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iopause(3)            DragonFly Library Functions Manual            iopause(3)


NAME

       iopause -


SYNTAX

       #include <iopause.h>

       int iopause(iopause_fd** x,unsigned int len,
                   struct taia deadline,struct taia stamp);


DESCRIPTION

       iopause checks for file descriptor readability or writability as
       specified by x[0].fd, x[0].events, x[1].fd, x[1].events, ...,
       x[len-1].fd, x[len-1].events. If x[i].events includes the bit
       IOPAUSE_READ, iopause checks for readability of the descriptor x[i].fd;
       if x[i].events includes the bit IOPAUSE_WRITE, iopause checks for
       writability of the descriptor x[i].fd; other bits in x[i].events have
       undefined effects.

       iopause sets the IOPAUSE_READ bit in x[i].revents if it finds that
       x[i].fd is readable, and it sets the IOPAUSE_WRITE bit in x[i].revents
       if it finds that x[i].fd is writable. Beware that readability and
       writability may be destroyed at any moment by other processes with
       access to the same ofile that x[i].fd refers to.

       If there is no readability or writability to report, iopause waits
       until deadline for something to happen. iopause will return before
       deadline if a descriptor becomes readable or writable, or an
       interrupting signal arrives, or some system-defined amount of time
       passes. iopause sets revents in any case.

       You must put a current timestamp into stamp before calling iopause.


IMPLEMENTATION NOTES

       The current implementation of iopause uses the poll function if that is
       available. On some systems, poll needs to dynamically allocate kernel
       memory; when not much memory is available, iopause will return
       immediately, and will report (often incorrectly) that no descriptors
       are readable or writable. This is a kernel bug, and I encourage vendors
       to fix it.

       If poll is not available, iopause uses the select function. This
       function cannot see descriptor numbers past a system-defined limit,
       typically 256 or 1024; iopause will artificially pretend that those
       descriptors are never readable or writable.

       Future implementations of iopause may work around these problems on
       some systems, at the expense of chewing up all available CPU time.

       Both poll and select use relative timeouts rather than absolute
       deadlines.  Some kernels round the timeout down to a multiple of 10
       milliseconds; this can burn quite a bit of CPU time as the deadline
       approaches. iopause compensates for this by adding 20 milliseconds to
       the timeout.


SEE ALSO

       select(2), poll(3), taia_now(3)

                                                                    iopause(3)

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