ssh.rb

require 'java'
require 'jsch-0.1.38.jar'

class SSH
  include_package "com.jcraft.jsch"

  def initialize(host, username, password)
    @client = JSch.new
    @session = @client.getSession(username, host, 22)
    @session.setPassword(password)
    @session.setConfig("StrictHostKeyChecking", "no")
    @session.connect(5000)

    @channels = []
  end

  def execute_command(command)
    channel, input = channel_input_for_command(command)
    channel.connect
    @channels << channel
    tmp = ('0'*1024).to_java_bytes
    result = ''

    until channel.isClosed
      while input.available > 0
        i = input.read(tmp, 0, 1024)
        break if i < 0
        result << java.lang.String.new(tmp, 0, i).to_s
      end
    end

    result
  end

  def tail(files, &block)
    channel, input = channel_input_for_command("tail -F -n 1 #{files}")
    channel.setPty(true)
    @channels << channel
    channel.connect
    tmp = ('0'*1024).to_java_bytes

    string = ''
    until channel.isClosed
      while input.available > 0
        i = input.read(tmp, 0, 1024)
        break if i < 0
        string << java.lang.String.new(tmp, 0, i).to_s
      end

      unless string.empty?
        yield string
        string = ''
      end
    end
  end

  def close
    @channels.each { |c| c.disconnect }
    @session.disconnect
    true
  end

  private

  def channel_input_for_command(command)
    channel = @session.openChannel("exec")
    channel.setCommand(command)
    channel.setInputStream(nil)
    [channel, channel.getInputStream]
  end

end

at_exit { puts "main thread exiting" }
ssh = SSH.new('localhost', 'jarib', 'foo')
puts ssh.execute_command("ls")

# prints "main thread exiting", then just hangs
# if ssh.close is called, it exits fine

thread_dump.txt

Full thread dump Java HotSpot(TM) 64-Bit Server VM (1.6.0_05-b13-52 mixed mode):

"DestroyJavaVM" prio=5 tid=0x0000000101801000 nid=0x100401000 waiting on condition [0x0000000000000000..0x0000000100400aa0]
   java.lang.Thread.State: RUNNABLE

"Connect thread localhost session" prio=5 tid=0x000000010197c800 nid=0x12aafa000 runnable [0x000000012aaf9000..0x000000012aaf9ad0]
   java.lang.Thread.State: RUNNABLE
	at java.net.SocketInputStream.socketRead0(Native Method)
	at java.net.SocketInputStream.read(SocketInputStream.java:129)
	at com.jcraft.jsch.IO.getByte(IO.java:82)
	at com.jcraft.jsch.Session.read(Session.java:795)
	at com.jcraft.jsch.Session.run(Session.java:1160)
	at java.lang.Thread.run(Thread.java:637)

"Low Memory Detector" daemon prio=5 tid=0x0000000101844800 nid=0x12a0f7000 runnable [0x0000000000000000..0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"CompilerThread1" daemon prio=9 tid=0x0000000101843000 nid=0x129ff4000 waiting on condition [0x0000000000000000..0x0000000129ff23e0]
   java.lang.Thread.State: RUNNABLE

"CompilerThread0" daemon prio=9 tid=0x0000000101841800 nid=0x129ef1000 waiting on condition [0x0000000000000000..0x0000000129eef3e0]
   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" daemon prio=9 tid=0x0000000101841000 nid=0x129dee000 waiting on condition [0x0000000000000000..0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Finalizer" daemon prio=8 tid=0x0000000101829800 nid=0x129ceb000 in Object.wait() [0x0000000129cea000..0x0000000129ceaad0]
   java.lang.Thread.State: WAITING (on object monitor)
	at java.lang.Object.wait(Native Method)
	- waiting on <0x000000010f73b138> (a java.lang.ref.ReferenceQueue$Lock)
	at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:116)
	- locked <0x000000010f73b138> (a java.lang.ref.ReferenceQueue$Lock)
	at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:132)
	at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:159)

"Reference Handler" daemon prio=10 tid=0x0000000101828800 nid=0x129be8000 in Object.wait() [0x0000000129be7000..0x0000000129be7ad0]
   java.lang.Thread.State: WAITING (on object monitor)
	at java.lang.Object.wait(Native Method)
	- waiting on <0x000000010f73b218> (a java.lang.ref.Reference$Lock)
	at java.lang.Object.wait(Object.java:485)
	at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:116)
	- locked <0x000000010f73b218> (a java.lang.ref.Reference$Lock)

"VM Thread" prio=9 tid=0x0000000101820800 nid=0x129ae5000 runnable 

"VM Periodic Task Thread" prio=10 tid=0x0000000101846000 nid=0x12a1fa000 waiting on condition 

"Exception Catcher Thread" prio=10 tid=0x0000000101802000 nid=0x100504000 runnable 
JNI global references: 782

Heap
 def new generation   total 2304K, used 1932K [0x0000000105000000, 0x0000000105290000, 0x000000010f6a0000)
  eden space 1984K,  88% used [0x0000000105000000, 0x00000001051b6708, 0x00000001051f0000)
  from space 320K,  55% used [0x0000000105240000, 0x000000010526c930, 0x0000000105290000)
  to   space 320K,   0% used [0x00000001051f0000, 0x00000001051f0000, 0x0000000105240000)
 tenured generation   total 5312K, used 4069K [0x000000010f6a0000, 0x000000010fbd0000, 0x0000000124400000)
   the space 5312K,  76% used [0x000000010f6a0000, 0x000000010fa99770, 0x000000010fa99800, 0x000000010fbd0000)
 compacting perm gen  total 21248K, used 18600K [0x0000000124400000, 0x00000001258c0000, 0x0000000129800000)
   the space 21248K,  87% used [0x0000000124400000, 0x000000012562a360, 0x000000012562a400, 0x00000001258c0000)
No shared spaces configured.