Cygwin: Fix racy read to detect applications sockets close

Cygwin: Fix racy read to detect applications sockets close

The mechanism to detect the applications sockets close is racy and
could potentially discard data. A read(3) is performed on the application
socket and the returned len is compared to 0 to detect the case where an
application closed the socket. If a read(3) occur in the thread_manage_apps
*before* the consumption of the data in the consumer, one byte of data would
be discarded.

To fix this race, perform a recv(3) on the socket with the MSG_PEEK flag.
This has no impact on the data delivery to the consumer and can successfully
detect the applications sockets close.