[Twisted-Python] feedback requested -- flow.py goes beta

Clark C. Evans cce at clarkevans.com
Sat Apr 19 15:55:54 EDT 2003

When to use flow?

  For simple processes which can be broken down into
  a small set of chunks, then Deferred is the best way
  to go.  To make it worth while to use flow, you need
  one of the following:

    a) incremental results: for example, a big or slow
       executing database query that needs to process
       results as they become available.
    b) merging or splitting: for example, having two
       database queries running in parallel, the
       results being merged together

    c) complicated chunking: if your deferred chunks
       start to get numerous or have non-trivial logic
       in them, then flow would be useful.

    d) intensive computations: if your process has
       computations that need to be broken into
       chunks, then flow may be better than deferreds.

Recent changes:

   I renamed flow.ThreadedIterator to flow.Threaded,
   as it is now a wrapper (you don't inherit).


On Thu, Apr 17, 2003 at 04:09:57PM +0000, Clark C. Evans wrote:
| Abstract: >
|    The flow module implements cooperative multi-tasking using
|    iterators (easily created with generators) and Twisted's 
|    event reactor.   The flow module also includes support for
|    incrementally returning query results from Twisted's 
|    database connection pool.  While this module does _not_ 
|    require generators (a python v2.2 feature), applications 
|    of the module are best demonstrated with generators.
| Status: >
|    The flow module (flow.py) is currently checked into CVS in
|    the sandbox directory.  It is unlikely that any large 
|    changes to the module will happen.   The documentation 
|    is partial, but currently in development.
|    General feedback from the Twisted Community is requested.
| Deployment: >
|    If flow was accepted into twisted, I was thinking 
|    of spreading its functionality over several files.
|    1.  Adding a base implementation module, twisted.python.flow,
|        which only depends upon other items in twisted.python
|    2.  Adding a (fairly small) Flow class to 
|        twisted.internet.defer which takes the base
|        implementation and uses the reactor and inherits
|        from Deferrred.
|    3.  Adding a ThreadedIterator class to twisted.internet.threads
|        which depends upon twisted.internet.reactor and 
|        twisted.python.*
|    4.  Adding a (fairly small) QueryIterator class to 
|        twisted.enterprise.adbapi which depends primarly 
|        on ThreadedIterator, but provides for query 
|        functionality from a ConnectionPool
| Best,
| Clark
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