io_wait(3)

NAME
io_wait - wait for events

SYNTAX
#include <libowfat/io.h>

void io_wait();

DESCRIPTION
io_wait() checks the descriptors that the program is interested in to see whether any of them are ready. If none of them are ready, io_wait() tries to pause until one of them is ready, so that it does not take time away from other programs running on the same computer.

io_wait pays attention to timeouts: if a descriptor reaches its timeout, and the program is interested in reading or writing that descriptor, io_wait will return promptly.

Under some circumstances, io_wait will return even though no interesting descriptors are ready. Do not assume that a descriptor is ready merely because io_wait has returned.

io_wait is not interrupted by the delivery of a signal. Programs that expect interruption are unreliable: they will block if the same signal is delivered a moment before io_wait. The correct way to handle signals is with the self-pipe trick.

NOTE
Depending on the underlying operating system primitive, there is a potential race condition to be aware of. Some event notification mechanisms (for example, kqueue on BSD and epoll on Linux) will return multiple events. If your application operates on pairs of file descriptors (a proxy server maybe), and an error on one descriptor can lead to closing the other descriptor, then an outstanding event on the other descriptor can still be queued for delivery to you. Be prepared to receive events for a descriptor that has already been closed.

SEE ALSO
io_waituntil(3), io_check(3), io_wantread(3), io_wantwrite(3), io_fd(3)