datasnap对象池
{
之前说到中间层通过向客户端暴露方法的方式提供服务,实现数据库数据的读取和更新。方法调用的方式,其潜在的意义,就是说中间层不保存客户端状态信息,就像WEB服务一样,客户端需要自己保存自己的状态信息。进一步说,就是中间层具体提供方法的业务对象实例,不是也不应该专属于某个客户端,它应该能够为不同的客户端调用提供服务。如果我们把业务对象实例放到对象池中集中存放,调用方法时随用随取,方法结束即放回池中。这样就可以实现业务对象实例服务于不同的客户端调用请求。更重要的是,利用对象池,能够最大化服务器各种资源的使用效率,而且对客户端的响应也更快了,因为业务对象实例早就创建好了,取来即用。
其实,DataSnap构架,已经为我们的这种构想提供了现实支持。简单的说,就是改造工厂类(TDSServerClass),把LifeCycle属性改为Invocation方式;在OnCreateInstance事件中从对象池中取业务类对象实例;在OnDestroyInstance事件中把业务类对象实例放回对象池。
...
procedure TsmMainForm.dssMethodsCreateInstance(
DSCreateInstanceEventObject: TDSCreateInstanceEventObject);
begin
DSCreateInstanceEventObject.ServerClassInstance := ServerMethodsPool.LockPoolObject;
end;
procedure TsmMainForm.dssMethodsDestroyInstance(
DSDestroyInstanceEventObject: TDSDestroyInstanceEventObject);
begin
ServerMethodsPool.UnlockPoolObject(TPersistent(DSDestroyInstanceEventObject.ServerClassInstance));
end;
...
当然,还有对象池类的创建和释放,也很简单,例如:
procedure TsmMainForm.FormCreate(Sender: TObject);
begin
ServerMethodsPool := ObjPoolMgr.TPoolManager.Create;
ServerMethodsPool.InstanceClass := uServerMethods.TPooledDM;
end;
procedure TsmMainForm.FormDestroy(Sender: TObject);
begin
ServerMethodsPool.Free;
end;
下面就是如何实现对象池技术的问题。实现对象池并不复杂,另有两个问题需要注意:
1、多线程。中间层TDSTCPServerTransport对象提供的是多线程服务,允许同时有多个客户端请求。所以对象池类的实现,要考虑多线程情况下公共对象或变量的访问冲突问题。
2、内存泄漏。业务类的基类,采用TDataModule、TComponent或者TPersistent都可以,但不要采用TDSServerModule,因为若采用此基类,TDSServerClass在Invocation方式下会产生内存泄漏。
}
unit ObjPoolMgr;
interface
uses
Classes, SyncObjs, SysUtils, DSServer, DateUtils;
type
PServerObject = ^TServerObject;
TServerObject = record
ServerObject: TPersistent;
InUse: Boolean;
end;
TPoolManager = class
private
FCriticalSection: TCriticalSection;
FServerObjects: TList;
private
FMaxCount: Integer;
FInstanceClass: TPersistentClass;
function CreateNewInstance: TPersistent; inline;
procedure SetInstanceClass(const Value: TPersistentClass);
public
constructor Create(ACapicity:Integer=30); override;
destructor Destroy; override;
function Lock: TPersistent;
procedure Unlock(var Value: TPersistent);
public
property InstanceClass: TPersistentClass read FInstanceClass write SetInstanceClass;
property MaxCount:Integer read FMaxCount;
end;
var
ObjPool: TPoolManager;
implementation
constructor TPoolManager.Create(ACapicity:Integer=30);
begin
FMaxCount :=ACapicity;
FServerObjects := TList.Create;
FCriticalSection := TCriticalSection.Create;
end;
destructor TPoolManager.Destroy;
var
I: Integer;
begin
for I := 0 to FServerObjects.Count - 1 do
begin
PServerObject(FServerObjects[i]).ServerObject.Free;
FreeMem(PServerObject(FServerObjects[i]));
end;
FServerObjects.Free;
FCriticalSection.Free;
inherited Destroy;
end;
procedure TPoolManager.SetInstanceClass(const Value: TPersistentClass);
begin
FInstanceClass := Value;
end;
function TPoolManager.CreateNewInstance: TPersistent;
var
p: PServerObject;
Component: TComponent;
begin
if not Assigned(FInstanceClass) then Raise Exception.Create('Not specify class of instance!');
FCriticalSection.Enter;
try
if FInstanceClass.InheritsFrom(TComponent) then
begin
Component := FInstanceClass.NewInstance as TComponent;
Component.Create(nil);
Result := Component;
end
else
Result := FInstanceClass.Create;
New(p);
p.ServerObject := Result;
p.InUse := True;
FServerObjects.Add(p);
finally
FCriticalSection.Leave;
end;
end;
function TPoolManager.Lock: TPersistent;
var
i: Integer;
begin
FCriticalSection.Enter;
try
for i := 0 to FServerObjects.Count - 1 do
begin
if not PServerObject(FServerObjects[I]).InUse then
begin
PServerObject(FServerObjects[I]).InUse := True;
Result := PServerObject(FServerObjects[i]).ServerObject;
Exit;
end;
end;
finally
FCriticalSection.Leave;
end;
if FServerObjects.Count < MaxCount then
Result := CreateNewInstance
else
Result := nil;
end;
procedure TPoolManager.Unlock(var Value: TPersistent);
var
i: Integer;
begin
FCriticalSection.Enter;
try
for i := 0 to FServerObjects.Count - 1 do
begin
if Value = PServerObject(FServerObjects[i]).ServerObject then
begin
PServerObject(FServerObjects[i]).InUse := False;
Value := nil;
Break;
end;
end;
finally
FCriticalSection.Leave;
end;
end;
initialization
ObjPool := TPoolManager.Create();
finalization
FreeAndNil(objpool);
end.
本文来自博客园,作者:{咏南中间件},转载请注明原文链接:https://www.cnblogs.com/hnxxcxg/archive/2012/02/11/2347149.html