RWDiskPageHeap(3C++) RWDiskPageHeap(3C++)
NameRWDiskPageHeap - Rogue Wave library class
Synopsis
#include <rw/diskpage.h>
unsigned nbufs;
unsigned pagesize;
RWDiskPageHeap heap("filename", nbufs, pagesize) ;
Description
Class RWDiskPageHeap is a specializing type of buffered page heap. It
swaps its pages to disk as necessary.
Persistence
None
Example
In this example, 100 nodes of a linked list are created and strung
together. The list is then walked, confirming that it contains 100
nodes. Each node is a single page. The "pointer" to the next node is
actually the handle for the next page.
#include <rw/diskpage.h>
#include <rw/rstream.h>
struct Node {
int key;
RWHandle next;
};
RWHandle head = 0;
const int N = 100; // Exercise 100 Nodes
main() {
// Construct a disk-based page heap with page size equal
// to the size of Node and with 10 buffers:
RWDiskPageHeap heap(0, 10, sizeof(Node));
// Build the linked list:
for (int i=0; i<N; i++){
RWHandle h = heap.allocate();
Node* newNode = (Node*)heap.lock(h);
newNode->key = i;
newNode->next = head;
head = h;
heap.dirty(h);
heap.unlock(h);
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RWDiskPageHeap(3C++) RWDiskPageHeap(3C++)
}
// Now walk the list:
unsigned count = 0;
RWHandle nodeHandle = head;
while(nodeHandle){
Node* node = (Node*)heap.lock(nodeHandle);
RWHandle nextHandle = node->next;
heap.unlock(nodeHandle);
heap.deallocate(nodeHandle);
nodeHandle = nextHandle;
count++;
}
cout << "List with " << count << " nodes walked.0;
return 0;
}
Program output:
List with 100 nodes walked.
Public Constructor
RWDiskPageHeap(const char* filename = 0,
unsigned nbufs = 10,
unsigned pgsize = 512);
Constructs a new disk-based page heap. The heap will use a file with
filename filename, otherwise it will negotiate with the operating system
for a temporary filename. The number of buffers, each the size of the
page size, will be nbufs. No more than this many pages can be locked at
any one time. The size of each page is given by pgsize. To see whether
a valid RWDiskPageHeap has been constructed, call member function
isValid().
Public Destructor
virtual
~RWDiskPageHeap();
Returns any resources used by the disk page heap back to the operating
system. All pages should have been deallocated before the destructor is
called.
Public Member Functions
virtual RWHandle
allocate();
Redefined from class RWVirtualPageHeap. Allocates a page off the disk
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page heap and returns a handle for it. If there is no more space (for
example, the disk is full) then returns zero.
virtual void
deallocate(RWHandle h);
Redefined from class RWBufferedPageHeap. Deallocate the page associated
with handle h. It is not an error to deallocate a zero handle.
virtual void
dirty(RWHandle h);
Inherited from RWBufferedPageHeap.
RWBoolean
isValid() const;
Returns TRUE if this is a valid RWDiskPageHeap.
virtual void*
lock(RWHandle h);
Inherited from RWBufferedPageHeap.
virtual void
unlock(RWHandle h);
Inherited from RWBufferedPageHeap.
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