Peek through recently network's code, the new IORef CInt based Socket seems to still have previous discussed fd-reuse race condiftion:

1. Thread A acquires a Socket 's fd by fdSocket, when it's about to do some operations, the scheduler decide to pause thread A.

2. Thread B close the socket, rewrite the Socket 's IORef 's content.

3. Thread C open a new socket, unfortunately got the same fd number thread A is holding now.

4. When thread A is resumed, it's unaware of thread B and thread C 's behavior, thus the following operations will performed successfully, but on a wrong fd.

Maybe it's necessary to add some docs on close ?