141 lines
5.3 KiB
C++
141 lines
5.3 KiB
C++
// post.h
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// Data structures for providing the abstraction of unreliable,
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// ordered, fixed-size message delivery to mailboxes on other
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// (directly connected) machines. Messages can be dropped by
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// the network, but they are never corrupted.
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//
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// The US Post Office delivers mail to the addressed mailbox.
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// By analogy, our post office delivers packets to a specific buffer
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// (MailBox), based on the mailbox number stored in the packet header.
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// Mail waits in the box until a thread asks for it; if the mailbox
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// is empty, threads can wait for mail to arrive in it.
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//
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// Thus, the service our post office provides is to de-multiplex
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// incoming packets, delivering them to the appropriate thread.
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//
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// With each message, you get a return address, which consists of a "from
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// address", which is the id of the machine that sent the message, and
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// a "from box", which is the number of a mailbox on the sending machine
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// to which you can send an acknowledgement, if your protocol requires
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// this.
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//
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// Copyright (c) 1992-1993 The Regents of the University of California.
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// All rights reserved. See copyright.h for copyright notice and limitation
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// of liability and disclaimer of warranty provisions.
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#include "copyright.h"
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#ifndef POST_H
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#define POST_H
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#include "network.h"
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#include "synchlist.h"
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// Mailbox address -- uniquely identifies a mailbox on a given machine.
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// A mailbox is just a place for temporary storage for messages.
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typedef int MailBoxAddress;
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// The following class defines part of the message header.
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// This is prepended to the message by the PostOffice, before the message
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// is sent to the Network.
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class MailHeader {
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public:
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MailBoxAddress to; // Destination mail box
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MailBoxAddress from; // Mail box to reply to
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unsigned length; // Bytes of message data (excluding the
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// mail header)
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};
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// Maximum "payload" -- real data -- that can included in a single message
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// Excluding the MailHeader and the PacketHeader
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#define MaxMailSize (MaxPacketSize - sizeof(MailHeader))
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// The following class defines the format of an incoming/outgoing
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// "Mail" message. The message format is layered:
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// network header (PacketHeader)
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// post office header (MailHeader)
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// data
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class Mail {
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public:
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Mail(PacketHeader pktH, MailHeader mailH, const void *msgData);
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// Initialize a mail message by
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// concatenating the headers to the data
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PacketHeader pktHdr; // Header appended by Network
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MailHeader mailHdr; // Header appended by PostOffice
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char data[MaxMailSize]; // Payload -- message data
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};
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// The following class defines a single mailbox, or temporary storage
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// for messages. Incoming messages are put by the PostOffice into the
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// appropriate mailbox, and these messages can then be retrieved by
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// threads on this machine.
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class MailBox:public dontcopythis {
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public:
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MailBox(); // Allocate and initialize mail box
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~MailBox(); // De-allocate mail box
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void Put(PacketHeader pktHdr, MailHeader mailHdr, const void *data);
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// Atomically put a message into the mailbox
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void Get(PacketHeader *pktHdr, MailHeader *mailHdr, void *data);
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// Atomically get a message out of the
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// mailbox (and wait if there is no message
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// to get!)
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private:
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SynchList *messages; // A mailbox is just a list of arrived messages
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};
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// The following class defines a "Post Office", or a collection of
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// mailboxes. The Post Office is a synchronization object that provides
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// two main operations: Send -- send a message to a mailbox on a remote
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// machine, and Receive -- wait until a message is in the mailbox,
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// then remove and return it.
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//
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// Incoming messages are put by the PostOffice into the
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// appropriate mailbox, waking up any threads waiting on Receive.
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class PostOffice:public dontcopythis {
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public:
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PostOffice(NetworkAddress addr, double reliability, int nBoxes);
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// Allocate and initialize Post Office
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// "reliability" is how many packets
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// get dropped by the underlying network
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~PostOffice(); // De-allocate Post Office data
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void Send(PacketHeader pktHdr, MailHeader mailHdr, const void *data);
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// Send a message to a mailbox on a remote
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// machine. The fromBox in the MailHeader is
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// the return box for ack's.
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void Receive(int box, PacketHeader *pktHdr,
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MailHeader *mailHdr, void *data);
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// Retrieve a message from "box". Wait if
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// there is no message in the box.
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void PostalDelivery(); // Wait for incoming messages,
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// and then put them in the correct mailbox
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void PacketSent(); // Interrupt handler, called when outgoing
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// packet has been put on network; next
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// packet can now be sent
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void IncomingPacket(); // Interrupt handler, called when incoming
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// packet has arrived and can be pulled
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// off of network (i.e., time to call
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// PostalDelivery)
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private:
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Network *network; // Physical network connection
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NetworkAddress netAddr; // Network address of this machine
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MailBox *boxes; // Table of mail boxes to hold incoming mail
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int numBoxes; // Number of mail boxes
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Semaphore *messageAvailable;// V'ed when message has arrived from network
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Semaphore *messageSent; // V'ed when next message can be sent to network
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Lock *sendLock; // Only one outgoing message at a time
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};
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#endif
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