[mark4o]

POSIX does not require EOF to be returned from a blocking read() if the same file descriptor is passed to close() in another thread. Even if it appears to work on some particular OS, consider the case where the reading thread may have called read() but is preempted just before entering the kernel. If another thread then closes the file descriptor, expecting the first thread to see EBADF or EOF, but then the file descriptor is reused (e.g. by accept()) before the first thread resumes, the reading thread may block reading from an unrelated socket. Even if you can guarantee that accept(), open(), or other calls that explicitly allocate a file descriptor will not be called, ordinary library functions are generally allowed to use file descriptors internally (e.g. to read a configuration file), so closing the file descriptor while another thread is reading from it is almost certainly a bug.