在这篇文章中,delphi.net(prism)支持异步文件IO。Delphi(Native/VCL)也有异步文件IO类吗?
RTL/VCL中没有内置任何异步文件I/O的功能。顺便说一下,Delphi Prism的支持是基于.net框架而不是基于语言。
您可以直接使用Win32 API进行编码(这不太有趣),或者寻找Delphi包装器来实现API。就我所知,我不知道任何异步文件I/O的Delphi包装器,但它们必须存在。
你看过这段代码吗?http://pastebin.com/A2EERtyW
这是一个不错的异步文件I/O的开端,但我个人会写一个包装器来维护与VCL/RTL的兼容性,基于标准的TStream
类。
编辑2:这个也不错。 http://www.torry.net/vcl/filedrv/other/dstreams.zip
我在这里发布它,以防它从Pastebin上消失:
unit xfile;
{$I cubix.inc}
interface
uses
Windows,
Messages,
WinSock,
SysUtils,
Classes;
const
MAX_BUFFER = 1024 * 32;
type
TFileReadEvent = procedure(Sender: TObject; const Buffer; Count: Integer) of object;
TAsyncFile = class
private
FHandle: THandle;
FPosition: Cardinal;
FReadPending: Boolean;
FOverlapped: TOverlapped;
FBuffer: Pointer;
FBufferSize: Integer;
FOnRead: TFileReadEvent;
FEof: Boolean;
FSize: Integer;
function ProcessIo: Boolean;
procedure DoOnRead(Count: Integer);
function GetOpen: Boolean;
public
constructor Create(Filename: string; BufferSize: Integer = MAX_BUFFER);
destructor Destroy; override;
procedure BeginRead;
procedure Seek(Position: Integer);
procedure Close;
property OnRead: TFileReadEvent read FOnRead write FOnRead;
property Eof: Boolean read FEof;
property IsOpen: Boolean read GetOpen;
property Size: Integer read FSize;
end;
function ProcessFiles: Boolean;
implementation
var
Files: TList;
function ProcessFiles: Boolean;
var
i: Integer;
AsyncFile: TAsyncFile;
begin
Result := False;
for i := Files.Count - 1 downto 0 do
begin
AsyncFile := TAsyncFile(Files[i]);
Result := AsyncFile.ProcessIo or Result;
end;
end;
procedure Cleanup;
var
i: Integer;
AsyncFile: TAsyncFile;
begin
for i := Files.Count - 1 downto 0 do
begin
AsyncFile := TAsyncFile(Files[i]);
AsyncFile.Free;
end;
Files.Free;
end;
{ TAsyncFile }
constructor TAsyncFile.Create(Filename: string; BufferSize: Integer);
begin
Files.Add(Self);
FReadPending := False;
FBufferSize := BufferSize;
GetMem(FBuffer, FBufferSize);
FillMemory(@FOverlapped, SizeOf(FOverlapped), 0);
Cardinal(FHandle) := CreateFile(
PChar(Filename), // file to open
GENERIC_READ, // open for reading
0, // do not share
nil, // default security
OPEN_EXISTING, // open existing
FILE_ATTRIBUTE_NORMAL, //or // normal file
//FILE_FLAG_OVERLAPPED, // asynchronous I/O
0); // no attr. template
FSize := FileSeek(FHandle, 0, soFromEnd);
FileSeek(FHandle, 0, soFromBeginning);
FPosition := 0;
end;
destructor TAsyncFile.Destroy;
begin
Files.Remove(Self);
CloseHandle(FHandle);
FreeMem(FBuffer);
inherited;
end;
function TAsyncFile.ProcessIo: Boolean;
var
ReadCount: Cardinal;
begin
Result := False; Exit;
if not FReadPending then
begin
Exit;
end;
if GetOverlappedResult(FHandle, FOverlapped, ReadCount, False) then
begin
FReadPending := False;
DoOnRead(ReadCount);
end
else
begin
case GetLastError() of
ERROR_HANDLE_EOF:
begin
FReadPending := False;
FEof := True;
end;
ERROR_IO_PENDING:
begin
FReadPending := True;
end;
0:
begin
Result := True;
end;
end;
end;
end;
procedure TAsyncFile.BeginRead;
var
ReadResult: Boolean;
ReadCount: Cardinal;
begin
ReadCount := 0;
Seek(FPosition);
ReadResult := ReadFile(FHandle, FBuffer^, FBufferSize, ReadCount, nil);//@FOverlapped);
if ReadResult then
begin
FEof := False;
FReadPending := False;
FPosition := FPosition + ReadCount;
DoOnRead(ReadCount);
end
else
begin
case GetLastError() of
ERROR_HANDLE_EOF:
begin
FReadPending := False;
FEof := True;
end;
ERROR_IO_PENDING:
begin
FReadPending := True;
end;
end;
end;
end;
procedure TAsyncFile.DoOnRead(Count: Integer);
begin
if Assigned(FOnRead) then
begin
FOnRead(Self, FBuffer^, Count);
end;
end;
function TAsyncFile.GetOpen: Boolean;
begin
Result := Integer(FHandle) >= 0;
end;
procedure TAsyncFile.Close;
begin
FileClose(FHandle);
end;
procedure TAsyncFile.Seek(Position: Integer);
begin
FPosition := Position;
FileSeek(FHandle, Position, soFromBeginning);
end;
initialization
Files := Tlist.Create;
finalization
Cleanup;
end.