synchdisk.h

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// synchdisk.h 
//      Data structures to export a synchronous interface to the raw 
//      disk device.
//
// Copyright (c) 1992-1993 The Regents of the University of California.
// All rights reserved.  See copyright.h for copyright notice and limitation 
// of liability and disclaimer of warranty provisions.

#include "copyright.h"

#ifndef SYNCHDISK_H
#define SYNCHDISK_H

#include "disk.h"
#include "synch.h"
#include "callback.h"

// The following class defines a "synchronous" disk abstraction.
// As with other I/O devices, the raw physical disk is an asynchronous device --
// requests to read or write portions of the disk return immediately,
// and an interrupt occurs later to signal that the operation completed.
// (Also, the physical characteristics of the disk device assume that
// only one operation can be requested at a time).
//
// This class provides the abstraction that for any individual thread
// making a request, it waits around until the operation finishes before
// returning.

class SynchDisk : public CallBackObj {
  public:
    SynchDisk();                        // Initialize a synchronous disk,
                                        // by initializing the raw Disk.
    ~SynchDisk();                       // De-allocate the synch disk data
    
    void ReadSector(int sectorNumber, char* data);
                                        // Read/write a disk sector, returning
                                        // only once the data is actually read 
                                        // or written.  These call
                                        // Disk::ReadRequest/WriteRequest and
                                        // then wait until the request is done.
    void WriteSector(int sectorNumber, char* data);
    
    void CallBack();                    // Called by the disk device interrupt
                                        // handler, to signal that the
                                        // current disk operation is complete.

  private:
    Disk *disk;                         // Raw disk device
    Semaphore *semaphore;               // To synchronize requesting thread 
                                        // with the interrupt handler
    Lock *lock;                         // Only one read/write request
                                        // can be sent to the disk at a time
};

#endif // SYNCHDISK_H

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