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.TH io_nonblock 3
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.SH NAME
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io_nonblock \- switch to non-blocking I/O
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.SH SYNTAX
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.B #include <libowfat/io.h>
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void \fBio_nonblock\fP(int64 fd);
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.SH DESCRIPTION
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io_nonblock puts UNIX descriptor fd into ``non-blocking mode.'' Calling
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io_nonblock(\fIfd\fR) before io_fd(\fIfd\fR) makes io_tryread and
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io_trywrite faster and more efficient.
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Actually, current UNIX kernels do not support non-blocking descriptors; they
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support non-blocking open files. Furthermore, many programs will break if they
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encounter non-blocking mode. This means that you must not use io_nonblock for a
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descriptor inherited from another program.
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io_nonblock has no return value; it always succeeds. If d is not the number of
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a UNIX descriptor, io_nonblock has no effect.
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If io_fd is given a descriptor in blocking mode, io_tryread and io_trywrite go
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through the following contortions to avoid blocking:
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.RS 0
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.nr step 1 1
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.IP \n[step] 3
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Stop if poll says that the descriptor is not ready. Otherwise there's a good
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chance, but not a guarantee: even if poll says the descriptor is ready, the
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descriptor might not be ready a moment later. (Furthermore, poll can fail on
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some systems.)
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.IP \n+[step]
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Catch SIGALRM. SIGALRM must not be blocked, and must not be used elsewhere in
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the program.
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.IP \n+[step]
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Set an interval timer so that any blocking call will be interrupted by SIGALRM
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within 10 milliseconds. (Current UNIX kernels do not allow any shorter
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interval.) Of course, this may still mean a 10-millisecond delay.
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.RE
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If io_fd is given a descriptor in non-blocking mode (or a descriptor for a
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regular disk file), io_tryread and io_trywrite avoid these contortions.
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.SH "SEE ALSO"
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io_wait(3), io_canwrite(3)
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