select.txt
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select - manage several sockets (or files) at once - in a single thread

  like socket, select API is from Unix + C ca 1980
   now similar in most OS and languages

  Socket accept, send, recv are blocking operations
   program stops and waits for awaited event to occur
   other events are ignored while program is waiting
  How can we handle several sockets?
   would like to recv from whichever socket as data
  select can wait for several sockets (and/or files) at once
   recall the keyboard is also a "file" - sys.stdin







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select - how it works

  server = socket. ...
  ...
  input = [server,sys.stdin] # list of sockets and file-like objects
  ... 
  while running:
     inputready,outputready,exceptready = select.select(input,[],[],timeout)

  Args are lists of sockets (files) where we are waiting for input,
    output, and exception
  Waits for *all* at once.  Returns when awaited input (etc) appears on *any*
  Returns lists of sockets (etc.) where input (etc) actually is ready
  Optional timeout arg, returns when timer expires - periodic heartbeat
   (see echo_server_select.py)






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Select - limitations

 Doesn't scale to thousands of connections - "c10k"
 Alternatives: epoll, kqueue, asyncore, gevent, twisted, greenlets, ...