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(python2.1-lib.info)Polling Objects

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Polling Objects
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The `poll()' system call, supported on most Unix systems, provides
better scalability for network servers that service many, many clients
at the same time.  `poll()' scales better because the system call only
requires listing the file descriptors of interest, while `select()'
builds a bitmap, turns on bits for the fds of interest, and then
afterward the whole bitmap has to be linearly scanned again.
`select()' is O(highest file descriptor), while `poll()' is O(number of
file descriptors).

`register(fd[, eventmask])'
     Register a file descriptor with the polling object.  Future calls
     to the `poll()' method will then check whether the file descriptor
     has any pending I/O events.  FD can be either an integer, or an
     object with a `fileno()' method that returns an integer.  File
     objects implement `fileno()', so they can also be used as the
     argument.

     EVENTMASK is an optional bitmask describing the type of events you
     want to check for, and can be a combination of the constants
     `POLLIN', `POLLPRI', and `POLLOUT', described in the table below.
     If not specified, the default value used will check for all 3
     types of events.

     Constant                           Meaning
     ------                             -----
     POLLIN                             There is data to read
     POLLPRI                            There is urgent data to read
     POLLOUT                            Ready for output: writing will
                                        not block
     POLLERR                            Error condition of some sort
     POLLHUP                            Hung up
     POLLNVAL                           Invalid request: descriptor not
                                        open

     Registering a file descriptor that's already registered is not an
     error, and has the same effect as registering the descriptor
     exactly once.

`unregister(fd)'
     Remove a file descriptor being tracked by a polling object.  Just
     like the `register()' method, FD can be an integer or an object
     with a `fileno()' method that returns an integer.

     Attempting to remove a file descriptor that was never registered
     causes a `KeyError' exception to be raised.

`poll([timeout])'
     Polls the set of registered file descriptors, and returns a
     possibly-empty list containing `(FD, EVENT)' 2-tuples for the
     descriptors that have events or errors to report.  FD is the file
     descriptor, and EVENT is a bitmask with bits set for the reported
     events for that descriptor -- `POLLIN' for waiting input,
     `POLLOUT' to indicate that the descriptor can be written to, and
     so forth.  An empty list indicates that the call timed out and no
     file descriptors had any events to report.  If TIMEOUT is given,
     it specifies the length of time in milliseconds which the system
     will wait for events before returning.  If TIMEOUT is omitted,
     negative, or `None', the call will block until there is an event
     for this poll object.