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unit dbf_pgcfile;
// paged, cached file
interface
{$I dbf_common.inc}
{$ifdef USE_CACHE}
uses
Classes,
SysUtils,
dbf_common,
dbf_avl,
dbf_pgfile;
type
PPageInfo = ^TPageInfo;
TPageInfo = record
TimeStamp: Cardinal;
Modified: Boolean;
Data: Char;
end;
TCachedFile = class(TPagedFile)
private
FPageTree: TAvlTree;
FUseTree: TAvlTree;
FTimeStamp: Cardinal;
FPageInfoSize: Integer;
FCacheSize: Integer;
FMaxPages: Cardinal;
function GetTimeStamp: Cardinal;
procedure UpdateTimeStamp(RecNo: Integer; Data: PPageInfo);
procedure PageDeleted(Sender: TAvlTree; Data: PData);
procedure UpdateMaxPages;
function AddToCache(RecNo: Integer; Buffer: Pointer): PPageInfo;
protected
procedure SetRecordSize(NewValue: Integer); override;
procedure SetCacheSize(NewSize: Integer);
public
constructor Create;
destructor Destroy; override;
procedure CloseFile; override;
procedure Flush; override;
function ReadRecord(RecNo: Integer; Buffer: Pointer): Integer; override;
procedure WriteRecord(RecNo: Integer; Buffer: Pointer); override;
property CacheSize: Integer read FCacheSize write SetCacheSize;
end;
{$endif}
implementation
{$ifdef USE_CACHE}
constructor TCachedFile.Create;
begin
inherited;
FPageTree := TAvlTree.Create;
FPageTree.OnDelete := PageDeleted;
FUseTree := TAvlTree.Create;
FPageInfoSize := 0;
FTimeStamp := 0;
FCacheSize := 256 * 1024;
end;
destructor TCachedFile.Destroy;
begin
Flush;
FPageTree.Free;
FUseTree.Free;
FPageTree := nil;
FUseTree := nil;
inherited;
end;
procedure TCachedFile.Flush;
begin
if FPageTree <> nil then
begin
FPageTree.Clear;
FUseTree.Clear;
end;
FTimeStamp := 0;
end;
procedure TCachedFile.CloseFile;
begin
// flush modified pages to disk
Flush;
// now we can safely close
inherited;
end;
procedure TCachedFile.SetRecordSize(NewValue: Integer);
begin
inherited;
// first flush all pages, restart caching with new parameters
Flush;
// calculate size of extra data of pagetree
FPageInfoSize := SizeOf(TPageInfo) - SizeOf(Char) + RecordSize;
UpdateMaxPages;
end;
procedure TCachedFile.SetCacheSize(NewSize: Integer);
begin
if FCacheSize <> NewSize then
begin
FCacheSize := NewSize;
UpdateMaxPages;
end;
end;
procedure TCachedFile.UpdateMaxPages;
begin
if RecordSize = 0 then
FMaxPages := 0
else
FMaxPages := FCacheSize div RecordSize;
end;
function TCachedFile.GetTimeStamp: Cardinal;
begin
Result := FTimeStamp;
Inc(FTimeStamp);
end;
procedure TCachedFile.PageDeleted(Sender: TAvlTree; Data: PData);
begin
// data modified? write to disk
if PPageInfo(Data^.ExtraData)^.Modified then
inherited WriteRecord(Data^.ID, @PPageInfo(Data^.ExtraData)^.Data);
// free cached page mem
FreeMem(Data^.ExtraData);
end;
function TCachedFile.AddToCache(RecNo: Integer; Buffer: Pointer): PPageInfo;
var
oldData: PData;
begin
// make sure there is a free page in the cache
while FPageTree.Count >= FMaxPages do
begin
// no free space, find oldest page
oldData := FUseTree.Lowest;
// remove from cache
FPageTree.Delete(Integer(oldData^.ExtraData));
FUseTree.Delete(oldData^.ID);
end;
// add to cache
GetMem(Result, FPageInfoSize);
Result^.TimeStamp := GetTimeStamp;
Result^.Modified := false;
Move(Buffer^, Result^.Data, RecordSize);
FPageTree.Insert(RecNo, Result);
FUseTree.Insert(Result^.TimeStamp, Pointer(RecNo));
end;
procedure TCachedFile.UpdateTimeStamp(RecNo: Integer; Data: PPageInfo);
begin
// update time used
FUseTree.Delete(Data^.TimeStamp);
Data^.TimeStamp := GetTimeStamp;
FUseTree.Insert(Data^.TimeStamp, Pointer(RecNo));
end;
function TCachedFile.ReadRecord(RecNo: Integer; Buffer: Pointer): Integer;
var
Data: PPageInfo;
begin
// only cache when we do not need locking
if NeedLocks then
begin Result := inherited ReadRecord(RecNo, Buffer) end else begin
// do we have this page in cache?
Data := PPageInfo(FPageTree.Find(RecNo));
if Data <> nil then
begin
// copy from cache
Move(Data^.Data, Buffer^, RecordSize);
UpdateTimeStamp(RecNo, Data);
Result := RecordSize;
end else begin
// not yet in cache
Result := inherited ReadRecord(RecNo, Buffer);
// add
if Result > 0 then
AddToCache(RecNo, Buffer);
end;
end;
end;
procedure TCachedFile.WriteRecord(RecNo: Integer; Buffer: Pointer);
var
Data: PPageInfo;
begin
// only cache when we do not need locking
if NeedLocks then
begin inherited end else begin
// do we have this page in cache?
Data := PPageInfo(FPageTree.Find(RecNo));
if Data <> nil then
begin
// copy to cache
Move(Buffer^, Data^.Data, RecordSize);
UpdateTimeStamp(RecNo, Data);
end else begin
// add
Data := AddToCache(RecNo, Buffer);
// notify we've added a page
UpdateCachedSize(CalcPageOffset(RecNo+PagesPerRecord));
end;
Data^.Modified := true;
end;
end;
{$endif} // USE_CACHE
end.
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