Socket Descriptor closed from another thread on certain condition when accept() call on the same socket is going on in Linux?

Question

1 thread is making an accept call in for(;;;) loop .On a certain condition closeSocket is called and it closes the same socket on which accept call is being made . The accept call gives error . I get EBDAF error on Solaris and EINVAL error on Linux . How should i overcome this problem . Can I check the socketnum state before making an accept call . How should I approach this problem .

Answer 1

You cannot close a socket in one thread while another thread is using it. The basic problem is that there is simply no way to know whether the other thread is using the socket or about to use the socket. And if it's about to use the socket, there are unavoidable race conditions. This mistake has caused real world problems, including one with serious security implications.

Instead, just don't close the socket. Signal the thread that might be using the socket any other way, and then have that thread close the socket.

Answer 2

accept will return with error because the socket (file descriptor) was closed. You can consider this error in your code.

An alternative technique for not getting error that is common in many applications (Thrift uses it): from a second thread you connect to this socket and send a special message, for example, just "1". When the server receives this message it finishes the loop and closes the socket.

Of course there is a risk of DoS attack if another machine begins to send "1" to your server. Then you need to check the message comes from the same machine and from a port used by your process. Or better, do what Martin James says below.