In my Application when I write text files (logs, traces, etc), I use TFileStream
class.
There are cases that I write the data in multithreaded environment, those are the steps:
1- Write Cache Data
2- For each 1000 lines I save to File.
3- Clear Data.
This process is repeated during all processing.
Problem Description:
With 16 threads, the system throws the following exception:
Access Violation - file already in use by another application.
I guess this is happening because that the handle used by one thread is not closed yet, when another thread needs to open.
I changed the architecture to the following: (bellow is the NEW implementation)
In the previous way, the TFileStream was created with FileName and Mode parameters, and destroyed closing the handle (I wasn't using TMyFileStream)
TMyFileStream = class(TFileStream)
public
destructor Destroy; override;
end;
TLog = class(TStringList)
private
FFileHandle: Integer;
FirstTime: Boolean;
FName: String;
protected
procedure Flush;
constructor Create;
destructor Destroy;
end;
destructor TMyFileStream.Destroy;
begin
//Do Not Close the Handle, yet!
FHandle := -1;
inherited Destroy;
end;
procedure TLog.Flush;
var
StrBuf: PChar; LogFile: string;
F: TFileStream;
InternalHandle: Cardinal;
begin
if (Text <> '') then
begin
LogFile:= GetDir() + FName + '.txt';
ForceDirectories(ExtractFilePath(LogFile));
if FFileHandle < 0 then
begin
if FirstTime then
FirstTime := False;
if FileExists(LogFile) then
if not SysUtils.DeleteFile(LogFile) then
RaiseLastOSError;
InternalHandle := CreateFile(PChar(LogFile), GENERIC_READ or GENERIC_WRITE, FILE_SHARE_READ, nil, CREATE_NEW, 0,0);
if InternalHandle = INVALID_HANDLE_VALUE then
RaiseLastOSError
else if GetLastError = ERROR_ALREADY_EXISTS then
begin
InternalHandle := CreateFile(PChar(LogFile), GENERIC_READ or GENERIC_WRITE, FILE_SHARE_READ, nil, OPEN_EXISTING, 0,0);
if InternalHandle = INVALID_HANDLE_VALUE then
RaiseLastOSError
else
FFileHandle := InternalHandle;
end
else
FFileHandle := InternalHandle;
end;
F := TMyFileStream.Create(FFileHandle);
try
StrBuf := PChar(Text);
F.Position := F.Size;
F.Write(StrBuf^, StrLen(StrBuf));
finally
F.Free();
end;
Clear;
end;
end;
destructor TLog.Destroy;
begin
FUserList:= nil;
Flush;
if FFileHandle >= 0 then
CloseHandle(FFileHandle);
inherited;
end;
constructor TLog.Create;
begin
inherited;
FirstTime := True;
FFileHandle := -1;
end;
There is another better way?
Is this implementation correct?
May I improve this?
My guess about the Handle was right?
All theads use the same Log object.
There is no reentrance, i checked! there is something wrong with the TFileStream.
The Access to the Add is synchronized, I mean, I used critical session, and when it reaches 1000 lines, Flush procedure is called.
P.S: I do not want third-party component, i want to create my own.