From: Joel VanderWerf <vjoel@...>
Date: 2008-03-16T05:13:48+09:00
Subject: Re: How to make net-ping thread safe?

Joel VanderWerf wrote:
> In icmp.rb, the problem seems to be that it uses process ID as the ICMP 
> packet ID, so it is impossible to tell which ECHO REPLY packet 
> corresponds to which request (if multiple requests come from one process).

On second thought, the problem could be solved in icmp.rb by using the 
sequence number to separate requests, and keeping the sequence number in 
an ICMP class var instead of instance vars. Here's a patch that seems to 
make your original code work correctly (detecting some hosts up and some 
down).

--- 
/usr/local/lib/ruby/gems/1.8/gems/net-ping-1.2.2/lib/net/ping/icmp.rb 
    2008-01-23 19:46:14.000000000 -0800
+++ net/ping/icmp.rb    2008-03-15 13:09:55.000000000 -0700
@@ -24,7 +24,6 @@
        def initialize(host=nil, port=nil, timeout=5)
           raise 'requires root privileges' if Process.euid > 0

-         @seq = 0
           @bind_port = 0
           @bind_host = nil
           @data_size = 56
@@ -37,6 +36,11 @@
           super(host, port, timeout)
           @port = nil # This value is not used in ICMP pings.
        end
+
+      @seq = 0
+      def self.next_seq
+        @seq = (@seq + 1) % 65536
+      end

        # Sets the number of bytes sent in the ping method.
        #
@@ -73,14 +77,14 @@
              socket.bind(saddr)
           end

-         @seq = (@seq + 1) % 65536
+         seq = ICMP.next_seq
           pstring = 'C2 n3 A' << @data_size.to_s
           timeout = @timeout

           checksum = 0
-         msg = [ICMP_ECHO, ICMP_SUBCODE, checksum, @pid, @seq, 
@data].pack(pstring)
+         msg = [ICMP_ECHO, ICMP_SUBCODE, checksum, @pid, seq, 
@data].pack(pstring)
           checksum = checksum(msg)
-         msg = [ICMP_ECHO, ICMP_SUBCODE, checksum, @pid, @seq, 
@data].pack(pstring)
+         msg = [ICMP_ECHO, ICMP_SUBCODE, checksum, @pid, seq, 
@data].pack(pstring)

           start_time = Time.now

@@ -101,7 +105,7 @@
                 end

                 pid = nil
-               seq = nil
+               rcv_seq = nil

                 data, sender  = socket.recvfrom(1500)
                 port, host    = Socket.unpack_sockaddr_in(sender)
@@ -110,15 +114,15 @@
                 case type
                    when ICMP_ECHOREPLY
                       if data.length >= 28
-                        pid, seq = data[24, 4].unpack('n3')
+                        pid, rcv_seq = data[24, 4].unpack('n3')
                       end
                    else
                       if data.length > 56
-                        pid, seq = data[52, 4].unpack('n3')
+                        pid, rcv_seq = data[52, 4].unpack('n3')
                       end
                 end

-               if pid == @pid && seq == @seq && type == ICMP_ECHOREPLY
+               if pid == @pid && rcv_seq == seq && type == ICMP_ECHOREPLY
                    bool = true
                 end
              }


-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407