如何在 WSGI 处理程序中捕获“[Errno 32] 管道损坏”

WSGI 对于构建高度并发的 HTTP 服务器以支持例如然而，长轮询通常会在某个时刻被客户端结束长时间运行的 HTTP 请求；要清理任何资源并打开句柄，应该向 WSGI 服务器后端通知任何此类事件，但是，目前似乎无法在 WSGI 处理程序中捕获这些事件：

# pseudocode example

def application(env, start_response):
    start_response(...)

    q = Queue()
    ev_handle = register_event_handler(lambda event, arg: q.put((event, arg)))

    # ??? need to call e.g. ev_handle.unregister() when the HTTP request is terminated

    return iter(lambda: render(q.get()), None)

例如，当使用gevent.pywsgi，相应的异常（error: [Errno 32] Broken pipe) 被抛出到 gevent 内部的某个地方，并且似乎从未出现在处理程序可能看到它的任何地方：

Traceback (most recent call last):
  File "/Users/erik.allik/.virtualenvs/myproj/lib/python2.7/site-packages/gevent/pywsgi.py", line 508, in handle_one_response
    self.run_application()
  File "/Users/erik.allik/.virtualenvs/myproj/lib/python2.7/site-packages/gevent/pywsgi.py", line 495, in run_application
    self.process_result()
  File "/Users/erik.allik/.virtualenvs/myproj/lib/python2.7/site-packages/gevent/pywsgi.py", line 486, in process_result
    self.write(data)
  File "/Users/erik.allik/.virtualenvs/myproj/lib/python2.7/site-packages/gevent/pywsgi.py", line 376, in write
    self._write(data)
  File "/Users/erik.allik/.virtualenvs/myproj/lib/python2.7/site-packages/gevent/pywsgi.py", line 369, in _write
    self._sendall(data)
  File "/Users/erik.allik/.virtualenvs/myproj/lib/python2.7/site-packages/gevent/pywsgi.py", line 355, in _sendall
    self.socket.sendall(data)
  File "/Users/erik.allik/.virtualenvs/myproj/lib/python2.7/site-packages/gevent/socket.py", line 458, in sendall
    data_sent += self.send(_get_memory(data, data_sent), flags)
  File "/Users/erik.allik/.virtualenvs/myproj/lib/python2.7/site-packages/gevent/socket.py", line 435, in send
    return sock.send(data, flags)

看起来当请求终止时会发生什么，除了（看似无法捕获的）异常回溯之外，从 WSGI 处理程序返回的迭代器是.close()-d。因此可以确定何时应关闭与响应关联的任何工作人员/资源/句柄。基本上就是这样werkzeug.wsgi.ClosingIterator https://github.com/mitsuhiko/werkzeug/blob/master/werkzeug/wsgi.py#L643 does:

class ClosingIterator(object):
    def __init__(self, iterable, on_close):
        iterator = iter(iterable)
        self.close = on_close
    def __iter__(self):
        return self
    def __next__(self):
        return self._next()

def application(env, start_response):
    start_response(...)

    q = Queue()
    ev_handle = register_event_handler(lambda event, arg: q.put((event, arg)))

    return ClosingIterator(
        iter(lambda: render(q.get()), None),
        on_close=ev_handle.unregister
    )

然而，这并没有消除错误消息/回溯，但这似乎是可以容忍的，除非有人能想出一个可以解决这个问题的解决方案。