buffers.h

基于DOS系统下的多任务类库。Class DOS Thread provides a framework for writing DOS applications

//--------------------------------------------------------------------------
//
//      BUFFERS.H: header file for DOSMonitor-based bounded buffer.
//      Copyright (c) J.English 1993.
//      Author's address: [e-mail]
//
//      Permission is granted to use copy and distribute the
//      information contained in this file provided that this
//      copyright notice is retained intact and that any software
//      or other document incorporating this file or parts thereof
//      makes the source code for the library of which this file
//      is a part freely available.
//
//--------------------------------------------------------------------------
//
//      Revision history:
//      1.0     March 1993      Initial coding
//
//--------------------------------------------------------------------------

#ifndef __BUFFERS_H
#define __BUFFERS_H

#include "threads.h"

//--------------------------------------------------------------------------
//
//      Class BoundedBuffer.
//
//      This is a template for a DOSMonitor-based bounded buffer.
//      The constructor requires the size of the buffer as a parameter.
//      The member functions "get" and "put" allow individual data items
//      to be taken out of and put into the buffer.  The member function
//      "close" allows the buffer to be closed against further use.  The
//      member function "items" returns the number of items currently in
//      the buffer.
//
template<class T> class BoundedBuffer : public DOSMonitor
{
  public:
    BoundedBuffer (unsigned n)  : buffer(new T[n]), buffersize(n),
                                  count(0), inptr(0), outptr(0), closed(0)
                                { }
    ~BoundedBuffer ()           { delete [] buffer; }

    unsigned items ()           { return count; }

    int get (T& item);          // get an item from the buffer
    int put (const T& item);    // put an item into the buffer
    void close ();              // close buffer against further use

  private:
    DOSMonitorQueue full;
    DOSMonitorQueue empty;
    T* buffer;
    unsigned buffersize;
    unsigned count;
    unsigned inptr;
    unsigned outptr;
    unsigned closed;
};

//--------------------------------------------------------------------------
//
//      BoundedBuffer::get.
//
//      Get an item from the buffer.  The thread will be suspended on the
//      "empty" queue as long as the buffer is empty or until the buffer
//      is closed.  If the buffer is closed, the function will return 0.
//      Otherwise, the next item is extracted and the "inptr" is moved
//      to point to the next item.  Finally, any threads waiting while the 
//      buffer is full are resumed (since there is now an empty space in
//      the buffer) and the value 1 is returned to indicate success.
//
template <class T> int BoundedBuffer<T>::get (T& item)
{
    lock ();
    while (count == 0 && !closed)
        suspend (empty);        // await non-empty buffer
    if (count != 0)
    {   item = buffer [inptr++];
        inptr %= buffersize;
        count--;
        resume (full);          // awaken threads waiting for non-full buffer
    }
    unlock ();
    return !closed;
}


//--------------------------------------------------------------------------
//
//      BoundedBuffer::put.
//
//      Put an item into the buffer.  The thread will be suspended on the
//      "full" queue as long as the buffer is empty or until the buffer
//      is closed.  If the buffer is closed, the function will return 0.
//      Otherwise, the item is stored in the next available space and
//      "outptr" is moved to point to the next free space.  Finally,
//      any threads waiting while the buffer was empty are resumed (since
//      there is now an item in the buffer) and the value 1 is returned
//      to indicate success.
//
template <class T> int BoundedBuffer<T>::put (const T& item)
{
    lock ();
    while (count == buffersize && !closed)
        suspend (full);         // await non-full buffer
    if (count != buffersize)
    {   buffer [outptr++] = item;
        outptr %= buffersize;
        count++;
        resume (empty);         // awaken threads waiting for non-empty buffer
    }
    unlock ();
    return !closed;
}

//--------------------------------------------------------------------------
//
//      BoundedBuffer::close.
//
//      This function closes the buffer against further use.  The "closed"
//      flag is set and any suspended threads are resumed.  This is to guard
//      against situations where a thread might wait forever for an item
//      which never arrives, which would prevent the program from ever
//      terminating.
//
template <class T> void BoundedBuffer<T>::close ()
{
    lock ();
    closed = 1;
    resume (full);
    resume (empty);
    unlock ();
}

#endif