Question

Using a .NET TcpClient if I have called an asynchronous BeginRead() on the associated network stream can I still call Write() on that stream on another thread?

Or do I have to lock() the TcpClient in the code that is called back from the BeginRead and the code that does the send?

Also if I close the TcpClient with:

client.GetStream().Close();
client.Close();

Do I have to lock() on the TcpClient as well?

Answer 1

The read/write portions of the TcpClient are thread safe, as explained in the documentation for the NetworkStream class (which is what the TcpClient uses for its actual IO):

Read and write operations can be
performed simultaneously on an
instance of the NetworkStream class
without the need for synchronization.
As long as there is one unique thread
for the write operations and one
unique thread for the read operations,
there will be no cross-interference
between read and write threads and no
synchronization is required.

To do with the closing, if you close the TcpClient on one thread, but then try to read/write using it on another thread after it is closed, an exception will be thrown. You can either synchronise the threads before it is closed in order to prevent them using the TcpClient, or just catch and handle the exception (for example, you might exit the thread’s executing loop).