network.h

Go to the documentation of this file.

#ifndef NETWORK_H
#define NETWORK_H

#include "copyright.h"
#include "utility.h"

typedef int NetworkAddress;  


class PacketHeader {
  public:
    NetworkAddress to;      // Destination machine ID
    NetworkAddress from;    // source machine ID
    unsigned length;        // bytes of packet data, excluding the 
                // packet header (but including the 
                // MailHeader prepended by the post office)
};

#define MaxWireSize     64  // largest packet that can go out on the wire
#define MaxPacketSize   (MaxWireSize - sizeof(struct PacketHeader)) 
                // data "payload" of the largest packet


// 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.

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
};

#endif // NETWORK_H