@ 所有人：
CompletionPortThreads
This kind of thread is used for I/O operations, whenever is possible. Windows NT, Windows 2000, and Windows XP offer an object specialized on asynchronous operations, called IOCompletionPort. With the API associated with this object we can launch asynchronous I/O operations managed with a thread pool by the system, in an efficient way and with few resources. However, Windows 95, Windows 98, and Windows Me have some limitations with asynchronous I/O operations. For example, IOCompletionPorts functionality is not offered and asynchronous operations on some devices, such as disks and mail slots, cannot be performed. Here you can see one of the greatest features of the .NET Framework: compile once and execute on multiple systems. Depending on the target platform, the .NET Framework will decide to use the IOCompletionPorts API or not, maximizing the performance and minimizing the resources.
If you run this program on Microsoft Windows NT, Windows 2000, or Windows XP, you will see the following output:
Connected to localhost:80
WorkerThreads: 24, CompletionPortThreads: 25
Request sent to localhost:80
WorkerThreads: 25, CompletionPortThreads: 24
As you can see, connecting with a socket uses a worker thread, while sending the data uses a CompletionPort. This following sequence is followed:
- We get the local IP address and connect to it asynchronously.
- Socket performs the asynchronous connection on a worker thread, since Windows IOCompletionPorts cannot be used to establish connections on sockets.
- Once the connection is established, the Socket class calls the specified function ConnectCallback. This callback shows the number of available threads on the pool, this way we can see that it is being executed on a worker thread.
- An asynchronous request is sent from the same function ConnectCallback. We use for this the BeginSend method, after encoding the Get / request in ASCII code.
- Send/receive operations on a socket can be performed asynchronously with an IOCompletionPort, so when our request is done, the callback function SendCallback is executed on a CompletionPortthread. We can check this because the function itself shows the number of available threads and we can see that only those corresponding to CompletionPorts have been decreased.
If we run the same code on a Windows 95, Windows 98, or Windows Me platform, the result will be the same on the connection, but the request will be sent on a worker thread, instead of a CompletionPort. The important thing you should learn about this is that the Socket class always uses the best available mechanism, so you can develop your application without taking into account the target platform.
各位，可以盖棺定论了吗？