delphi多线程Tadoquery共享主Form1中的FADOConnection出错！

weismart

毕业设计中遇到多线程与数据库问题。
怀疑多线程中动态生成的N个Tadoquery共享主Form1中的Tadoconnection时会有问题，于是写测试代码来测试，结果确实如此，但又想不通测试代码为什么出错，请各位高手帮忙看一下。
//-----------主窗体放置一TADOconnection /Tmemo/Tbutton三个控件
//其中Tmemo用于显示从数据库中取得的时间
//Tbutton 用于生成n个的查询动作。

unit Unit1;
interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, DB, ADODB,unit2;

type
  TForm1 = class(TForm)
    Button1: TButton;
    ADOConnection1: TADOConnection; //TadoConnection作为线程中动态生成
                                    //TadoQuery的公用连接///
    Memo1: TMemo;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  TestThread:TMyThread;  //创建n个一模一样的线程
  TestThread2:tmythread; //与上面的一模一样///
  TEstThread3:Tmythread;
  TestThread4:Tmythread;
  TestThread5:Tmythread;
  TEstThread6:Tmythread;
  TestThread7:Tmythread;
  TestThread8:Tmythread;
implementation


{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
  TestThread:=TMyThread.Create(adoconnection1,memo1);
  Testthread2:=TMyThread.Create(adoconnection1,memo1);
  TEstThread3:=Tmythread.Create(adoconnection1,memo1);
  TestThread4:=Tmythread.Create(adoconnection1,memo1);
  TestThread5:=Tmythread.Create(adoconnection1,memo1);
  TEstThread6:=Tmythread.Create(adoconnection1,memo1);
  TestThread7:=Tmythread.Create(adoconnection1,memo1);
  TestThread8:=Tmythread.Create(adoconnection1,memo1);
end;

end.


//----------------线程单元---------------------------//

unit Unit2;
interface

uses
  Classes,DB,StdCtrls, ADODB,ActiveX;

type
  TMyThread = class(TThread)
  private
    FAdoQuery:TADOQuery;
    FMemory:Tmemo;
    FADOConnection:TADOConnection;

  protected
    procedure Execute; override;
  public
    constructor Create(adoconnection:TadoConnection;memory:TMemo);
    destructor destroy;
    procedure runsql;
  end;

implementation
constructor TMyThread.Create(adoconnection: TadoConnection; memory: TMemo);
begin
   CoInitialize(nil); //初始化ado
   inherited create(false);
   Fadoconnection:=adoconnection;
   Fadoquery:=Tadoquery.Create(nil);
   fadoquery.Connection:=fadoconnection;
   Fmemory:=memory;
   FreeOnTerminate:=True;
end;

destructor TMyThread.destroy;
begin
  Fadoquery.Free;
  CoUninitialize;
  inherited destroy;
end;

procedure TMyThread.Execute;
begin
  synchronize(runsql);
end;

procedure TMyThread.runsql;
var
  datetimestr:string;
begin
  datetimestr:= 'select to_char(sysdate,'''+'yyyymmdd HH24:MM:SS'''+') from dual';
  if not Fadoconnection.Connected then
  try
    FadoConnection.Open;  
  except
    Fmemory.Lines.Add('opendb error');
  end;
  try
   ////////------不要了 Fadoquery:=Tadoquery.Create(nil);
    Fadoquery.Connection:=fadoconnection;
    fadoquery.SQL.Clear ;
    fadoquery.Close;
    fadoquery.SQL.Add(datetimestr);
    fadoquery.open ;
    datetimestr:=fadoquery.Fields[0].AsString;
    fmemory.Lines.Add(datetimestr); //显示时间
  except
    Fmemory.Lines.Add('sql error');
  end;
end;

end.

按button1第七次后出错，结果如下
project project1.exe
ora-01000:超出打出光标最大值。

Memo1
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sql error
sql error
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sql error