[Twisted-Python] flow module release canidate and future schedule

[Clark C. Evans]

Hello.  Over this last week, quite alot of work has been put into
the flow module.   As of today, I have other responsibilities which
I must attend... but flow is being used in one of my internal
projects at Axista, Inc. and is quite stable.

I encourage people to try it out.. it's quite nice if
I don't say so myself.

What is flow?

  Flow is a module which leverages generators to provide for
  incremental result multi-stage operations (like http requests) 
  which can cooperate with other operations without blocking.
  See sandbox/flow.html for more information

Current Status:

  0. The documentation (flow.html) is now much more clear
     and "up-to-date" with respect to newer changes.  Please
     take it for a spin.  All of the examples are full-fledged
     programs and should run.

  1. Flow is quite faster now, about 2-3x from the previous
     versions.  This is due to some significant profiling and
     an enhancement proposed by exarkun; in particular, each 
     yield can support returning a row set rather than a 
     single row.  This is a boon for database applications.

  2. Flow supports protocols with one callback, which should
     handle most protocol requirements.   An echo 'client' and
     echo 'server' are included in sandbox/cce/echo.py

  3. Several 'helpers' such as Merge, Zip, are now available
     and well tested (Merge isn't perfect yet though).

  4. Flow supports not only deferreds, but also callbacks;
     this is flow.Callback, which is used, not suprizingly,
     by flow.Protocol 

  5. The "Instruction" mechanism has been revamped to support
     'CallLater' instructions.  This is an internal refactor
     which cleaned up alot of code.

  6. The test suite has been greatly expanded to test these
     items.

Future Directions:

  1. As I start playing with more protocols, I'll probably add
     a few 'filters' which would take a raw flow.Protocol and
     return items by line or by a specified chunk size.

  2. The 'Merge' code needs some reviewing as it isn't perfect
     and doesn't behave quite right yet.   I don't have any
     serious use case for this right now, so it may not get
     fixed for another month or so.

  3. Eventually (probably late this year) I'll consider writing
     flow as a "C" module for speed.  This should be about 2-3x
     faster in most cases.   So, if you are not using flow beacuse
     of speed concerns, keep this in mind and let me know.

Best,

Clark