Dispatcher - wait on multiple file descriptors until a condition occurs

       Conceptually,  the dispatcher plays the role of detecting new data on multiple input file descriptors and
       dispatching the data to the appropriate iohandlers.  The dispatcher also notifies iohandlers  of  expired
       timers.   Notification  of  either  an  I/O  condition  or  an expired timer occurs by calling one of the
       iohandler's virtual  functions  (see  IOHandler(3I)).   Since  a  program  needs  only  one  instance  of
       Dispatcher, a static member function is provided to create that instance if necessary and return it.

       Dispatcher - wait on multiple file descriptors until a condition occurs

enumDispatcherMask{ReadMask,WriteMask,ExceptMask}virtualIOHandler*handler(intfd,DispatcherMask)virtualvoidlink(intfd,DispatcherMask,IOHandler*)virtualvoidunlink(intfd)
              Return  a  file  descriptor's  iohandler, link a file descriptor to an iohandler, or unlink a file
              descriptor from its iohandlers.  The DispatcherMask describes the I/O condition that the iohandler
              is interested in, such as whether the file descriptor has new data available for reading.  If  the
              I/O  condition occurs, the iohandler will be expected to read data from the file descriptor, write
              data to the file descriptor, or handle the exception depending on the I/O condition.

       virtualvoidstartTimer(longsec,longusec,IOHandler*)virtualvoidstopTimer(IOHandler*)
              Attach an iohandler to a timer or remove a timer before it expires.  A  timer  expires  after  the
              given  number  of  seconds and microseconds have elapsed.  If a timer expires, the dispatcher will
              notify the attached iohandler.  Timers will not expire until the program calls either  variant  of
              Dispatcher::dispatch.

       virtualvoiddispatch()virtualbooleandispatch(long&sec,long&usec)
              With  no  arguments,  block indefinitely until an I/O condition occurs or a timer expires and then
              notify the attached iohandler.  With two arguments, block no  longer  than  the  given  number  of
              seconds  and  microseconds.   If both numbers are zero, the function will return immediately after
              checking all file descriptors and timers.  The return value will  be  true  if  an  I/O  condition
              caused  the  function  to  return and false if the function returned because a timer expired or it
              exceeded the given poll time.  The function will decrease the given poll time  by  the  amount  of
              time it spent blocking.

       staticDispatcher&instance()staticvoidinstance(Dispatcher*)
              With  no  arguments,  create  an instance of Dispatcher if it doesn't already exist and return it.
              With an argument, set the instance of Dispatcher that will be used throughout the program.

select(2), IOHandler(3I)

InterViews                                      21 December 1990                                  Dispatcher(3I)

#include<Dispatch/dispatcher.h>