多线程访问数据

时间:2013-01-12 15:53:58

标签: multithreading delphi delphi-xe3

我有一个我写过的应用程序,我有三个帖子。线程1,2和3.

两个数字1和2的列表。

1号线将数据插入1号列表。

第2号线从第1号列表中获取数据。

第2号线将数据插入第2号清单。

第3号线从第2号清单中获取数据。

如果线程同时运行占用了大量CPU。可以在列表中输入数据,第二个,不需要第三个运行线程。

如何通知插入新数据列表中的线程并且需要开始处理新的数据处理呢?

与您联系的技巧和有效方式?

非常感谢。

2 个答案:

答案 0 :(得分:2)

这是一个从三个线程中添加list1和list2中的值的示例。

每次将值放入列表时,都会触发Event,处理此事件的线程会拉出列表中的最后一个值并清除事件标志。

在清除事件标志之前,不能将新值放入列表中。

中间线程对新值进行中间存储,而不是停止第一个线程。

所有事件都是等待的,因此可以让cpu保持畅通。

列表是线程安全的。

program Project62;

{$APPTYPE CONSOLE}

uses
  System.SysUtils,
  System.Classes,
  System.SyncObjs,
  System.Generics.Collections;

Type
  TMyThread1 = Class(TThread)
    private
      fMySyncAddList : TSimpleEvent;
      fMyList : TThreadList<Integer>;
      fAddVal : Integer;
    public
      Constructor Create(ASyncAddList: TSimpleEvent; AList: TThreadList<Integer>);
      procedure Execute; override;
  End;
  TMyThread2 = Class(TThread)
    private
      fMySyncAddList1,fMySyncAddList2 : TSimpleEvent;
      fMyList1,fMyList2 : TThreadList<Integer>;
      fAddVal : Integer;
    public
      Constructor Create(ASyncAddList1,ASyncAddList2: TSimpleEvent; AList1,AList2 : TThreadList<Integer>);
      procedure Execute; override;
  End;
  TMyThread3 = Class(TThread)
    private
      fMySyncAddList2 : TSimpleEvent;
      fMyList2 : TThreadList<Integer>;
      fAddVal : Integer;
    public
      Constructor Create(ASyncAddList2: TSimpleEvent; AList2 : TThreadList<Integer>);
      procedure Execute; override;
  End;


{ TMyThread1 }

constructor TMyThread1.Create( ASyncAddList : TSimpleEvent; AList: TThreadList<Integer>);
begin
  Inherited Create(false);
  fMySyncAddList := AsyncAddList;
  fMyList := AList;

end;

procedure TMyThread1.Execute;
var
  stateAcknowledged : boolean;
begin
  stateAcknowledged := true;
  while (not Terminated) do
  begin
    if stateAcknowledged then
    begin // Do some work and adda a value to list1
      fAddVal := Random(100);
      fMyList.Add(fAddVal);
      fMySyncAddList.SetEvent; // Signal a new addition
      stateAcknowledged := false;
      //ShowVal;
      Sleep(1000);
    end
    else begin
      stateAcknowledged := (fMySyncAddList.WaitFor(100) <> wrSignaled);
    end;
  end;
end;

{ TMyThread2 }

constructor TMyThread2.Create(ASyncAddList1, ASyncAddList2: TSimpleEvent;
  AList1, AList2: TThreadList<Integer>);
begin
  Inherited Create(false);
  fMySyncAddList1 := AsyncAddList1;
  fMySyncAddList2 := AsyncAddList2;
  fMyList1 := AList1;
  fMyList2 := AList2;    
end;

procedure TMyThread2.Execute;
var
  wr : TWaitResult;
  list : TList<Integer>;
  pulled : Boolean;
begin
  pulled := false;
  while (not Terminated) do
  begin
    if pulled then // Add a value to list2
    begin
      wr := fMySyncAddList2.WaitFor(0);
      if (wr <> wrSignaled) then
      begin
        fMyList2.Add(fAddVal);
        fMySyncAddList2.SetEvent; // Signal a new addition
        pulled := false;
      end
      else Sleep(100);
    end
    else begin // Wait for a new value in list1
      wr := fMySyncAddList1.WaitFor(INFINITE);
      if Terminated then
        Exit;
      if (wr = wrSignaled) then
      begin
        // Pull out the value
        list := fMyList1.LockList;
        try
          fAddVal := list.Last;
        finally
          fMyList1.UnlockList;
        end;
        // All clear
        pulled := true;
        fMySyncAddList1.ResetEvent;
        //ShowVal;
      end;
    end;
  end;
end;

{ TMyThread3 }

constructor TMyThread3.Create(ASyncAddList2: TSimpleEvent;
  AList2: TThreadList<Integer>);
begin
  Inherited Create(false);
  fMySyncAddList2 := AsyncAddList2;
  fMyList2 := AList2;
end;

procedure TMyThread3.Execute;
var
  wr : TWaitResult;
  list : TList<Integer>;
begin
  while not Terminated do
  begin
    wr := fMySyncAddList2.WaitFor(INFINITE);
    if Terminated then
      Exit;
    if (wr = wrSignaled)  then // Wait for signal
    begin
      // Pull out the value
      list := fMyList2.LockList;
      try
        fAddVal := list.Last;
        //ShowVal;
      finally
        fMyList2.UnlockList;
      end;
      // Clear event
      fMySyncAddList2.ResetEvent;
    end;
  end;
end;

var
  list1,list2 : TThreadList<Integer>;
  syncList1,syncList2 : TSimpleEvent;
  thread1 : TMyThread1;
  thread2 : TMyThread2;
  thread3 : TMyThread3;
begin
  list1 := TThreadList<Integer>.Create;
  list2 := TThreadList<Integer>.Create;
  syncList1 := TSimpleEvent.Create(Nil,True,False,'',false);
  syncList2 := TSimpleEvent.Create(Nil,True,False,'',false);
  thread3 := TMyThread3.Create(syncList2,list2);
  thread2 := TMyThread2.Create(syncList1,syncList2,list1,list2);
  thread1 := TMyThread1.Create(syncList1,list1);
  Try
    WriteLn('Press [Enter] key to stop.');
    ReadLn;

  Finally
    thread3.Terminate;
    syncList2.SetEvent; // Wake up call
    thread3.Free;
    thread2.Terminate;
    syncList1.SetEvent; // Wake up call
    thread2.Free;
    thread1.Free;
    syncList1.Free;
    syncList2.Free;
    list1.Free;
    list2.Free;
  End;
end.

添加了一个示例,其中两个TThreadedQueue在线程之间传输信息。线程保留整数的内部列表。正如@DavidHeffernan指出的那样,代码更加简单。

program Project63;

{$APPTYPE CONSOLE}

uses
  System.SysUtils,
  System.Classes,
  System.SyncObjs,
  System.Generics.Collections;

Type
  TMyThread1 = Class(TThread)
    private
      fMyList : TList<Integer>;
      fMyQueue : TThreadedQueue<Integer>;
      fAddVal : Integer;
    public
      Constructor Create(AQueue : TThreadedQueue<Integer>);
      procedure Execute; override;
  End;
  TMyThread2 = Class(TThread)
    private
      fMyList1,fMyList2 : TList<Integer>;
      fMyQueue1,fMyQueue2 : TThreadedQueue<Integer>;
      fAddVal : Integer;
    public
      Constructor Create(AQueue1,AQueue2: TThreadedQueue<Integer>);
      procedure Execute; override;
  End;
  TMyThread3 = Class(TThread)
    private
      fMyList : TList<Integer>;
      fMyQueue : TThreadedQueue<Integer>;
      fAddVal : Integer;
    public
      Constructor Create(AQueue : TThreadedQueue<Integer>);
      procedure Execute; override;
  End;

constructor TMyThread1.Create( AQueue : TThreadedQueue<Integer>);
begin
  Inherited Create(false);
  fMyQueue:= AQueue;
  fMyList := TList<Integer>.Create;
end;

procedure TMyThread1.Execute;
begin
  while (not Terminated) do
  begin
    Sleep(1000); // Simulate some work
    fAddVal := Random(100);
    fMyList.Add(fAddVal);
    fMyQueue.PushItem(fAddVal); // Signal a new addition
  end;
  fMyList.Free;
end;

constructor TMyThread2.Create(AQueue1,AQueue2: TThreadedQueue<Integer>);
begin
  Inherited Create(false);
  fMyQueue1 := AQueue1;
  fMyQueue2 := AQueue2;
  fMyList1 := TList<Integer>.Create;
  fMyList2 := TList<Integer>.Create;
end;

procedure TMyThread2.Execute;
var
  queueSize : Integer;
begin
  while (not Terminated) do
  begin
    if (fMyQueue1.PopItem(queueSize,fAddVal) = wrSignaled) and 
       (not Terminated) then
    begin
      fMyList1.Add(fAddVal);
      // Do some work and send a new value to next thread
      fMyQueue2.PushItem(fAddVal);
      fMyList2.Add(fAddVal);
      
    end;
  end;
  fMyList1.Free;
  fMyList2.Free;
end;

constructor TMyThread3.Create(AQueue : TThreadedQueue<Integer>);
begin
  Inherited Create(false);
  fMyQueue := AQueue;
  fMyList := TList<Integer>.Create;
end;

procedure TMyThread3.Execute;
var
  queueSize : Integer;
begin
  while not Terminated do
  begin
    if (fMyQueue.PopItem(queueSize,fAddVal) = wrSignaled) and 
       (not Terminated) then
    begin
      fMyList.Add(fAddVal);
      // Do some work on list
      
    end;
  end;
  fMyList.Free;
end;

var
  queue1,queue2 : TThreadedQueue<Integer>;
  thread1 : TMyThread1;
  thread2 : TMyThread2;
  thread3 : TMyThread3;
begin
  queue1 := TThreadedQueue<Integer>.Create;
  queue2 := TThreadedQueue<Integer>.Create;
  thread3 := TMyThread3.Create(queue2);
  thread2 := TMyThread2.Create(queue1,queue2);
  thread1 := TMyThread1.Create(queue1);
  Try
    WriteLn('Press [Enter] key to stop.');
    ReadLn;

  Finally
    thread3.Terminate;
    queue2.PushItem(0); // Wake up call
    thread3.Free;
    thread2.Terminate;
    queue1.PushItem(0); // Wake up call
    thread2.Free;
    thread1.Free;
    queue1.Free;
    queue2.Free;
  End;
end.

答案 1 :(得分:1)

首先想到的是信号量。信号量是一个同步原语,里面有一个计数器:一个线程试图递减计数器,如果它为零,则线程阻塞(即没有调度并且不吃CPU,只是无害地等待)。另一个线程递增计数器,导致阻塞的线程继续。

每个列表可能都有一个信号量,因此消费线程在读取之前递减信号量,生成器线程在写入后递增它。

还有另一件事需要注意:是否允许一个线程从列表中获取数据而另一个线程正在修改它?这取决于如何实现列表(或一般的集合),因此请尝试在文档中查找列表的“线程安全”。也许你需要另一个同步的原则:互斥。互斥锁被“占用”然后由线程“释放”,当多个线程试图锁定互斥锁时,其中一个必须等​​待。每个列表中有一个互斥锁,并且使用此互斥锁进行修改和读取,这里可能是合适的。