From: "Robert C. Martin" <u.n.c.l.e.b.o.b.@...>
Date: 2002-04-01T02:08:34+09:00
Subject: Multithreaded socket code.  Request for Comments

I'd appreciate any comments you might have regarding the following
multithreaded socket code.  I am particularly interested in whether
the use of the mutex to protect the array is appropriate, and in
whether killing the serviceThread is the right approach in the close
method.

The first batch of code is the SocketService module.  The second batch
contains the unit tests.

require 'socket'
require 'thread'

class SocketService
  def initialize()
    @threads = []
    @lock = Mutex.new
  end
  
  def serve(port, &action)
    @action = action
    @ropeSocket = TCPserver.open(port)
    @serviceThread = Thread.start {serviceTask}
  end
  
  def pendingSessions
    @threads.size
  end
  
  def serviceTask
    while true
      Thread.start(@ropeSocket.accept) {|s| serverTask(s)}
    end
  end
  
  def serverTask(s)
    @lock.synchronize {@threads << Thread.current}
    @action.call(s)
    s.close
    @lock.synchronize {@threads.delete(Thread.current)}
  end
  
  def close
    @serviceThread.kill
    @ropeSocket.close
    waitForServers
  end
  
  def waitForServers
    threads=nil
    @lock.synchronize {threads = @threads.dup}
    threads.each {|t| t.join}
  end
end

------------------------------------------

require 'Lapidary/TestCase'
require 'SocketService'

class TestSocketService< Lapidary::TestCase
  def setup
    @ss = SocketService.new()
    @connections = 0
  end
  
  def testOneConnection
    puts "testOneConnection"
    port = 999
    @ss.serve(port) {@connections += 1}
    connect(port)
    @ss.close()
    assertEqual(1, @connections)
  end
  
  def testManyConnections
    puts "testManyConnections"
    port = 999
    @ss.serve(port) {@connections += 1}
    10.times {connect(port)}
    @ss.close()
    assertEqual(10, @connections)
    assertEqual(0, @ss.pendingSessions)
  end
  
  def testSocketSend
    puts "testSocketSend"
    port = 999
    @ss.serve(port) do |serverSocket|
      serverSocket.write("hi")
    end
    
    clientSocket = TCPsocket.open("localhost", port)
    answer = clientSocket.gets
    clientSocket.close
    assertEqual("hi", answer)
    @ss.close()
  end
  
  # We should not be able to keep the service alive by hitting 
  # it with connections after we close it?
  def testCantKeepAliveByConnectingAfterClose
    puts "testCloseRaceCondition"
    port = 999
    
    #set up a service that waits for a message and then dies.
    @ss.serve(port) do |serverSocket|
      message = serverSocket.gets
    end
    
    #s1 is a connection to that service.
    s1 = TCPSocket.open("localhost", port)
    sleep(.1)
    
    #now start closing the server in a separate thread. It cannot
    #finish closing until s1 completes.
    Thread.start {@ss.close}
    sleep(.1)
    
    #try to connect to the dying server.
    s2=nil
    Thread.start {s2 = TCPSocket.open("localhost", port)}
    sleep(.1)
    assertEqual(nil, s2, "shouldn't have connected")
    assertNotEqual(nil, s1, "Should have connected")
    
    #Complete the s1 session.
    s1.write("testCloseRaceCondition");
    s1.close
    
    #collect the pending s2 connection
    testThread = Thread.current
    @ss.serve(port) {testThread.wakeup}
    Thread.stop
    assertNotEqual(nil, s2)  
    s2.close
    @ss.close
  end
  
  def testSessionCount
    puts "testSessionCount"
    port=999
    @ss.serve(port) do |serverSocket|
      message = serverSocket.gets
    end  
    
    s1 = nil;
    Thread.start {s1 = TCPSocket.open("localhost", port)}
    sleep(.2)
    assertEqual(1, @ss.pendingSessions);
    s1.write("testSessionCount");
    s1.close
    sleep(.2)
    assertEqual(0, @ss.pendingSessions)
    @ss.close
  end
  
  def connect(port)
    s = TCPsocket.open("localhost", port)
    sleep(.1)
    s.close
  end
end

require 'Lapidary/UI/Console/TestRunner'
puts "Starting Test"
Lapidary::UI::Console::TestRunner.run(TestSocketService)
Robert C. Martin  | "Uncle Bob"                   
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