Fselect(2)                Oct. 1, 1991                 Fselect(2)



NAME
     Fselect - select file descriptors that are ready for reading
     or writing

SYNOPSIS
     WORD Fselect(WORD timeout, LONG *rfds, LONG *wfds, ((long)0));

DESCRIPTION
     Fselect checks two sets of open file descriptors and  deter-
     mines  which have data ready to read, and/or which are ready
     to be written to. If none are ready yet, the process goes to
     sleep  until  some  member  of the sets are ready or until a
     specified amount of time has elapsed.

     rfds points to a long word which represents a set of  GEMDOS
     file  descriptors;  bit  n  of this long word is set if file
     descriptor n is to be checked for input data. An  empty  set
     may optionally be represented by a NULL pointer instead of a
     pointer to 0. Similarly, wfds points to a 32 bit  long  word
     which indicates which file descriptors are to be checked for
     output status. When Fselect returns, the old values  pointed
     to  by  rfds  and  wfds (if non-NULL) are overwritten by new
     long words indicating which file  descriptors  are  actually
     ready for reading or writing; these will always form subsets
     of the file descriptors originally  specified  as  being  of
     interest.

     timeout is a 16 bit unsigned integer  specifying  a  maximum
     number  of  milliseconds  to  wait before returning; if this
     number is 0, no maximum is set and the call will block until
     one  of  the file descriptors specified is ready for reading
     or writing, as appropriate. Thus,  Fselect(0,0L,0L,0L)  will
     block  forever, whereas Fselect(1,0L,0L,0L) will pause for 1
     millisecond.

     The final argument, a long word, must always  be  0  (it  is
     reserved for future enhancements).

RETURNS
     The sum of the numbers of bits set in the long words pointed
     to  by rfds and wfds.  This will be 0 if the timeout expires
     without any of the specified file descriptors becoming ready
     for  reading  or writing, as appropriate, and nonzero other-
     wise.

     EIHNDL if any handle specified by the long words pointed  to
     by rfds or wfds is not a valid (open) GEMDOS handle.

SEE ALSO
     Finstat(2), Foutstat(2)





Version 0.9   Last change: MiNT Programmer's Manual             1






Fselect(2)                Oct. 1, 1991                 Fselect(2)



BUGS
     The system timer is not actually  accurate  to  the  nearest
     millisecond,  so  the  timeout  could last for up to 19 mil-
     liseconds longer than specified.

     Fselect does not work correctly on any  BIOS  device  except
     the keyboard.

     Note that if an error condition occurs on one  of  the  file
     descriptors  (for example, if the read status of a pipe with
     no more writers is being requested) then Fselect  will  mark
     that file descriptor as being ready for reading (or writing,
     as appropriate). This is not strictly speaking a bug,  since
     a  subsequent  read  will not block (it will return an error
     condition), but programmers should be aware of the possibil-
     ity.







































Version 0.9   Last change: MiNT Programmer's Manual             2