Hi, I was writing a quick Relay class and ran into a problem. Objects of this class act between two ports and log every TCP/IP that is sent between those ports - according to a specific protocol (in this simple example the first 8 characters contain the length of the data that will follow) These are the important methods of the class. All objects are local to the object and not shared between other objects. def start @server = TCPServer.new(l_h, l_p) @client = TCPSocket.new(r_h, r_p) loop do Thread.start(@server.accept) do |s| # handshake(s) client_to_server(s) server_to_client(s) end end end def client_to_server(s) Thread.new do loop do len = @client.recv(8) msg = @client.recv(len.to_i) @logfile.puts("Received " + msg) s.write(len) s.write(msg) end end end def server_to_client(s) Thread.new do loop do len = s.recv(8) msg = s.recv(len.to_i) @logfile.puts("Sent " + msg) @client.write(len) @client.write(msg) end end end My problem is that the file operations (@logfile.puts) are not performed immediately. When I check the file while communication is passing by, it is incomplete, sometimes even empty. Only when I kill the connection contained in @server.accept is the file properly flushed and is all traffic put into it. I don't understand why this happens. Why does @logfile.puts not happen immediately while @client.write and s.write do? I can't see why this would have anything to do with thread safety. Putting a mutex lock/unlock around the file operation didn't really do anything (I didn't really expect that to work either) Can anybody tell me what is happening here?
on 2009-04-28 17:19
on 2009-04-28 17:51
On 28.04.2009 17:19, Maarten Mortier wrote: > def start > end > end > end > immediately while @client.write and s.write do? > I can't see why this would have anything to do with thread safety. > > Putting a mutex lock/unlock around the file operation didn't really do > anything (I didn't really expect that to work either) > > Can anybody tell me what is happening here? You see the effect of IO buffering which indeed does not have anything to do with multi threading. You basically have two options to remedy that 1. use @client.sync = true for automatic flushing after every write operation 2. manually invoke #flush Independent from that you should take measures to make writing to the logfile thread safe. One option would be to have a reserved writer thread which pulls log messages from a Queue and writes them to the file. Another alternative is your approach (synchronization). Kind regards robert
on 2009-04-28 18:57
Robert Klemme wrote: > You see the effect of IO buffering Thanks! Maarten