How To Use Linux epoll with Python

http://scotdoyle.com/python-epoll-howto.html

Line 1: The select module contains the epoll functionality.
Line 13: Since sockets are blocking by default, this is necessary to use non-blocking (asynchronous) mode.

　　

import socket, select

EOL1 = b'\n\n'
EOL2 = b'\n\r\n'
response  = b'HTTP/1.0 200 OK\r\nDate: Mon, 1 Jan 1996 01:01:01 GMT\r\n'
response += b'Content-Type: text/plain\r\nContent-Length: 13\r\n\r\n'
response += b'Hello, world!'

serversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
serversocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
serversocket.bind(('0.0.0.0', 8080))
serversocket.listen(1)
serversocket.setblocking(0)

epoll = select.epoll()
epoll.register(serversocket.fileno(), select.EPOLLIN)

try:
   connections = {}; requests = {}; responses = {}
   while True:
      events = epoll.poll(1)
      for fileno, event in events:
         if fileno == serversocket.fileno():
            connection, address = serversocket.accept()
            connection.setblocking(0)
            epoll.register(connection.fileno(), select.EPOLLIN)
            connections[connection.fileno()] = connection
            requests[connection.fileno()] = b''
            responses[connection.fileno()] = response
         elif event & select.EPOLLIN:
            requests[fileno] += connections[fileno].recv(1024)
            if EOL1 in requests[fileno] or EOL2 in requests[fileno]:
               epoll.modify(fileno, select.EPOLLOUT)
               print('-'*40 + '\n' + requests[fileno].decode()[:-2])
         elif event & select.EPOLLOUT:
            byteswritten = connections[fileno].send(responses[fileno])
            responses[fileno] = responses[fileno][byteswritten:]
            if len(responses[fileno]) == 0:
               epoll.modify(fileno, 0)
               connections[fileno].shutdown(socket.SHUT_RDWR)
         elif event & select.EPOLLHUP:
            epoll.unregister(fileno)
            connections[fileno].close()
            del connections[fileno]
finally:
   epoll.unregister(serversocket.fileno())
   epoll.close()
   serversocket.close()

　　

epoll的register

 |  register(...)
 |      register(fd[, eventmask]) -> None
 |
 |      Registers a new fd or modifies an already registered fd.
 |      fd is the target file descriptor of the operation.
 |      events is a bit set composed of the various EPOLL constants; the default
 |      is EPOLL_IN | EPOLL_OUT | EPOLL_PRI.
 |
 |      The epoll interface supports all file descriptors that support poll.

　　

Epoll的eventmask

http://man7.org/linux/man-pages/man2/poll.2.html

              POLLIN There is data to read.

              POLLPRI
                     There is urgent data to read (e.g., out-of-band data on
                     TCP socket; pseudoterminal master in packet mode has
                     seen state change in slave).

              POLLOUT
                     Writing is now possible, though a write larger that the
                     available space in a socket or pipe will still block
                     (unless O_NONBLOCK is set).

              POLLRDHUP (since Linux 2.6.17)
                     Stream socket peer closed connection, or shut down
                     writing half of connection.  The _GNU_SOURCE feature
                     test macro must be defined (before including any header
                     files) in order to obtain this definition.

              POLLERR
                     Error condition (output only).

              POLLHUP
                     Hang up (output only).

              POLLNVAL
                     Invalid request: fd not open (output only).

　　

边缘触发(Edge Trigger)和条件触发(Level Trigger)

边缘触发 是指每当状态变化时发生一个io事件；

条件触发 是只要满足条件就发生一个io事件；

http://www.slideshare.net/llj098/epoll-from-the-kernel-side