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

{监视器显示统计信息}
procedure TRunningWatcher.WatchAction;
var
iSetCount:Integer;
dDiffTime,dPerSecond:Extended;
begin
iSetCount := ISetValueCount;
dDiffTime := 0;
dPerSecond := 0;
if not LessThan(EndCounter, BeginCounter) then
begin
dDiffTime := (EndCounter-BeginCounter)/CounterFrequency*1000.0;
dPerSecond := dDiffTime/dDiffTime*1000;
end;
Self.mThreadCount.Caption := IntToStr(list.Count);
Self.mThreadRun.Caption := IntToStr(ThreadCount);
Self.mThreadTerminate.Caption := IntToStr(list.Count-ThreadCount);
Self.mTotalCostTime.Caption := FormatFloat('0.00', CalSumValueE(CallServerTimeArr, 0, iSetCount-1));
Self.mCallTimes.Caption := IntToStr(iSetCount);
Self.mAvgCostTime.Caption := FormatFloat('0.00', CalAvgValueE(CallServerTimeArr, 0, iSetCount-1));
Self.mMaxCostTime.Caption := FormatFloat('0.00', CalcMaxValueE(CallServerTimeArr, 0, iSetCount-1));
Self.mMinCostTime.Caption := FormatFloat('0.00', CalcMinValueE(CallServerTimeArr, 0, iSetCount-1));
Self.mRunTime.Caption := FormatFloat('0.00', dDiffTime);
Self.mSynCallBack.Caption := FormatFloat('0.00', dPerSecond);
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);
QueryPerformanceCounter(EndCounter);
WatchAction; {必须让主线程来运行，否则会报"Canvas does not allow drawing"错误}
Sleep(500);
if ThreadCount = 0 then {如果线程全部退出，需要做最后一次统计}
begin
WatchAction;
Self.Suspend;
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：

QueryPerformanceFrequency(CounterFrequency);

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