The Delphi Bug List

Cause:

Delphi sets FWaitStat to True before issuing the Execute transaction to the DDEML. It uses the TIMEOUT_ASYNC flag in the Execute, so it expects to get a DDE callback of type XTYP_XACT_COMPLETE when the server finishes the transaction. The DDE callback routine should then call TDdeClientConv.XactComplete which sets FWaitStat to false.
The problem is that Delphi is using the DDEML DDESetUserHandle and DDEQueryConvInfo functions to store the TDdeClientConv pointer in the hUser member of the CONVINFO structure maintained by the DDEML. In the DDE callback handler it uses DDEQueryConvInfo to get the TDdeClientConv associated with the callback, passing it the transaction id for XTYP_XACT_COMPLETE callbacks and QID_SYNC for all other callbacks. Unfortunately it only calls DDESetUserHandle with QID_SYNC (when the conversation is opened), and never calls it with the transaction id for async transactions, so it never finds the TDdeClientConv for XTYP_XACT_COMPLETE callbacks.

function DdeMgrCallBack(CallType, Fmt: UINT; Conv: HConv; hsz1, hsz2: HSZ;
  Data: HDDEData; Data1, Data2: DWORD): HDDEData; stdcall;
var
  ci: TConvInfo;
  ddeCli: TComponent;
  ddeSrv: TDdeSrvrConv;
  ddeObj: TComponent;
  xID: Integer;
begin
  Result := 0;
  case CallType of
    XTYP_CONNECT:         Result := HDdeData(ddeMgr.AllowConnect(hsz2, hsz1));
    XTYP_WILDCONNECT:     Result := ddeMgr.AllowWildConnect(hsz2, hsz1);
    XTYP_CONNECT_CONFIRM: ddeMgr.Connect(Conv, hsz1, Boolean(Data2));
  end;
  if Conv <> then
  begin
    ci.cb := sizeof(TConvInfo);
// FIX TO BUG - COMMENT OUT NEXT 3 LINES
//    if CallType = XTYP_XACT_COMPLETE then 
//      xID := Data1
//    else xID := QID_SYNC;

And here is some:
On 2 July 1999, Randy Shaw submitted the following:
Found a possible fix for bug # 22 on Deja News. I just typed in DdeSetUserHandle for the keywords and *delphi* for the forum and found this fix by Chad Crawley way back in March of 1997.

I'm successfully using this fix with version 3.02 of delphi but he was using it for version 2 so I suspect this will work for all versions from 2 to 3.02 but I have not confirmed this. The bug fix on your site does not work for me.

Modify the TDdeClientConv.ExecuteMacro function in ddeman.pas to the following.

{ Modified to set the user handle for the transaction.  The DdeMsgCallBack  }
{ function will not reset FWaitStat without this handle, effectively        }
{ disabling your connection after the first macro execution.  CIC  03/10/97 }
{ by Chad Crawley <snafo_AT_kcnet.com> }
function TDdeClientConv.ExecuteMacro(Cmd: PChar; waitFlg: Boolean): Boolean;
var
  hszCmd: HDDEData;
  hdata: HDDEData;
  ddeRslt: LongInt;
  bSetHandle: Boolean;
begin
  Result := False;
  if (FConv = 0) or FWaitStat then Exit;
  hszCmd := DdeCreateDataHandle(ddeMgr.DdeInstId, Cmd, StrLen(Cmd) + 1,
    0, 0, FDdeFmt, 0);
  if hszCmd = 0 then Exit;
  if waitFlg = True then FWaitStat := True;
  hdata := DdeClientTransaction(Pointer(hszCmd), -1, FConv, 0, FDdeFmt,
     XTYP_EXECUTE, TIMEOUT_ASYNC, @ddeRslt);
  bSetHandle := DdeSetUserHandle(FConv, ddeRslt, DWord(Self));
  if (hdata = 0) or (bSetHandle = False) then FWaitStat := False
  else Result := True;
end;

Neither of the 2 fixes work for D5 is my experience.
I do not have a solution for this.

Neither of the 2 fixes work for D5 is my experience.
I do not have a solution for this.