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52 lines
2.5 KiB
Groff
52 lines
2.5 KiB
Groff
.TH iopause 3
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.SH NAME
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iopause \-
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.SH SYNTAX
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.B #include <libowfat/iopause.h>
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int \fBiopause\fP(iopause_fd** \fIx\fR,unsigned int \fIlen\fR,
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struct taia \fIdeadline\fR,struct taia \fIstamp\fR);
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.SH DESCRIPTION
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iopause checks for file descriptor readability or writability as specified
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by \fIx\fR[0].fd, \fIx\fR[0].events, \fIx\fR[1].fd, \fIx\fR[1].events, ..., \fIx\fR[\fIlen\fR-1].fd,
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\fIx\fR[\fIlen\fR-1].events. If \fIx\fR[i].events includes the bit IOPAUSE_READ, iopause
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checks for readability of the descriptor \fIx\fR[i].fd; if \fIx\fR[i].events includes
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the bit IOPAUSE_WRITE, iopause checks for writability of the descriptor
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\fIx\fR[i].fd; other bits in \fIx\fR[i].events have undefined effects.
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iopause sets the IOPAUSE_READ bit in \fIx\fR[i].revents if it finds that \fIx\fR[i].fd
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is readable, and it sets the IOPAUSE_WRITE bit in \fIx\fR[i].revents if it finds
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that \fIx\fR[i].fd is writable. Beware that readability and writability may be
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destroyed at any moment by other processes with access to the same ofile
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that \fIx\fR[i].fd refers to.
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If there is no readability or writability to report, iopause waits until
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\fIdeadline\fR for something to happen. iopause will return before \fIdeadline\fR if a
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descriptor becomes readable or writable, or an interrupting signal
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arrives, or some system-defined amount of time passes. iopause sets
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revents in any case.
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You must put a current timestamp into \fIstamp\fR before calling iopause.
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.SH "IMPLEMENTATION NOTES"
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The current implementation of iopause uses the \fBpoll\fR function if that is
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available. On some systems, \fBpoll\fR needs to dynamically allocate kernel
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memory; when not much memory is available, iopause will return
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immediately, and will report (often incorrectly) that no descriptors are
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readable or writable. This is a kernel bug, and I encourage vendors to fix
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it.
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If \fBpoll\fR is not available, iopause uses the \fBselect\fR function. This function
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cannot see descriptor numbers past a system-defined limit, typically 256
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or 1024; iopause will artificially pretend that those descriptors are
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never readable or writable.
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Future implementations of iopause may work around these problems on some
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systems, at the expense of chewing up all available CPU time.
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Both \fBpoll\fR and \fBselect\fR use relative timeouts rather than absolute deadlines.
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Some kernels round the timeout down to a multiple of 10 milliseconds; this
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can burn quite a bit of CPU time as the deadline approaches. iopause
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compensates for this by adding 20 milliseconds to the timeout.
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.SH "SEE ALSO"
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select(2), poll(3), taia_now(3)
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