io_nonblock - switch to non-blocking I/O
void io_nonblock(int64 fd);
io_nonblock puts UNIX descriptor fd into ``non-blocking mode.'' Calling
io_nonblock(fd) before io_fd(fd) makes io_tryread and io_trywrite
faster and more efficient.
Actually, current UNIX kernels do not support non-blocking descriptors;
they support non-blocking open files. Furthermore, many programs will
break if they encounter non-blocking mode. This means that you must not
use io_nonblock for a descriptor inherited from another program.
io_nonblock has no return value; it always succeeds. If d is not the
number of a UNIX descriptor, io_nonblock has no effect.
If io_fd is given a descriptor in blocking mode, io_tryread and
io_trywrite go through the following contortions to avoid blocking:
1 Stop if poll says that the descriptor is not ready. Otherwise
there's a good chance, but not a guarantee: even if poll says the
descriptor is ready, the descriptor might not be ready a moment
later. (Furthermore, poll can fail on some systems.)
2 Catch SIGALRM. SIGALRM must not be blocked, and must not be used
elsewhere in the program.
3 Set an interval timer so that any blocking call will be interrupted
by SIGALRM within 10 milliseconds. (Current UNIX kernels do not
allow any shorter interval.) Of course, this may still mean a
If io_fd is given a descriptor in non-blocking mode (or a descriptor
for a regular disk file), io_tryread and io_trywrite avoid these