoting.Launcher.runOnSocket(Launcher.java:375)
hudson.remoting.Launcher.runAsTcpServer(Launcher.java:365)
hudson.remoting.Launcher.run(Launcher.java:218)
hudson.remoting.Launcher.main(Launcher.java:180)

"Ping thread for channel hudson.remoting.Channel@bebb88:channel" daemon prio=5 TIMED_WAITING
java.lang.Thread.sleep(Native Method)
hudson.remoting.PingThread.run(PingThread.java:86)

"Ping thread for channel hudson.remoting.Channel@bebb88:channel" daemon prio=5 TIMED_WAITING
java.lang.Thread.sleep(Native Method)
hudson.remoting.PingThread.run(PingThread.java:86)

"Pipe writer thread: channel" prio=5 WAITING
sun.misc.Unsafe.park(Native Method)
java.util.concurrent.locks.LockSupport.park(Unknown Source)
java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
java.util.concurrent.LinkedBlockingQueue.take(Unknown Source)
java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
java.lang.Thread.run(Unknown Source)

"pool-1-svnkit-thread-1" daemon prio=5 WAITING
sun.misc.Unsafe.park(Native Method)
java.util.concurrent.locks.LockSupport.park(Unknown Source)
java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(Unknown Source)
java.util.concurrent.SynchronousQueue$TransferStack.transfer(Unknown Source)
java.util.concurrent.SynchronousQueue.take(Unknown Source)
java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
java.lang.Thread.run(Unknown Source)

"pool-1-svnkit-thread-2" daemon prio=5 WAITING
sun.misc.Unsafe.park(Native Method)
java.util.concurrent.locks.LockSupport.park(Unknown Source)
java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(Unknown Source)
java.util.concurrent.SynchronousQueue$TransferStack.transfer(Unknown Source)
java.util.concurrent.SynchronousQueue.take(Unknown Source)
java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
java.lang.Thread.run(Unknown Source)

"pool-1-thread-1965" prio=5 RUNNABLE
java.io.FileOutputStream.writeBytes(Native Method)
java.io.FileOutputStream.write(Unknown Source)
java.io.BufferedOutputStream.write(Unknown Source)
java.io.PrintStream.write(Unknown Source)
sun.nio.cs.StreamEncoder.writeBytes(Unknown Source)
sun.nio.cs.StreamEncoder.implFlushBuffer(Unknown Source)
sun.nio.cs.StreamEncoder.implFlush(Unknown Source)
sun.nio.cs.StreamEncoder.flush(Unknown Source)
java.io.OutputStreamWriter.flush(Unknown Source)
java.util.logging.StreamHandler.flush(Unknown Source)
java.util.logging.ConsoleHandler.publish(Unknown Source)
java.util.logging.Logger.log(Unknown Source)
java.util.logging.Logger.doLog(Unknown Source)
java.util.logging.Logger.log(Unknown Source)
java.util.logging.Logger.info(Unknown Source)
hudson.plugins.disk_usage.DiskUsageThread$DiskUsageCallable.getFileSize(DiskUsageThread.java:195)
hudson.plugins.disk_usage.DiskUsageThread$DiskUsageCallable.getFileSize(DiskUsageThread.java:192)
hudson.plugins.disk_usage.DiskUsageThread$DiskUsageCallable.getFileSize(DiskUsageThread.java:192)
hudson.plugins.disk_usage.DiskUsageThread$DiskUsageCallable.getFileSize(DiskUsageThread.java:192)
hudson.plugins.disk_usage.DiskUsageThread$DiskUsageCallable.getFileSize(DiskUsageThread.java:192)
hudson.plugins.disk_usage.DiskUsageThread$DiskUsageCallable.getFileSize(DiskUsageThread.java:192)
hudson.plugins.disk_usage.DiskUsageThread$DiskUsageCallable.getFileSize(DiskUsageThread.java:192)
hudson.plugins.disk_usage.DiskUsageThread$DiskUsageCallable.getFileSize(DiskUsageThread.java:192)
hudson.plugins.disk_usage.DiskUsageThread$DiskUsageCallable.getFileSize(DiskUsageThread.java:192)
hudson.plugins.disk_usage.DiskUsageThread$DiskUsageCallable.getFileSize(DiskUsageThread.java:192)
hudson.plugins.disk_usage.DiskUsageThread$DiskUsageCallable.getFileSize(DiskUsageThread.java:192)
hudson.plugins.disk_usage.DiskUsageThread$DiskUsageCallable.getFileSize(DiskUsageThread.java:192)
hudson.plugins.disk_usage.DiskUsageThread$DiskUsageCallable.call(DiskUsageThread.java:182)
hudson.plugins.disk_usage.DiskUsageThread$DiskUsageCallable.call(DiskUsageThread.java:169)
hudson.remoting.UserRequest.perform(UserRequest.java:118)
hudson.remoting.UserRequest.perform(UserRequest.java:48)
hudson.remoting.Request$2.run(Request.java:326)
hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
java.util.concurrent.FutureTask.run(Unknown Source)
java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
java.lang.Thread.run(Unknown Source)

"pool-1-thread-2080" prio=5 BLOCKED
java.util.logging.StreamHandler.publish(Unknown Source)
java.util.logging.ConsoleHandler.publish(Unknown Source)
java.util.logging.Logger.log(Unknown Source)
java.util.logging.Logger.doLog(Unknown Source)
java.util.logging.Logger.log(Unknown Source)
hudson.plugins.findbugs.parser.FindBugsParser.findSourceFile(FindBugsParser.java:322)
hudson.plugins.findbugs.parser.FindBugsParser.parse(FindBugsParser.java:238)
hudson.plugins.findbugs.parser.FindBugsParser.parse(FindBugsParser.java:145)
hudson.plugins.findbugs.parser.FindBugsParser.parse(FindBugsParser.java:105)
hudson.plugins.analysis.core.FilesParser.parseFile(FilesParser.java:306)
hudson.plugins.analysis.core.FilesParser.parseFiles(FilesParser.java:264)
hudson.plugins.analysis.core.FilesParser.parserCollectionOfFiles(FilesParser.java:215)
hudson.plugins.analysis.core.FilesParser.invoke(FilesParser.java:184)
hudson.plugins.analysis.core.FilesParser.invoke(FilesParser.java:31)
hudson.FilePath$FileCallableWrapper.call(FilePath.java:2387)
hudson.remoting.UserRequest.perform(UserRequest.java:118)
hudson.remoting.UserRequest.perform(UserRequest.java:48)
hudson.remoting.Request$2.run(Request.java:326)
hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
java.util.concurrent.FutureTask.run(Unknown Source)
java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
java.lang.Thread.run(Unknown Source)

"pool-1-thread-2202" prio=5 TIMED_WAITING
sun.misc.Unsafe.park(Native Method)
java.util.concurrent.locks.LockSupport.parkNanos(Unknown Source)
java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(Unknown Source)
java.util.concurrent.SynchronousQueue$TransferStack.transfer(Unknown Source)
java.util.concurrent.SynchronousQueue.poll(Unknown Source)
java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
java.lang.Thread.run(Unknown Source)

"pool-1-thread-2203" prio=5 RUNNABLE
java.lang.Thread.dumpThreads(Native Method)
java.lang.Thread.getAllStackTraces(Unknown Source)
net.bull.javamelody.JavaInformations.buildThreadInformationsList(JavaInformations.java:286)
net.bull.javamelody.JavaInformations.<init>(JavaInformations.java:187)
net.bull.javamelody.RemoteCallHelper$1.call(RemoteCallHelper.java:43)
net.bull.javamelody.RemoteCallHelper$1.call(RemoteCallHelper.java:35)
net.bull.javamelody.RemoteCallHelper$DelegatingTask.call(RemoteCallHelper.java:129)
hudson.remoting.UserRequest.perform(UserRequest.java:118)
hudson.remoting.UserRequest.perform(UserRequest.java:48)
hudson.remoting.Request$2.run(Request.java:326)
hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
java.util.concurrent.FutureTask.run(Unknown Source)
java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
java.lang.Thread.run(Unknown Source)

"Reference Handler" daemon prio=10 WAITING
java.lang.Object.wait(Native Method)
java.lang.Object.wait(Object.java:503)
java.lang.ref.Reference$ReferenceHandler.run(Unknown Source)