In order to learn multithreading, I've created a thread inside a COM Thread (TRemoteDataModule
).
This is my Component Factory:
TComponentFactory.Create(ComServer, TServerConn2, Class_ServerConn2, ciMultiInstance, tmApartment);
Inside the Thread, I didn't needed to Call CoInitialize to use TADOQuery.Create
, .Open
... .Exec
I read that I need to initialize the COM library on a thread before you call any of the library functions except CoGetMalloc, to get a pointer to the standard allocator, and the memory allocation functions.
But in this case, the absence of CoInitialize didn't brought me any trouble.
Is this related with Thread Model?
Where can I Find the explanation for this subject?
UPDATE:
When I say INSIDE, it means inside the COM method context:
interface
type
TWorker = class(TThread);
TServerConn2 = class(TRemoteDataModule, IServerConn2)
public
procedure Method(); safecall;
end;
implementation
procedure TServerConn2.Method();
var W: TWorker;
begin
W := TWorkerTread.Create(Self);
end;
UPDATE 2:
The TADOConnection
used to connect to database are currently being created in the COM Thread context (TThread.Create constructor
). Although, TADOConnection.Open
and TADOQuery.Create/.Open
are both being performed inside TThread.Execute
.
UPDATE 3 - Simulacrum
Interface:
type
TServerConn2 = class;
TWorker = class(TThread)
private
FDB: TADOConnection;
FOwner: TServerConn2;
protected
procedure Execute; override;
public
constructor Create(Owner: TServerConn2);
destructor Destroy; override;
end;
TServerConn2 = class(TRemoteDataModule, IServerConn2)
ADOConnection1: TADOConnection;
procedure RemoteDataModuleCreate(Sender: TObject);
private
{ Private declarations }
protected
class procedure UpdateRegistry(Register: Boolean; const ClassID, ProgID: string); override;
procedure CheckException; safecall;
public
User, Pswd, Str: String;
Ok: Boolean;
end;
Implementation:
class procedure TServerConn2.UpdateRegistry(Register: Boolean; const ClassID, ProgID: string);
begin
if Register then
begin
inherited UpdateRegistry(Register, ClassID, ProgID);
EnableSocketTransport(ClassID);
EnableWebTransport(ClassID);
end else
begin
DisableSocketTransport(ClassID);
DisableWebTransport(ClassID);
inherited UpdateRegistry(Register, ClassID, ProgID);
end;
end;
{ TWorker }
constructor TWorker.Create(Owner: TServerConn2);
begin
inherited Create(False);
FreeOnTerminate := True;
FDB := TADOConnection.Create(nil);
FOwner := Owner;
end;
destructor TWorker.Destroy;
begin
FDB.Free;
FOwner.Ok := True;
inherited;
end;
procedure TWorker.Execute;
var Qry: TADOQuery;
begin
FDB.LoginPrompt := False;
FDB.ConnectionString := FOwner.Str;
FDB.Open(FOwner.User, FOwner.Pswd);
Qry := TADOQuery.Create(nil);
try
Qry.Connection := FDB;
Qry.LockType := ltReadOnly;
Qry.SQL.Text := 'SELECT TOP 1 * FROM MyTable';
Qry.Open;
finally
Qry.Free;
end;
end;
procedure TServerConn2.CheckException;
var W: TWorker;
begin
W := TWorker.Create(Self);
while not Ok do Sleep(100);
end;
procedure TServerConn2.RemoteDataModuleCreate(Sender: TObject);
begin
User := 'user';
Pswd := 'pass';
Str := ADOConnection1.ConnectionString;
end;
initialization
TComponentFactory.Create(ComServer, TServerConn2,
Class_ServerConn2, ciMultiInstance, tmApartment);
end.
UPDATE 4
The error should happen here:
function CreateADOObject(const ClassID: TGUID): IUnknown;
var
Status: HResult;
FPUControlWord: Word;
begin
asm
FNSTCW FPUControlWord
end;
Status := CoCreateInstance(ClassID, nil, CLSCTX_INPROC_SERVER or
CLSCTX_LOCAL_SERVER, IUnknown, Result);
asm
FNCLEX
FLDCW FPUControlWord
end;
if (Status = REGDB_E_CLASSNOTREG) then
raise Exception.CreateRes(@SADOCreateError) else
OleCheck(Status);
end;
By somehow (because of TComponentFactory
maybe?) CoCreateInstance
identifies that TWorker
is in the same context than TServerConn2
and don't raise errors?