event_loop.py

# python3

import collections
import errno
import heapq
import json
import random
import selectors
import socket as _socket
import sys
import time


class EventLoop:
    def __init__(self):
        self._queue = Queue()
        self._time = None

    def run(self, entry_point, *args):
        self._execute(entry_point, *args)

        while not self._queue.is_empty():
            fn, mask = self._queue.pop(self._time)
            self._execute(fn, mask)

        self._queue.close()

    def register_fileobj(self, fileobj, callback):
        self._queue.register_fileobj(fileobj, callback)

    def unregister_fileobj(self, fileobj):
        self._queue.unregister_fileobj(fileobj)

    def set_timer(self, duration, callback):
        self._time = hrtime()
        self._queue.register_timer(self._time + duration,
                                   lambda _: callback())

    def _execute(self, callback, *args):
        self._time = hrtime()
        try:
            callback(*args)  # new callstack starts
        except Exception as err:
            print('Uncaught exception:', err)
        self._time = hrtime()


class Queue:
    def __init__(self):
        self._selector = selectors.DefaultSelector()
        self._timers = []
        self._timer_no = 0
        self._ready = collections.deque()

    def register_timer(self, tick, callback):
        timer = (tick, self._timer_no, callback)
        heapq.heappush(self._timers, timer)
        self._timer_no += 1

    def register_fileobj(self, fileobj, callback):
        self._selector.register(fileobj,
                selectors.EVENT_READ | selectors.EVENT_WRITE,
                callback)

    def unregister_fileobj(self, fileobj):
        self._selector.unregister(fileobj)

    def pop(self, tick):
        if self._ready:
            return self._ready.popleft()

        timeout = None
        if self._timers:
            timeout = (self._timers[0][0] - tick) / 10e6

        events = self._selector.select(timeout)
        for key, mask in events:
            callback = key.data
            self._ready.append((callback, mask))

        if not self._ready and self._timers:
            idle = (self._timers[0][0] - tick)
            if idle > 0:
                time.sleep(idle / 10e6)
                return self.pop(tick + idle)

        while self._timers and self._timers[0][0] <= tick:
            _, _, callback = heapq.heappop(self._timers)
            self._ready.append((callback, None))

        return self._ready.popleft()

    def is_empty(self):
        return not (self._ready or self._timers or self._selector.get_map())

    def close(self):
        self._selector.close()


class Context:
    _event_loop = None

    @classmethod
    def set_event_loop(cls, event_loop):
        cls._event_loop = event_loop

    @property
    def evloop(self):
        return self._event_loop


class IOError(Exception):
    def __init__(self, message, errorno, errorcode):
        super().__init__(message)
        self.errorno = errorno
        self.errorcode = errorcode

    def __str__(self):
        return super().__str__() + f' (error {self.errorno} {self.errorcode})'


def hrtime():
    """ returns time in microseconds """
    return int(time.time() * 10e6)


class set_timer(Context):
    def __init__(self, duration, callback):
        """ duration is in microseconds """
        self.evloop.set_timer(duration, callback)


class socket(Context):
    def __init__(self, *args):
        self._sock = _socket.socket(*args)
        self._sock.setblocking(False)
        self.evloop.register_fileobj(self._sock, self._on_event)
        # 0 - initial
        # 1 - connecting
        # 2 - connected
        # 3 - closed
        self._state = 0
        self._callbacks = {}

    def connect(self, addr, callback):
        assert self._state == 0
        self._state = 1
        self._callbacks['conn'] = callback
        err = self._sock.connect_ex(addr)
        assert errno.errorcode[err] == 'EINPROGRESS'

    def recv(self, n, callback):
        assert self._state == 2
        assert 'recv' not in self._callbacks

        def _on_read_ready(err):
            if err:
                return callback(err)
            data = self._sock.recv(n)
            callback(None, data)

        self._callbacks['recv'] = _on_read_ready

    def sendall(self, data, callback):
        assert self._state == 2
        assert 'sent' not in self._callbacks

        def _on_write_ready(err):
            nonlocal data
            if err:
                return callback(err)

            n = self._sock.send(data)
            if n < len(data):
                data = data[n:]
                self._callbacks['sent'] = _on_write_ready
            else:
                callback(None)

        self._callbacks['sent'] = _on_write_ready

    def close(self):
        self.evloop.unregister_fileobj(self._sock)
        self._callbacks.clear()
        self._state = 3
        self._sock.close()

    def _on_event(self, mask):
        if self._state == 1:
            assert mask == selectors.EVENT_WRITE
            cb = self._callbacks.pop('conn')
            err = self._get_sock_error()
            if err:
                self.close()
            else:
                self._state = 2
            cb(err)

        if mask & selectors.EVENT_READ:
            cb = self._callbacks.get('recv')
            if cb:
                del self._callbacks['recv']
                err = self._get_sock_error()
                cb(err)

        if mask & selectors.EVENT_WRITE:
            cb = self._callbacks.get('sent')
            if cb:
                del self._callbacks['sent']
                err = self._get_sock_error()
                cb(err)

    def _get_sock_error(self):
        err = self._sock.getsockopt(_socket.SOL_SOCKET,
                                    _socket.SO_ERROR)
        if not err:
            return None
        return IOError('connection failed',
                       err, errno.errorcode[err])

###############################################################################

class Client:
    def __init__(self, addr):
        self.addr = addr

    def get_user(self, user_id, callback):
        self._get(f'GET user {user_id}\n', callback)

    def get_balance(self, account_id, callback):
        self._get(f'GET account {account_id}\n', callback)

    def _get(self, req, callback):
        sock = socket(_socket.AF_INET, _socket.SOCK_STREAM)

        def _on_conn(err):
            if err:
                return callback(err)

            def _on_sent(err):
                if err:
                    sock.close()
                    return callback(err)

                def _on_resp(err, resp=None):
                    sock.close()
                    if err:
                        return callback(err)
                    callback(None, json.loads(resp))

                sock.recv(1024, _on_resp)

            sock.sendall(req.encode('utf8'), _on_sent)

        sock.connect(self.addr, _on_conn)


def get_user_balance(serv_addr, user_id, done):
    client = Client(serv_addr)

    def on_timer():

        def on_user(err, user=None):
            if err:
                return done(err)

            def on_account(err, acc=None):
                if err:
                    return done(err)
                done(None, f'User {user["name"]} has {acc["balance"]} USD')

            if user_id % 5 == 0:
                raise Exception('Do not throw from callbacks')
            client.get_balance(user['account_id'], on_account)

        client.get_user(user_id, on_user)

    set_timer(random.randint(0, int(10e6)), on_timer)


def main1(serv_addr):
    def on_balance(err, balance=None):
        if err:
            print('ERROR', err)
        else:
            print(balance)

    for i in range(10):
        get_user_balance(serv_addr, i, on_balance)


def main2(*args):
  sock = socket(_socket.AF_INET, _socket.SOCK_STREAM)

  def on_conn(err):
    if err:
      return print(err)

    def on_sent(err):
      if err:
        sock.close()
        return print(err)

      def on_resp(err, resp=None):
        sock.close()
        if err:
          return print(err)
        print(resp)

      sock.recv(1024, on_resp)

    sock.sendall(b'GET / HTTP/1.1\r\nHost: t.co\r\n\r\n', on_sent)

  sock.connect(('t.co', 80), on_conn)


if __name__ == '__main__':
    print('Run main1()')
    event_loop = EventLoop()
    Context.set_event_loop(event_loop)

    serv_addr = ('127.0.0.1', int(sys.argv[1]))
    event_loop.run(main1, serv_addr)

    print('\nRun main2()')
    event_loop = EventLoop()
    Context.set_event_loop(event_loop)
    event_loop.run(main2)