我正在使用WaitForMultipleObjects
函数来等待多个线程的完成,但是我做错了,因为结果不是预期的
看到这个示例代码
type
TForm1 = class(TForm)
Memo1: TMemo;
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
end;
TFoo = class(TThread)
private
Factor: Double;
procedure ShowData;
protected
procedure Execute; override;
constructor Create(AFactor : Double);
end;
var
Form1: TForm1;
implementation
Uses
Math;
{$R *.dfm}
{ TFoo }
constructor TFoo.Create(AFactor: Double);
begin
inherited Create(False);
Factor := AFactor;
FreeOnTerminate := True;
end;
procedure TFoo.Execute;
const
Max=100000000;
var
i : Integer;
begin
inherited;
for i:=1 to Max do
Factor:=Sqrt(Factor);
Synchronize(ShowData);
end;
procedure TFoo.ShowData;
begin
Form1.Memo1.Lines.Add(FloatToStr(Factor));
end;
procedure TForm1.Button1Click(Sender: TObject);
const
nThreads=5;
Var
tArr : Array[1..nThreads] of TFoo;
hArr : Array[1..nThreads] of THandle;
i : Integer;
rWait : Cardinal;
begin
for i:=1 to nThreads do
begin
tArr[i]:=TFoo.Create(Pi*i);
hArr[i]:=tArr[i].Handle;
end;
repeat
rWait:= WaitForMultipleObjects(nThreads, @hArr, True, 100);
Application.ProcessMessages;
until rWait<>WAIT_TIMEOUT;
//here I want to show this message when all the threads are terminated
Memo1.Lines.Add('Wait done');
end;
end.
这是演示应用程序的当前输出
1
Wait done
1
1
1
1
但我想要这样的东西
1
1
1
1
1
Wait done
如何必须使用
WaitForMultipleObjects
函数来等待所有线程终止? 最佳答案
修复:删除FreeOnTerminate。
当您仍然需要句柄时,您的代码将导致线程被释放。那是一个大错误,您可能会在代码中的其他地方遇到访问冲突,或者从WaitFormMultipleObjects返回错误返回代码。
释放TThread时,TThread.handle变得无效,这将尽早终止您的等待循环,因为该句柄不再有效。如果您在后台将TThread释放后尝试访问TThread,也可能会遇到访问访问冲突,因此,我认为最好在已知的时间有意释放它们。
将线程句柄用作事件句柄可以很好地工作,但是在线程终止线程时不要使用FreeOnTerminate释放线程,因为这会过早地破坏句柄。
我也同意那些说用Application.Processmessages进行繁忙等待循环的做法是很丑陋的。还有其他方法可以做到这一点。
unit threadUnit2;
interface
uses Classes, SyncObjs,Windows, SysUtils;
type
TFoo = class(TThread)
private
FFactor: Double;
procedure ShowData;
protected
procedure Execute; override;
constructor Create(AFactor : Double);
destructor Destroy; override;
end;
procedure WaitForThreads;
implementation
Uses
Forms,
Math;
procedure Trace(msg:String);
begin
if Assigned(Form1) then
Form1.Memo1.Lines.Add(msg);
end;
{ TFoo }
constructor TFoo.Create(AFactor: Double);
begin
inherited Create(False);
FFactor := AFactor;
// FreeOnTerminate := True;
end;
destructor TFoo.Destroy;
begin
inherited;
end;
procedure TFoo.Execute;
const
Max=100000000;
var
i : Integer;
begin
inherited;
for i:=1 to Max do
FFactor:=Sqrt(FFactor);
Synchronize(ShowData);
end;
procedure TFoo.ShowData;
begin
Trace(FloatToStr(FFactor));
end;
procedure WaitForThreads;
const
nThreads=5;
Var
tArr : Array[1..nThreads] of TFoo;
hArr : Array[1..nThreads] of THandle;
i : Integer;
rWait : Cardinal;
begin
for i:=1 to nThreads do
begin
tArr[i]:=TFoo.Create(Pi*i);
hArr[i]:=tArr[i].handle; // Event.Handle;
end;
repeat
rWait:= WaitForMultipleObjects(nThreads, @hArr[1],{waitAll} True, 150);
Application.ProcessMessages;
until rWait<>WAIT_TIMEOUT;
Sleep(0);
//here I want to show this message when all the threads are terminated
Trace('Wait done');
for i:=1 to nThreads do
begin
tArr[i].Free;
end;
end;
end.