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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?
在此代碼中:
TMyClass = class(TThread)
public
FInputBuffer : TThreadedQueue<TBytes>;
protected
procedure Execute; override;
end;
使用FInputBuffer(在TMyClass和其他類中)是否是線程安全的?
編輯:
樣本使用: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;
在其他班級:
var MyClass :TMyClass ;
procedure TForm1.btn1Click(Sender: TObject);
var x :TBytes;
begin
//set x
MyClass.FInputBuffer.PushItem(x);
end;
如果FInputBuffer
是在線程開始運行之前在線程構造函數中創建的 ,並且在線程運行完成之后在線程析構函數中釋放的 ,則是的,當TMyClass
對象仍然存在時,從其他線程對其進行訪問是線程安全的,因為TThreadedQueue
為其內部內容提供了自己的線程安全性。 如果MyClass
變量在調用btn1Click()
時有效,那么您所顯示的是對多線程隊列的完全有效使用。
但是,如果FInputBuffer
是在Execute()
內部創建的 ,則它不是線程安全的,因為btn1Click()
可能會在創建FInputBuffer
之前在線程開始運行之前嘗試訪問隊列。 這就是為什么您需要在構造函數中創建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()
內部創建FInputBuffer
,則線程應公開在實際創建FInputBuffer
之后設置的標志/信號,並且在設置了該標志/信號之前,沒有其他代碼可以嘗試訪問FInputBuffer
。 創建線程實例的代碼應先等待該標志/信號,然后再將控制權返回給其余代碼,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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