Delphi中多线程用Synchronize实现VCL数据同步显示

　　VCL实现同步方法就是调用线程类的Synchronize的过程，此过程需要一个无参数的procedure，故在此procedure中无法传递参数值，但可以通过类的成员来实现。在类的Execute中只须调用Synchronize就可以了。

 　　如果在线程中对VCL赋值操作，在连续执行多次以后，会报“Canvas  does not allow drawing”错误，这个错误可以由上述方法修复，把赋值操作让窗体主线程来完成。

　　关键在于对Synchronize参数的定义。定义一个无参数的procedure通过它来访问类的成员变量szName和nIndex。在类的重载Execute中调用Synchronize。

　　例证代码：

　　 1 

 2 procedure TRunningWatcher.Execute;
 3 begin
 4     {do some thing here}
 5     FreeOnTerminate := True;
 6     while (not Terminated) and (not Application.Terminated) do
 7     begin
 8        QueryPerformanceFrequency(CounterFrequency);
 9        QueryPerformanceCounter(EndCounter);
10        Synchronize(WatchAction); {必须让主线程来运行，否则会报"Canvas  does not allow drawing"错误}
11        Sleep(500);
12        if ThreadCount = 0 then {如果线程全部退出，需要做最后一次统计}
13        begin
14          Synchronize(WatchAction);
15          Self.Suspend;
16        end;
17     end;
18 end;
19 
20 {监视器显示统计信息}
21 procedure TRunningWatcher.WatchAction;
22 var
23   iSetCount:Integer;
24   dDiffTime,dPerSecond:Extended;
25 begin
26      iSetCount  := ISetValueCount;
27      dDiffTime := 0;
28      dPerSecond := 0;
29      if not LessThan(EndCounter, BeginCounter) then
30      begin
31         dDiffTime := (EndCounter-BeginCounter)/CounterFrequency*1000.0;
32         dPerSecond := dDiffTime/dDiffTime*1000;
33      end;
34      Self.mThreadCount.Caption      := IntToStr(list.Count);
35      Self.mThreadRun.Caption        := IntToStr(ThreadCount);
36      Self.mThreadTerminate.Caption  := IntToStr(list.Count-ThreadCount);
37      Self.mTotalCostTime.Caption    := FormatFloat('0.00', CalSumValueE(CallServerTimeArr, 0, iSetCount-1));
38      Self.mCallTimes.Caption        := IntToStr(iSetCount);
39      Self.mAvgCostTime.Caption      := FormatFloat('0.00', CalAvgValueE(CallServerTimeArr, 0, iSetCount-1));
40      Self.mMaxCostTime.Caption      := FormatFloat('0.00', CalcMaxValueE(CallServerTimeArr, 0, iSetCount-1));
41      Self.mMinCostTime.Caption      := FormatFloat('0.00', CalcMinValueE(CallServerTimeArr, 0, iSetCount-1));
42      Self.mRunTime.Caption          := FormatFloat('0.00', dDiffTime);
43      Self.mSynCallBack.Caption      := FormatFloat('0.00', dPerSecond);
44 end;

 

 程序说明：我这里定义了一些Tlabel的成员变量，根据构造函数来初始化成界面上的对应控件，在这里等同于界面上的label，在Execute函数中不停调用WatchAction过程，起先我的写法如下：

        QueryPerformanceFrequency(CounterFrequency);
2        QueryPerformanceCounter(EndCounter);
3        WatchAction; {必须让主线程来运行，否则会报"Canvas  does not allow drawing"错误}
4        Sleep(500);
5        if ThreadCount = 0 then {如果线程全部退出，需要做最后一次统计}
6        begin
7          WatchAction;
8          Self.Suspend;
9        end;

 

 在连续执行到9k次以上时，报“Canvas  does not allow drawing”错误。修改后解决问题：

 1        QueryPerformanceFrequency(CounterFrequency);

        QueryPerformanceCounter(EndCounter);
3        Synchronize(WatchAction); {必须让主线程来运行，否则会报"Canvas  does not allow drawing"错误}
4        Sleep(500);
5        if ThreadCount = 0 then {如果线程全部退出，需要做最后一次统计}
6        begin
7          Synchronize(WatchAction);
8          Self.Suspend;
9        end;