RWBufferedPageHeap (deprecated)

Module:  Essential Tools Module   Group:  File System Classes

RWBufferedPageHeapRWVirtualPageHeap

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• Synopsis
• Description
• Persistence
• Public Constructor
• Public Destructor
• Protected Member Functions
• Public Member Functions

Members

allocate() deallocate() dirty()

isValid() lock() RWBufferedPageHeap()

swapIn() swapOut() unlock()

~RWBufferedPageHeap()

#include <rw/bufpage.h>
(Abstract base class )

This is an abstract base class that represents an abstract page heap buffered through a set of memory buffers. It inherits from the abstract base class RWVirtualPageHeap, which represents an abstract page heap.

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NOTE -- RWBufferedPageHeap is deprecated.

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RWBufferedPageHeap will supply and maintain a set of memory buffers. Specializing classes should supply the actual physical mechanism to swap pages in and out of these buffers by supplying definitions for the pure virtual functions swapIn(RWHandle, void*) and swapOut(RWHandle, void*).

The specializing class should also supply appropriate definitions for the public functions allocate() and deallocate(RWHandle).

For a sample implementation of a specializing class, see class RWDiskPageHeap.

None

RWBufferedPageHeap(unsigned pgsize, unsigned nbufs=10);

Constructs a buffered page heap with page size pgsize. The number of buffers (each of size pgsize) that will be allocated on the heap will be nbufs. If there is insufficient memory to satisfy the request, then the state of the resultant object as returned by member function isValid() will be false, otherwise, true.

virtual
~RWBufferedPageHeap();

Deallocates all internal buffers.

virtual bool
swapIn(RWHandle h, void* buf)  = 0;
virtual bool
swapOut(RWHandle, h void* buf) = 0;

It is the responsibility of the specializing class to supply definitions for these two pure virtual functions. Function swapOut() should copy the page with handle h from the buffer pointed to by buf to the swapping medium. Function swapIn() should copy the page with handle h into the buffer pointed to by buf.

virtual RWHandle
allocate() = 0;

It is the responsibility of the specializing class to supply a definition for this pure virtual function. The specializing class should allocate a page and return a unique handle for it. It should return zero if it cannot satisfy the request. The size of the page is set by the constructor.

bool
isValid();

Returns true if self is in a valid state. A possible reason why the object might not be valid is insufficient memory to allocate the internal buffers.

virtual void
deallocate(RWHandle h);

Redefined from class RWVirtualPageHeap. It is never an error to call this function with argument zero. Even though this is not a pure virtual function, it is the responsibility of the specializing class to supply an appropriate definition for this function. All this definition does is release any buffers associated with the handle h. Just as the actual page allocation is done by the specializing class through virtual function allocate(), so must the actual deallocation be done by overriding deallocate().

virtual void
dirty(RWHandle h);

Redefined from class RWVirtualPageHeap.

virtual void*
lock(RWHandle h);

Redefined from class RWVirtualPageHeap.

virtual void
unlock(RWHandle h);

Redefined from class RWVirtualPageHeap.

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