poll man page on HP-UX

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poll(2)								       poll(2)

       poll - monitor I/O conditions on multiple file descriptors

       provides	 a  general  mechanism for reporting I/O conditions associated
       with a set of file descriptors and for waiting until one or more speci‐
       fied conditions becomes true.  Specified conditions include the ability
       to read or write data without blocking, and error conditions.

	      fds	     Points to an array of structures,	one  for  each
			     file descriptor of interest.

	      nfds	     Specifies	the  number  of	 structures in the fds

	      timeout	     Specifies the maximum length  of  time  (in  mil‐
			     liseconds) to wait for at least one of the speci‐
			     fied conditions to occur.

       Each structure includes the following members:

	      File descriptor
	      Requested conditions
	      Reported conditions

       The member of each structure specifies an open  file  descriptor.   The
       function	 uses  the  member  to determine what conditions to report for
       this file descriptor.  If one or more of these conditions is true, sets
       the associated member.

       ignores	any  structure whose member is negative.  If the member of all
       structures is negative, returns 0 and has no other results.

       The and members of the structure are bit masks.	 The  calling  process
       sets  the  bit  mask,  and sets the bit masks.  These bit masks contain
       ORed combinations of condition flags.  The  following  condition	 flags
       are defined:

	      Data can be read without blocking.
				  For  streams, this flag means that a message
				  that is not high priority is at the front of
				  the  stream  head  read queue.  This message
				  can be of zero length.

	      Synonym for

	      A high priority message is available.
				  For streams, this message  can  be  of  zero

	      Data can be written without blocking.
				  For streams, this flag specifies that normal
				  data (not high priority or priority  band  >
				  0)  can  be written without being blocked by
				  flow control.	 This flag  is	not  used  for
				  high	priority data, because it can be writ‐
				  ten even if the stream is flow controlled.

	      An error has occurred on the file descriptor.

	      The device has been disconnected.
				  For streams, this flag in is mutually exclu‐
				  sive	with  since a stream cannot be written
				  to after a hangup occurs.  This flag and and
				  are not mutually exclusive.

	      is not a valid file descriptor.

	      A non-priority message is available.
				  For  streams,	 this flag means that a normal
				  message (not high priority or priority  band
				  > 0) is at the front of the stream head read
				  queue.  This message can be of zero length.

	      A priority message (priority band > 0)
				  is at the front  of  the  stream  head  read
				  queue.   This	 message  can  be read without
				  blocking.   The  message  can	 be  of	  zero

	      Same as

	      Priority data (priority band > 0)
				  can be written without being blocked by flow
				  control.  Only previously written bands  are

	      A			  or  message specifying has reached the front
				  of the stream head read queue.

       The conditions indicated by and are true if and only if	at  least  one
       byte of data can be read or written without blocking.  The exception is
       regular files, which always poll true for and Also, streams  return  in
       even if the available message is of zero length.

       The  condition flags and are always set in if the conditions they indi‐
       cate are true for the specified file descriptor, whether or  not	 these
       flags are set in

       For  each  call	to  the	 set  of  reportable  conditions for each file
       descriptor consists of  those  conditions  that	are  always  reported,
       together	 with any further conditions for which flags are set in If any
       reportable condition is true for	 any  file  descriptor,	 returns  with
       flags set in for each true condition for that file descriptor.

       If  no  reportable  condition  is true for any of the file descriptors,
       waits up to timeout milliseconds for a reportable condition  to	become
       true.   If,  in that time interval, a reportable condition becomes true
       for any of the file descriptors, reports	 the  condition	 in  the  file
       descriptor's associated member and returns.  If no reportable condition
       becomes true, returns without setting any bit masks.

       If the timeout parameter is a value of −1, does	not  return  until  at
       least  one  specified  event has occurred.  If the value of the timeout
       parameter is 0, does not wait for an event to occur but returns immedi‐
       ately, even if no specified event has occurred.	The behavior of is not
       affected by whether the flag is	set  on	 any  of  the  specified  file

       Upon  successful	 completion, returns a nonnegative value.  If the call
       returns 0, has timed out and has not set any of the bit masks.  A posi‐
       tive  value  indicates the number of file descriptors for which has set
       the bit mask.  If fails, it returns −1 and sets to indicate the error.

       fails if any of the following conditions are encountered:

	      Allocation of internal data structures failed.
			     A later call to may complete successfully.

	      A signal was delivered
			     before  any  of  the  selected   for   conditions
			     occurred or before the time limit expired.

	      One of the following conditions is true:

			     ·	timeout is a negative number other than −1.

			     ·	The nfds argument is less than 0, greater than
				or greater than or equal to The kernel parame‐
				ter  specifies	the  maximum  number  of  file
				descriptors  per  process  (see	 maxfiles(5)).
				specifies   the	 maximum  number  of  files  a
				process can have open at one time;  it	has  a
				value  of  2048	 if  the  resource limit for a
				process is less than or equal to 2048.

			     ·	One of the specified file descriptor refers to
				a stream or mux that is linked downstream from
				a mux.

	      The	     fds parameter in conjunction with the nfds param‐
			     eter  addresses  a	 location outside of the allo‐
			     cated address space  of  the  process.   Reliable
			     detection	of this error is implementation-depen‐

       Wait for input on file descriptor 0:

       Wait for input on and output on giving up after 10 seconds:

       Check for input or output on file descriptor 5 without waiting:

       Wait 3.5 seconds:

       Wait for a high priority, priority, or normal message on	 streams  file
       descriptor 0:

       read(2), write(2), select(2), getmsg(2), putmsg(2), streamio(7).


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