how gevent works?

gevent_demo.py

# gevent from the ground up - demo 1

import selectors
import socket
import time
from urllib.parse import urlparse


sel = selectors.DefaultSelector()


class Task(object):
    def __init__(self):
        self._state = 'STARTED'
        self.result = None

    def set_result(self, result):
        self.result = result
        self._state = 'FINISHED'

    @property
    def done(self):
        return self._state == 'FINISHED'


class HttpRequest(object):
    def __init__(self, method, url):
        self._method = method
        self._url = url
        self._buf = bytearray()
        self._task = Task()

    def start(self):
        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        parse_result = urlparse(self._url)
        sock.connect((parse_result.hostname, parse_result.port or 80))
        sock.send(b'%b / HTTP/1.1\r\n\r\n' % bytes(self._method, 'ascii'))
        sock.setblocking(False)
        sel.register(sock, selectors.EVENT_READ, self._read_cb)
        yield self._task

    def _read_cb(self, conn, mask):
        data = conn.recv(16)
        if data == b'':
            self._task.set_result(self._buf[:])
            sel.unregister(conn)
            conn.close()
            return True
        self._buf.extend(data)



class Hub(object):
    def __init__(self):
        self.to_finish = {}

    def run(self):
        # event loop
        while 1:
            if not self.to_finish:
                yield self

            events = sel.select()
            for key, mask in events:
                callback = key.data
                callback(key.fileobj, mask)

                if all([task.done for task in self.to_finish.values()]):
                    self.to_finish = {}


hub = Hub()
hub_coro = hub.run()


def spawn(coro):
    task = next(coro)
    return task


def joinall(tasks):
    for task in tasks:
        hub.to_finish[id(task)] = task
    try:
        next(hub_coro)
    except StopIteration:
        pass


tasks = [spawn(HttpRequest('GET', 'http://www.douban.com').start()),
         spawn(HttpRequest('GET', 'http://www.example.org').start())]

start = time.time()
joinall(tasks)
print('async', time.time() - start)

• 一个生成器相当与一个 greenlet
• Hub 和 gevent 中的 Hub 有点相似

通过这个例子，可以了解

• gevent 的大致工作原理
• greenlet 调度机制？

据说 greenlet 的调度原理也很值得研究，但目前还不太懂。