Mapping de fichier et tstream
Contenu du snippet
Cette unit contien un simple objet TSream surchargé pour employé le principe du mapping de fichier en mémoire de Windows. Il s'utilise comme un MemoryStream ou un FileSream
Source / Exemple :
unit MappedFileStream;
interface
uses
Windows,
SysUtils,
Classes;
type
TMappedFileStream = class(TStream)
private
hMapping : THandle; // Handle de l'objet file-mapping
FMemory : pByteArray;// Adresse de base du mapping
FHandle : THandle; // Handle du fichier ouvert pour le mapping
FPosition,
FSize : Integer;
public
// Enregistre les pages modifiées dans le fichier sur le disque
procedure Flush;
function Read(var Buffer; Count: Longint): Longint; override;
function Write(const Buffer; Count: Longint): Longint; override;
function Seek(const Offset: Int64; Origin: TSeekOrigin): Int64; override;
property Memory: pByteArray read FMemory;
property Position: Integer read FPosition;
property Size : Integer read FSize;
property Handle: THandle read FHandle;
constructor Create(FileName: string;
Mode: Word = fmOpenRead;
Rights: Cardinal = fmShareExclusive;
Offset: Cardinal = 0;
MaxSize: Cardinal = 0);
destructor Destroy; override;
published
{ Published declarations }
end;
implementation
procedure TMappedFileStream.Flush;
begin
FlushViewOfFile(FMemory, 0);
end;
function TMappedFileStream.Read(var Buffer; Count: Integer): Integer;
begin
if FPosition + Count > Size then Count := Size - FPosition;
move(FMemory[FPosition], Buffer, Count);
Result := Count;
end;
function TMappedFileStream.Write(const Buffer; Count: Longint): Longint;
begin
if FPosition + Count > Size then Count := Size - FPosition;
move(Buffer, FMemory[FPosition], Count);
Result := Count;
end;
function TMappedFileStream.Seek(const Offset: Int64; Origin: TSeekOrigin): Int64;
begin
Case Origin of
soBeginning: // Seek from the beginning of the resource. The seek operation moves to a specified position (offset), which must be greater than or equal to zero.
if Offset < FSize then FPosition := Offset else raise ERangeError.Create('');
soCurrent : // Seek from the current position in the resource. The seek operation moves to an offset from the current position (position + offset). The offset is positive to move forward, negative to move backward.
if FPosition + Offset < FSize then FPosition := FPosition + Offset else raise ERangeError.Create('');
soEnd : // Seek from the end of the resource. The seek operation moves to an offset from the end of the resource, where the offset is expressed as a negative value because it is moving toward the beginning of the resource.
if FSize - Offset >= 0 then FPosition := FSize - Offset else raise ERangeError.Create('');
end;
result := FPosition;
end;
constructor TMappedFileStream.Create(FileName: string;
Mode: Word = fmOpenRead;
Rights: Cardinal = fmShareExclusive;
Offset: Cardinal = 0;
MaxSize: Cardinal = 0);
var
dwDA, dwSM, dwCD, flP, dwVA: DWORD;
FileInfo: _BY_HANDLE_FILE_INFORMATION;
begin
// Initialise correctement les attributs de construction du mapping
case Mode of
fmCreate:
begin
dwCD := CREATE_ALWAYS;
dwDA := GENERIC_WRITE and GENERIC_READ;
dwVA := FILE_MAP_WRITE;
flP := PAGE_READWRITE;
end;
fmOpenRead:
begin
dwCD := OPEN_EXISTING;
dwDA := GENERIC_READ;
dwVA := FILE_MAP_READ;
flP := PAGE_READONLY;
end;
fmOpenWrite:
begin
dwCD := TRUNCATE_EXISTING;
dwDA := GENERIC_WRITE and GENERIC_READ;
dwVA := FILE_MAP_WRITE;
flP := PAGE_READWRITE;
end;
fmOpenReadWrite:
begin
dwCD := OPEN_EXISTING;
dwDA := GENERIC_WRITE and GENERIC_READ;
dwVA := FILE_MAP_WRITE;
flP := PAGE_READWRITE;
end;
end;
case Rights of
fmShareCompat or fmShareExclusive:
begin
dwSM := 0;
end;
fmShareDenyWrite:
begin
dwSM := FILE_SHARE_READ;
end;
fmShareDenyRead:
begin
dwSM := FILE_SHARE_WRITE;
end;
fmShareDenyNone:
begin
dwSM := FILE_SHARE_READ and FILE_SHARE_WRITE;
end;
end;
// Ouvre le fichier
FileName := FileName + #0; // Ajout du zero terminal
FHandle := CreateFile(@FileName[1], dwDA, dwSM, nil, dwCD, 0, 0);
inherited create;
if FHandle = INVALID_HANDLE_VALUE then raise Exception.Create('Erreur Windows N°' + IntToStr(GetLastError));
if MaxSize = 0 then begin
if not GetFileInformationByHandle(FHandle, FileInfo) then begin
CloseHandle(FHandle);
raise Exception.Create('Erreur Windows N°' + IntToStr(GetLastError));
end;
FSize := FileInfo.nFileSizeLow;
end else FSize := MaxSize;
hMapping := CreateFileMapping(FHandle, nil, flP, 0, FSize, nil);
if hMapping = INVALID_HANDLE_VALUE then begin
FileClose(FHandle);
raise Exception.Create('Erreur Windows N°' + IntToStr(GetLastError));
end;
FMemory := MapViewOfFile(hMapping, dwVA, 0, 0, FSize);
if FMemory = nil then begin
FileClose(FHandle);
CloseHandle(hMapping);
raise Exception.Create('Erreur Windows N°' + IntToStr(GetLastError));
end;
end;
destructor TMappedFileStream.Destroy;
begin
Flush;
UnMapViewOfFile(FMemory);
CloseHandle(hMapping);
CloseHandle(FHandle);
inherited destroy;
end;
end.
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