
select(+StreamList, +Timeout, ?ReadyStreams)

   Returns streams from StreamList which are ready for I/O, blocking at most
Timeout seconds.



Arguments
   +StreamList         A list of atoms or integers.
   +Timeout            A number or an atom.
   ?ReadyStreams       A term unifyable with a list of integers and atoms.

Type
   Stream I/O

Description
   select/3 is modelled after (and partially implemented using) the
   select() Unix system call.  StreamList is a list of streams where
   input or output is expected to occur.  If I/O is available on some
   streams from the StreamList, ReadyStreams is unified with a list of
   those. The same symbolic stream names are used in both lists.


   If Timeout is a number, it must be non-negative and less than
   100000000 select/3 then waits for at most Timeout seconds for I/O
   on these streams and if none is available, it unifies ReadyStreams
   with nil.  If Timeout is zero, select/3 does not wait but it
   immediately returns the list of streams where I/O is available.  If
   Timeout is the atom block, select/3 waits until I/O is possible on
   one of the streams in StreamList.


   The streams in StreamList can be sockets, queues or string streams. 
   On Unix systems, pipes, files and ttys are also allowed.  Unlike the
   select() system call, select does not test any exceptional pending
   conditions.


Note
   Currently it is not possible to return sockets on which output is
   possible.




Resatisfiable
      No.

Fail Conditions
      Fails if ReadyStreams does not unify with the sublist of StreamList
   containing streams with available I/O.



Exceptions
     4 --- StreamList is not instantiated or it contains uninstantiated    variables.
     4 --- Timeout is not instantiated.
     5 --- StreamList is not a list of integers and atoms.
     5 --- Timeout instantiated, but not to a number or an atom.
     5 --- ReadyStreams is instantiated, but not to a list or nil
     6 --- Timeval is a negative number or an atom different from block.
   141 --- Not implemented for this stream class on this system.
   170 --- The system call was interrupted by a signal.
   192 --- A stream in StreamList is not an input stream or a pipe,    or it is a string stream or null.
   193 --- A stream in StreamList is not open or does not exist.

Examples
   
     [eclipse 1]: socket(internet, datagram, s), bind(s, _/40000),
		  socket(internet, datagram, r), bind(r, _/40001),
		  select([s, r], block, Streams).

     <blocks until data arrives>



     [eclipse 1]: open(queue(""), update, q).
     yes.
     [eclipse 2]: select([q],0,L).
     L = []
     yes.
     [eclipse 3]: write(q,hello).
     yes.
     [eclipse 4]: select([q],0,L).
     L = [q]
     yes.






See Also
   open / 3, open / 4, pipe / 2, socket / 3, get_stream_info / 3
