Multithreading in Libraries using ADO

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June 9th, 2009, 08:54 AM

ibiglari

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Multithreading in Libraries using ADO

Hi;
I'm creating an application which connects to some medical instruments and gathers data. The application itself does nothing more than looking in a designated folder to load instruments. Each instrument is encapsulated in a DLL, and has a function which loops and reads the RS232 port, and write the data to a MSSQL2000 database. Because of this loop, which looks like this:
repeat
Sleep(500);
GetDataFromPort;
ParseData;
if AbortLoop then // AbortLoop is set by a button on a form
Break;
until False;
the application is almost completely blocked, and the CPU usage is about 100 %. I'm looking for a way to run each loop in a separate thread.
I have a simple problem. "CoInitialize() has not been called"
I have called it in my host application, and in my library. But I'm still getting this error. Any Idea?

June 9th, 2009, 12:40 PM

th0r1000

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From what I can tell from that piece of code you are in a loop that will in fact take up a lot of processing on the CPU, I would rather use a timer component and put that code in the trigger method excluding the repeat..until part.

June 9th, 2009, 01:20 PM

ibiglari

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I cannot do that because it would require me to modify the code of about 95 libraries. That's why I'm trying to spawn each library in a new thread in the host application

June 9th, 2009, 02:57 PM

clivew

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Quote:

I cannot do that because it would require me to modify the code of about 95 libraries.

Seems like there is something awfully wrong with your code or the components you are using.
What happened to inheritance?

BTW: Why do you think threads will help?
I believe that sleep statement is still going to absorb time.
Are you sure that all your code is thread safe and that the DLLs are re-entrant?

June 9th, 2009, 03:44 PM

ibiglari

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I'm not using any components; I open the ports with CreateFile.
Each library is completely stand alone and thread safe, but I don't know what re-entrant means.

June 9th, 2009, 05:37 PM

clivew

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Quote:

Originally Posted by ibiglari

I'm not using any components; I open the ports with CreateFile.
Each library is completely stand alone and thread safe, but I don't know what re-entrant means.

Then I don't understand your environment. Perhaps you can give a more complete explanation.

You said (I thought) that your code was loading instruments contained in third party DLLs.

Can you clarify which is your code, which are the libraries and which are the DLLs
and what you have source to and what you only have an API for.

Perhaps that will help us help you.
What are the gauges measuring?

June 10th, 2009, 01:47 AM

ibiglari

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Quote:

Originally Posted by clivew

There's no third party library. Both the host application and libraries are mine.

I can not post attachments in here; if you tell me how to send some source files, I'll post the host application and one of the libraries.

June 10th, 2009, 11:20 PM

clivew

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Quote:

Originally Posted by ibiglari

I will leave this to someone else.
I am not really getting a feel for what you are doing.
What about the DLLs?
What do you mean by a library?
Is it a unit a class or ??

If they are all yours, why do you have to change 95 of them?
I don't know enough about what you are doing; but it seems like you need to do some serious refactoring with an inheritance tree.

Good luck.

June 11th, 2009, 07:26 AM

ibiglari

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I try to describe my application in more details. Sorry if the information I provided was not clear.

There's a host application named "Transfer.exe". It looks in a folder named "Instruments" for files matching the following pattern: "*.INS". Each ".INS" file is a library which exports this functions:

Code:

function OpenPort(APort: Byte;
                  ABaudRate: Integer;
                  ADataSize: Byte;
                  AParity: Byte;
                  AStopBits: Byte): Boolean; export;

procedure ClosePort; export;

procedure ShowConfigDlg(ADataSource, ADataBase: ShortString); export;

procedure ShowAboutDlg; export;

procedure Communicate(ADataSource, ADataBase: ShortString;
                      APrefix: ShortString; AHandle: HWND;
                      ATimeOut: Cardinal); export;

function GetInstrumentClass: Byte; export;

function GetDescription: ShortString; export;

For each file, the host application creates an instance of a class which is declared like this:

Code:

type
  TGetInstrumentName = function(AAppHandle: HWND): ShortString;
  TGetDescription = function: ShortString;
  TGetInstrumentClass = function: Byte;
  TOpenPort = function(APort: Byte;
                       ABaudRate: Integer;
                       ADataSize: Byte;
                       AParity: Byte;
                       AStopBits: Byte): Boolean;
  TCommunicate = procedure(ADataSource, ADataSet: ShortString; APrefix: ShortString; AHandle: HWND; ATimeOut: Cardinal);
  TClosePort = procedure();
  TShowConfigDlg = procedure(ADataSource, ADataSet: ShortString);
  TShowAboutDlg = procedure;

type
{$IFDEF MultiThread}
  TTransferModule = class(TThread)
{$ELSE}
  TTransferModule = class(TObject)
{$ENDIF}
  private
    LibHandle: HWND;

    _GIN: TGetInstrumentName;
    _GD: TGetDescription;
    _GIC: TGetInstrumentClass;
    _OP: TOpenPort;
    _Comm: TCommunicate;
    _CP: TClosePort;
    _SCD: TShowConfigDlg;
    _SAD: TShowAboutDlg;
  public
    LibFile: String;
{$IFDEF MultiThread}
    procedure Execute; override;
{$ELSE}
    procedure Execute;
{$ENDIF}

    function GetInstrumentName: ShortString;
    function GetDescription: ShortString;
    function GetInstrumentClass: Byte;
    function OpenPort(APort: Byte;
                      ABaudRate: Integer;
                      ADataSize: Byte;
                      AParity: Byte;
                      AStopBits: Byte): Boolean;
    procedure ClosePort;
    procedure ShowConfigDlg;
    procedure ShowAboutDlg;
    constructor Create(ALibFile: String);
  end;

Each function has a body which looks like this:

Code:

procedure TTransferModule.ShowAboutDlg;
begin
  @_SAD := GetProcAddress(LibHandle, 'ShowAboutDlg');
  _SAD;
end;

When the user invokes the Communicate command in the host application, this code is executed:

Code:

procedure TdlgTransfer.btnConnectClick(Sender: TObject);
var
  Parity: Byte;
begin
  APrefix := cbSerial.Text;
  ATimeOut := StrToInt(cbTimeOut.Text);

  Parity := NOPARITY;

  case cbParity.ItemIndex of
    1: Parity := EVENPARITY;
    2: Parity := ODDPARITY;
  end;

  if not CurrentModule.OpenPort(cbPort.ItemIndex + 1, StrToInt(cbBaudRate.Text), StrToInt(cbDataSize.Text), Parity, cbStopBit.ItemIndex) then
    raise Exception.Create('Connection Failed');
{$IFDEF MultiThread}
  CurrentModule.Resume;
{$ELSE}
  CurrentModule.Execute;
{$ENDIF}
end;

The communicate function which contains the loop is defined in a library with an extension of ".INS" like this:

Code:

procedure Communicate(ADataSource, ADataBase: ShortString; APrefix: ShortString; AHandle: HWND; ATimeOut: Cardinal); export;
var
  AbortLoop: Boolean;

  procedure CallBack(ALine: ShortString);
  var
    CopyData: TCopyDataStruct;
  begin
    with CopyData do
    begin
      dwData := 0;
      cbData := SizeOf(ALine);
      lpData := @ALine;
    end;
    SendMessage(AHandle, WM_USER, dlgResults.Handle, Integer(@COPYDATA));

    Application.ProcessMessages;
    AbortLoop := dlgResults.AbortLoop;
  end;

var
{some local variables}
begin
  dmData := TdmData.Create(nil);
  OldHandle := Application.Handle;
  try
    Application.Handle := AppHandle;
    dmData.OpenConnection(ADataSource, ADataBase);
    AbortLoop := False;
    dlgResults := TdlgResults.Create(nil);
    try
      if not dlgResults.Visible then
        dlgResults.Show
      else
        dlgResults.BringToFront;
      repeat
        Buffer := '';

        FillChar(PR, SizeOf(PR), 0);
        repeat
          CallBack('');
        until (ReadFromSerial(Port, TimeOut) = STX) or AbortLoop;
        if AbortLoop then
          Break;
        repeat
          c := ReadFromSerial(Port, TimeOut);
          if (c <> ETX) and (c <> #0) then
            Buffer := Buffer + c;
          CallBack('');
        until (c = ETX) or AbortLoop;
        if AbortLoop then
          Break;
        WriteToSerial(Port, ACK, TimeOut);
        {process the data}
        MessageBeep(MB_OK);
      until False;
    finally
      ClosePort;
      dlgResults.Release;
    end;
  finally
    CallBack(#27);
    ClosePort;
    dmData.Free;
    Application.Handle := OldHandle;
  end;
end;

Now, if I declare the conditional define MultiThread, I get an error when I try to create my DataModule in the "*.INS" file. The error says "CoInitialize has not been called". I tried to call it at the initialization section of my first unit in the "*.INS" file, but I had no chance.

Hope this makes my question a little more clear

#10

June 11th, 2009, 01:08 PM

clivew

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Quote:

I tried to call it at the initialization section of my first unit in the "*.INS" file, but I had no chance.

You need to call it when you initialize each thread and call CoUnInitialize before you close each thread.

A lot of your other code looks very unconventional also.
Not sure why you have all those DLLs or why you suffix them with .INS but that is none of my business.

#11

June 11th, 2009, 04:01 PM

ibiglari

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So I need to call CoInitialize and CoUnintialize in my host application?

#12

June 11th, 2009, 08:22 PM

clivew

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Quote:

Originally Posted by ibiglari

So I need to call CoInitialize and CoUnintialize in my host application?

In each thread.

#13

June 15th, 2009, 07:03 AM

ibiglari

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:-)

I did call CoInitialize() at the beginning of Communicate() procedure, and CoUninitialize() at the finally block. Everything seems to work fine, but I guess I need to send a message back to the host application indicating that the procedure is quitting.
Thank you for your help :-)

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