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Network CRC

Name:

 Network

Comment:

 The following class defines a physical network device. The network is capable of delivering fixed sized packets, in order but unreliably, to other machines connected to the network.

The "reliability" of the network can be specified to the constructor. This number, between 0 and 1, is the chance that the network will lose a packet. Note that you can change the seed for the random number generator, by changing the arguments to RandomInit() in Initialize(). The random number generator is used to choose which packets to drop.

Collaborators:

Responsibilities: 

class Network {
  public:
    Network(NetworkAddress addr, double reliability,
          VoidFunctionPtr readAvail, VoidFunctionPtr writeDone, int callArg);
                                // Allocate and initialize network driver
    ~Network();                 // De-allocate the network driver data

    void Send(PacketHeader hdr, char* data);
                                // Send the packet data to a remote machine,
                                // specified by "hdr".  Returns immediately.
                                // "writeHandler" is invoked once the next
                                // packet can be sent.  Note that writeHandler
                                // is called whether or not the packet is
                                // dropped, and note that the "from" field of
                                // the PacketHeader is filled in automatically
                                // by Send().

    PacketHeader Receive(char* data);
                                // Poll the network for incoming messages.
                                // If there is a packet waiting, copy the
                                // packet into "data" and return the header.
                                // If no packet is waiting, return a header
                                // with length 0.

    void SendDone();            // Interrupt handler, called when message is
                                // sent
    void CheckPktAvail();       // Check if there is an incoming packet

  private:
    NetworkAddress ident;       // This machine's network address
    double chanceToWork;        // Likelihood packet will be dropped
    int sock;                   // UNIX socket number for incoming packets
    char sockName[32];          // File name corresponding to UNIX socket
    VoidFunctionPtr writeHandler; // Interrupt handler, signalling next packet
                                //      can be sent.
    VoidFunctionPtr readHandler;  // Interrupt handler, signalling packet has
                                //      arrived.
    int handlerArg;             // Argument to be passed to interrupt handler
                                //   (pointer to post office)
    bool sendBusy;              // Packet is being sent.
    bool packetAvail;           // Packet has arrived, can be pulled off of
                                //   network
    PacketHeader inHdr;         // Information about arrived packet
    char inbox[MaxPacketSize];  // Data for arrived packet
};