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[英]Is it safe to instantiate a TThread-descendent from inside a thread?
[英]Is a Thread Safe field of TThread itself thread safe?
在此代码中:
TMyClass = class(TThread)
public
FInputBuffer : TThreadedQueue<TBytes>;
protected
procedure Execute; override;
end;
使用FInputBuffer(在TMyClass和其他类中)是否是线程安全的?
编辑:
样本使用:在TMyClass中:
procedure TMyClass.Execute;
var x :TBytes;
begin
inherited;
FInputBuffer:= TThreadedQueue<TBytes>.Create;
while not Terminated do begin
if FInputBuffer.QueueSize > 0 then begin
x:= FInputBuffer.PopItem;
//some code to use x
end;
end;
FInputBuffer.Free;
end;
在其他班级:
var MyClass :TMyClass ;
procedure TForm1.btn1Click(Sender: TObject);
var x :TBytes;
begin
//set x
MyClass.FInputBuffer.PushItem(x);
end;
如果FInputBuffer
是在线程开始运行之前在线程构造函数中创建的 ,并且在线程运行完成之后在线程析构函数中释放的 ,则是的,当TMyClass
对象仍然存在时,从其他线程对其进行访问是线程安全的,因为TThreadedQueue
为其内部内容提供了自己的线程安全性。 如果MyClass
变量在调用btn1Click()
时有效,那么您所显示的是对多线程队列的完全有效使用。
但是,如果FInputBuffer
是在Execute()
内部创建的 ,则它不是线程安全的,因为btn1Click()
可能会在创建FInputBuffer
之前在线程开始运行之前尝试访问队列。 这就是为什么您需要在构造函数中创建FInputBuffer
原因,例如:
TMyClass = class(TThread)
public
FInputBuffer: TThreadedQueue<TBytes>;
constructor Create(ACreateSuspended: Boolean); override;
destructor Destroy; override;
protected
procedure Execute; override;
end;
constructor TMyClass.Create(ACreateSuspended: Boolean);
begin
inherited;
FInputBuffer := TThreadedQueue<TBytes>.Create;
end;
destructor TMyClass.Destroy;
begin
FInputBuffer.Free;
inherited;
end;
procedure TMyClass.Execute;
var
x: TBytes;
begin
while not Terminated do begin
if FInputBuffer.QueueSize > 0 then begin
x := FInputBuffer.PopItem;
// some code to use x
end;
end;
end;
如果要在Execute()
内部创建FInputBuffer
,则线程应公开在实际创建FInputBuffer
之后设置的标志/信号,并且在设置了该标志/信号之前,没有其他代码可以尝试访问FInputBuffer
。 创建线程实例的代码应先等待该标志/信号,然后再将控制权返回给其余代码,例如:
TMyClass = class(TThread)
public
FInputBuffer: TThreadedQueue<TBytes>;
FInputBufferCreated: TEvent;
constructor Create(ACreateSuspended: Boolean); override;
destructor Destroy; override;
protected
procedure Execute; override;
procedure DoTerminate; override;
end;
constructor TMyClass.Create(ACreateSuspended: Boolean);
begin
inherited;
FInputBufferCreated := TEvent.Create(nil, True, False, '');
end;
destructor TMyClass.Destroy;
begin
FInputBufferCreated.Free;
inherited;
end;
procedure TMyClass.Execute;
var
x: TBytes;
begin
FInputBuffer := TThreadedQueue<TBytes>.Create;
FInputBufferCreated.SetEvent;
while not Terminated do begin
if FInputBuffer.QueueSize > 0 then begin
x := FInputBuffer.PopItem;
// some code to use x
end;
end;
end;
procedure TMyClass.DoTerminate;
begin
if FInputBufferCreated <> nil then
FInputBufferCreated.ResetEvent;
FreeAndNil(FInputBuffer);
inherited;
end;
。
var
MyClass: TMyClass = nil;
procedure TForm1.StartBufferThread;
var
I: Integer;
begin
MyClass := TMyClass.Create(False);
if MyClass.FInputBufferCreated.WaitFor(2500) <> wrSignaled then
begin
MyClass.Terminate;
MyClass.WaitFor;
FreeAndNil(MyClass);
raise Exception.Create('MyClass.FInputBuffer not created after 2.5 seconds!');
end;
end;
procedure TForm1.btn1Click(Sender: TObject);
var
x: TBytes;
begin
//set x
if MyClass <> nil then
MyClass.FInputBuffer.PushItem(x);
end;
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