James Y Knight ha scritto:
On May 11, 2008, at 6:15 PM, Christopher Stawarz wrote:
Abstract
--------
This specification defines a set of extensions that allow WSGI
applications to run effectively on asynchronous (aka event driven)
servers.
Rationale
---------
The architecture of an asynchronous server requires all I/O
operations, including both interprocess and network communication, to
be non-blocking. For a WSGI-compliant server, this requirement
extends to all applications run on the server. However, the WSGI
specification does not provide sufficient facilities for an
application to ensure that its I/O is non-blocking. Specifically,
there are two issues:
* The methods provided by the input stream (``environ['wsgi.input']``)
follow the semantics of the corresponding methods of the ``file``
class.
* WSGI does not provide the application with a mechanism to test
arbitrary file descriptors (such as those belonging to sockets or
pipes opened by the application) for I/O readiness.
There are other issues. How do you do a DNS lookup? How do you get
process completion notification? Heck, how do you run a process? Once
you have I/O readiness information, what do you do with that? I guess
you'd need to write a whole new asynchronous server framework on top of
AWSGI? I can't see being able to use it "raw" for any real applications.
This is not a problem with AWSGI.
As an example there are libraries like PostgreSQL and curl that can be
used with an external event loop.
In the WSGI implementation for Nginx I can provide an interface for
using the builtin supporto for asynchronous DNS client.
The first argument, ``fd``, is either an integer representing a file
descriptor or an object with a ``fileno`` method that returns such an
integer. (In addition, ``fd`` may be ``x-wsgiorg.async.input``, even
if it lacks a ``fileno`` method.) The second, optional argument,
``timeout``, is either ``None`` or a floating-point value in seconds.
If omitted, it defaults to ``None``.
What if the event-loop of the server doesn't use integer fds, but
windows file handles or a java channel object? Where are you allowed to
get these integers from? Is it always a socket from
socket.socket().fileno()? Or can it be a file from open().fileno() or
os.open()? A pipe from os.pipe()? Note that these distinctions are
important everywhere but UNIX.
This has the same problems that we have with wsgi.file_wrapper.
This is the reason, among other things, why the API in my implementation
uses ngx.connection_wrapper and ngx.poll_register
> [...]
Manlio Perillo
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