AutoResetEvent.WaitOne(int,bool)的线程同步问题

yhwebus 2004-03-18 01:27:35

我想知道第二个参数究竟做什么控制的，看了下面的介绍,还是不清楚,有人能帮忙解释下吗?

WaitHandle.WaitOne Method (Int32, Boolean)
When overridden in a derived class, blocks the current thread until the current WaitHandle receives a signal, using 32-bit signed integer to measure the time interval and specifying whether to exit the synchronization domain before the wait.

[C#]
public virtual bool WaitOne(
int millisecondsTimeout,
bool exitContext)

Parameters----
millisecondsTimeout :
The number of milliseconds to wait, or Timeout.Infinite (-1) to wait indefinitely.

exitContext :
true to exit the synchronization domain for the context before the wait (if in a synchronized context), and reacquire it; otherwise, false.

Return Value-----
true if the current instance receives a signal; otherwise, false.

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MuseIn 2004-09-08

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本程序，实现一个简单的语音聊天功能，将麦克风采集到的音频数据经G711压缩后，通过UDP协议传输。在本文中不讨论如何通过麦克风采集音频数据，也不讨论G711压缩的细节，相关内容可以查看文章后参考文献的内容。系统架构如下所示： | Invite | | --------------------------------> | | OK | | <-------------------------------- | | | | --------------------------------> | | Audio flow | | <-------------------------------- | | Bye | | --------------------------------> | A B 系统所用到的命令如：Invite、OK、Bye等设计为一个枚举类型变量， enum Command { Invite, //Make a call. Bye, //End a call. Busy, //User busy. OK, //Response to an invite message. OK is sent to //indicate that call is accepted. Null, //No command. } 当用户想要语音聊天时，发送Invite消息，等待对方的反馈OK应答。当收到OK应答后，开始发送/接受语音信息。如果对方拒绝聊天，则发送Busy信息作为应答。要终止聊天时，发送Bye消息即可。程序在端口1450同步实现连接建立消息的收发，在端口1550异步收发聊天信息。也就是说，本程序监听两个端口，一个负责呼叫消息，另一个负责音频数据。监听1450端口的代码： //使用UDP clientSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp); EndPoint ourEP = new IPEndPoint(IPAddress.Any, 1450); //Listen asynchronously on port 1450 for //coming messages (Invite, Bye, etc). clientSocket.Bind(ourEP); //Receive data from any IP. EndPoint remoteEP = (EndPoint)(new IPEndPoint(IPAddress.Any, 0)); byteData = new byte[1024]; //Receive data asynchornously. clientSocket.BeginReceiveFrom(byteData, 0, byteData.Length, SocketFlags.None, ref remoteEP, new AsyncCallback(OnReceive), null); 当收到发送来的消息后，根据消息类型来进行对应的处理。 private void OnReceive(IAsyncResult ar) { try { EndPoint receivedFromEP = new IPEndPoint(IPAddress.Any, 0); //Get the IP from where we got a message. clientSocket.EndReceiveFrom(ar, ref receivedFromEP); //Convert the bytes received into an object of type Data. Data msgReceived = new Data(byteData); //Act according to the received message. switch (msgReceived.cmdCommand) { //We have an incoming call. case Command.Invite: { if (bIsCallActive == false) { //We have no active call. //Ask the user to accept the call or not. if (MessageBox.Show("Call coming from " + msgReceived.strName + ".\r\n\r\nAccept it?", "VoiceChat", MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes) { SendMessage(Command.OK, receivedFromEP); vocoder = msgReceived.vocoder; otherPartyEP = receivedFromEP; otherPartyIP = (IPEndPoint)receivedFromEP; InitializeCall(); } else { //The call is declined. Send a busy response. SendMessage(Command.Busy, receivedFromEP); } } else { //We already have an existing call. Send a busy response. SendMessage(Command.Busy, receivedFromEP); } break; } //OK is received in response to an Invite. case Command.OK: { //Start a call. InitializeCall(); break; } //Remote party is busy. case Command.Busy: { MessageBox.Show("User busy.", "VoiceChat", MessageBoxButtons.OK, MessageBoxIcon.Exclamation); break; } case Command.Bye: { //Check if the Bye command has indeed come from the user/IP with which we have //a call established. This is used to prevent other users from sending a Bye, which //would otherwise end the call. if (receivedFromEP.Equals (otherPartyEP) == true) { //End the call. UninitializeCall(); } break; } } byteData = new byte[1024]; //Get ready to receive more commands. clientSocket.BeginReceiveFrom(byteData, 0, byteData.Length, SocketFlags.None, ref receivedFromEP, new AsyncCallback (OnReceive), null); } catch (Exception ex) { MessageBox.Show(ex.Message, "VoiceChat-OnReceive ()", MessageBoxButtons.OK, MessageBoxIcon.Error); } } 为了保证在收发音频数据时，不产生UI阻塞，采用多线程来异步收发数据。 private void InitializeCall() { try { //Start listening on port 1500. udpClient = new UdpClient(1550); Thread senderThread = new Thread(new ThreadStart(Send)); Thread receiverThread = new Thread(new ThreadStart(Receive)); bIsCallActive = true; //Start the receiver and sender thread. receiverThread.Start(); senderThread.Start(); btnCall.Enabled = false; btnEndCall.Enabled = true; } catch (Exception ex) { MessageBox.Show(ex.Message, "VoiceChat-InitializeCall ()", MessageBoxButtons.OK, MessageBoxIcon.Error); } } 异步发送从麦克风采集到的音频数据 * Send synchronously sends data captured from microphone across the network on port 1550. */ private void Send() { try { //The following lines get audio from microphone and then send them //across network. captureBuffer = new CaptureBuffer(captureBufferDescription, capture); CreateNotifyPositions(); int halfBuffer = bufferSize / 2; captureBuffer.Start(true); bool readFirstBufferPart = true; int offset = 0; MemoryStream memStream = new MemoryStream(halfBuffer); bStop = false; while (!bStop) { autoResetEvent.WaitOne(); memStream.Seek(0, SeekOrigin.Begin); captureBuffer.Read(offset, memStream, halfBuffer, LockFlag.None); readFirstBufferPart = !readFirstBufferPart; offset = readFirstBufferPart ? 0 : halfBuffer; //TODO: Fix this ugly way of initializing differently. //Choose the vocoder. And then send the data to other party at port 1550. if (vocoder == Vocoder.ALaw) { byte[] dataToWrite = ALawEncoder.ALawEncode(memStream.GetBuffer()); udpClient.Send(dataToWrite, dataToWrite.Length, otherPartyIP.Address.ToString (), 1550); } else if (vocoder == Vocoder.uLaw) { byte[] dataToWrite = MuLawEncoder.MuLawEncode(memStream.GetBuffer()); udpClient.Send(dataToWrite, dataToWrite.Length, otherPartyIP.Address.ToString(), 1550); } else { byte[] dataToWrite = memStream.GetBuffer(); udpClient.Send(dataToWrite, dataToWrite.Length, otherPartyIP.Address.ToString(), 1550); } } } catch (Exception ex) { MessageBox.Show(ex.Message, "VoiceChat-Send ()", MessageBoxButtons.OK, MessageBoxIcon.Error); } finally { captureBuffer.Stop(); //Increment flag by one. nUdpClientFlag += 1; //When flag is two then it means we have got out of loops in Send and Receive. while (nUdpClientFlag != 2) { } //Clear the flag. nUdpClientFlag = 0; //Close the socket. udpClient.Close(); } } 从端口1550处接受收到的音频数据 private void Receive() { try { bStop = false; IPEndPoint remoteEP = new IPEndPoint(IPAddress.Any, 0); while (!bStop) { //Receive data. byte[] byteData = udpClient.Receive(ref remoteEP); //G711 compresses the data by 50%, so we allocate a buffer of double //the size to store the decompressed data. byte[] byteDecodedData = new byte[byteData.Length * 2]; //Decompress data using the proper vocoder. if (vocoder == Vocoder.ALaw) { ALawDecoder.ALawDecode(byteData, out byteDecodedData); } else if (vocoder == Vocoder.uLaw) { MuLawDecoder.MuLawDecode(byteData, out byteDecodedData); } else { byteDecodedData = new byte[byteData.Length]; byteDecodedData = byteData; } //Play the data received to the user. playbackBuffer = new SecondaryBuffer(playbackBufferDescription, devi

线程同步的其他方式： 1、AutoResetEvent 使用WaitOne和set 进行阻塞和释放阻塞的线程， WaitOne方法定义： public virtual bool WaitOne(int millisecondsTimeout）;该方法用来阻塞线程，当在指定的时间间隔还没有收到一个信号时，将返回false。 public AutoResetEvent(bool initia...

WaitHandle.WaitOne 方法 () .NET Framework 2.0 其他版本 .NET Framework (current version) .NET Framework 4 Silverlight .NET Framework 3.5 .NET Framework 3.0 当在派生类中重写时，阻塞当

AutoResetEvent a1 = new AutoResetEvent(false); 不传入false默认为true，不会阻塞线程，所以必须传false。 WaitOne(int)； WaitOne(int,bool)； WaitOne(timespan,bool)；第二个参数传true代表超时后由set()设置不阻塞线程，如果传入false，如:WaitOne(2000,false);当超过两秒后线程就解除阻塞了，也就是等第二次在进入此线程时候会直接执行并不会阻塞线程。参考链接：ht.

最近捣鼓了一下多线程的同步问题，发现其实C#关于多线程同步事件处理还是很灵活，这里主要写一下，自己测试的一些代码，涉及到了AutoResetEvent 和 ManualResetEvent，当然还有也简要提了一下System.Threading.WaitHandle.WaitOne 、System.Threading.WaitHandle.WaitAny和System.Threading.Wait

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