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SynchDisk CRC

Name:

 SynchDisk

Comment:

 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.

Collaborators:

Responsibilities: 

class SynchDisk {
  public:
    SynchDisk(char* name);              // 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 RequestDone();                 // 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
};