TADOQuery池

//==============================================================================
// TADOQuery池    咏南工作室        2008-10-06 14:22:35
//==============================================================================

unit UAdoQueryPool;

interface

uses
  SysUtils, Classes, DB, ADODB, Contnrs, Windows, ExtCtrls;

type
  RQueryParams=record
    QueryMin:Integer;   //池中对象最小数  10
    QueryMax:Integer;   //池中对象最大数  100
    TimerTime:Integer;  //清理程序启动的时间间隔 600000(10分钟)
  end;

type
  TAdoQueryPool = class(TComponent) //AdoQuery缓冲池类
  private
    fAdoQueryMin : Integer;
    fAdoQueryMax : Integer;
    fAdoQueryList : TComponentList;
    fCleanTimer : TTimer;
    fQueryParams:RQueryParams;
    procedure fCleanOnTime(sender : TObject); //按时整理缓冲池
    function fCreateADOQuery : TADOQuery;     //创建新的AdoQuery
    procedure fClean;                         //整理 （清理长时间不用的和长时间不归还的AdoQuery）
    { Private declarations }
  public
    { Public declarations }
    constructor Create(owner : TComponent;QueryParams:RQueryParams);
    function getAdoQuery : TADOQuery;             //取得空闲TADOQuery
    procedure returnAdoQuery(qry : TADOQuery);    //归还
end;

implementation

{ TAdoQueryPool }

constructor TAdoQueryPool.Create(owner: TComponent;QueryParams:RQueryParams);
var
  index : Integer;
  aAdoQuery : TADOQuery;
begin
  fQueryParams:=QueryParams;

  fAdoQueryMin := fQueryParams.QueryMin;
  fAdoQueryMax := fQueryParams.QueryMax;
  fAdoQueryList := TComponentList.Create(False);
  for index := 1 to fAdoQueryMin do
    fAdoQueryList.Add(fCreateADOQuery);

  if fCleanTimer = nil then
  begin
    fCleanTimer := TTimer.Create(Self);
    fCleanTimer.Name := 'MyCleanTimer1';
    fCleanTimer.Interval :=fQueryParams.TimerTime; //清理程序启动的时间间隔(10分钟)
    fCleanTimer.OnTimer := fCleanOnTime;
    fCleanTimer.Enabled := True;
  end;
end;

procedure TAdoQueryPool.fClean;
var
  iNow : Integer;   //当前时刻
  iCount : Integer; //List大小
  index : Integer;
begin
  iNow := GetTickCount;
  iCount := fAdoQueryList.Count;
  for index := iCount - 1 downto 0 do
  begin
    if TADOQuery(fAdoQueryList[index]).Tag > 0 then //若空闲
    begin
      if fAdoQueryList.Count > fAdoQueryMin then //若AdoQuery个数大于最小值
      begin
        TADOQuery(fAdoQueryList[index]).Free;
      end
      else if TAdoQuery(fAdoQueryList[index]).Tag < 0 then
      begin
        if iNow + TADOQuery(fAdoQueryList[index]).Tag > 10800000 then //被连续使用超过3小时的AdoQuery（很可能是死的），释放
        begin
          TADOQuery(fAdoQueryList[index]).Free;
          if fAdoQueryList.Count < fAdoQueryMin then//若小于缓冲池最小数目，则创建新的空闲AdoQuery
            fAdoQueryList.Add(fCreateADOQuery);
        end;
      end;
    end;
  end;
end;

procedure TAdoQueryPool.fCleanOnTime(sender: TObject);
begin
  fClean;
end;

function TAdoQueryPool.fCreateADOQuery: TADOQuery;
begin
  Result := TADOQuery.Create(Self);
  Result.Tag := GetTickCount; //空闲，开始计时(正数表示空闲)
end;

function TAdoQueryPool.getAdoQuery: TADOQuery;
var
  index : Integer;
begin
  Result := nil;
  for index := 0 to fAdoQueryList.Count - 1 do
  begin
    if TADOQuery(fAdoQueryList[index]).Tag > 0 then
    begin
      Result := TADOQuery(fAdoQueryList[index]);
      Result.Tag := - GetTickCount;  //使用开始计时 （负数表示正在使用）
    end;
  end;

  if (Result = nil) and (index < fAdoQueryMax) then//无空闲AdoQuery，而缓冲池数目小于允许最大数目（fAdoQueryMax），创建新的Adoquery
  begin
    Result := fCreateADOQuery;
    Result.Tag := - GetTickCount;    //使用,开始计时 （负数表示正在使用）
    fAdoQueryList.Add(Result);
  end;
end;

procedure TAdoQueryPool.returnAdoQuery(qry: TADOQuery);
begin
  if fAdoQueryList.IndexOf(qry) > -1 then
    qry.Tag := GetTickCount; //开始空闲计时
end;

end.