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40 lines
1.6 KiB
Groff
40 lines
1.6 KiB
Groff
.TH io_wait 3
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.SH NAME
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io_wait \- wait for events
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.SH SYNTAX
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.B #include <io.h>
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void \fBio_wait\fP();
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.SH DESCRIPTION
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io_wait() checks the descriptors that the program is interested in to
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see whether any of them are ready. If none of them are ready, io_wait()
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tries to pause until one of them is ready, so that it does not take time
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away from other programs running on the same computer.
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io_wait pays attention to timeouts: if a descriptor reaches its timeout,
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and the program is interested in reading or writing that descriptor,
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io_wait will return promptly.
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Under some circumstances, io_wait will return even though no interesting
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descriptors are ready. Do not assume that a descriptor is ready merely
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because io_wait has returned.
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io_wait is not interrupted by the delivery of a signal. Programs that
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expect interruption are unreliable: they will block if the same signal
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is delivered a moment before io_wait. The correct way to handle signals
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is with the self-pipe trick.
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.SH NOTE
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Depending on the underlying operating system primitive, there is a
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potential race condition to be aware of. Some event notification
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mechanisms (for example, kqueue on BSD and epoll on Linux) will return
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multiple events. If your application operates on pairs of file
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descriptors (a proxy server maybe), and an error on one descriptor
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can lead to closing the other descriptor, then an outstanding event on
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the other descriptor can still be queued for delivery to you. Be
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prepared to receive events for a descriptor that has already been
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closed.
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.SH "SEE ALSO"
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io_waituntil(3), io_check(3), io_wantread(3), io_wantwrite(3), io_fd(3)
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