Mark fd as ignored so that the next call to wait will yield the same result
for fd as last time.
This function must be called if no operation (read/write/recv/send/etc.) will be performed on fd before the next call to
wait.
The reason why this is needed is because the underlying implementation might not allow querying the fd more than once between calls to one of the re-enabling operations.
| this |
a file descriptor set. |
| fd |
a file descriptor. |