Eventloop 是什么？是为了解决什么问题而设计的？
1.请问下，Eventloop 是什么？是为了解决什么问题而设计的？
2.下面是Python 版本的Eventloop 实现示例，这里的Eventloop和Javascript中的Eventloop要解决的问题是一样的吗，有什么区别吗？：
class KqueueLoop(object):
MAX_EVENTS = 1024
def __init__(self):
self._kqueue = select.kqueue()
self._fds = {}
def _control(self, fd, mode, flags):
events = []
if mode & POLL_IN:
events.append(select.kevent(fd, select.KQ_FILTER_READ, flags))
if mode & POLL_OUT:
events.append(select.kevent(fd, select.KQ_FILTER_WRITE, flags))
for e in events:
self._kqueue.control([e], 0)
def poll(self, timeout):
if timeout < 0:
timeout = None # kqueue behaviour
events = self._kqueue.control(None, KqueueLoop.MAX_EVENTS, timeout)
results = defaultdict(lambda: POLL_NULL)
for e in events:
fd = e.ident
if e.filter == select.KQ_FILTER_READ:
results[fd] |= POLL_IN
elif e.filter == select.KQ_FILTER_WRITE:
results[fd] |= POLL_OUT
return results.items()
def register(self, fd, mode):
self._fds[fd] = mode
self._control(fd, mode, select.KQ_EV_ADD)
def unregister(self, fd):
self._control(fd, self._fds[fd], select.KQ_EV_DELETE)
del self._fds[fd]
def modify(self, fd, mode):
self.unregister(fd)
self.register(fd, mode)
def close(self):
self.kqueue.close()
class SelectLoop(object):
def __init__(self):
self._r_list = set()
self._w_list = set()
self._x_list = set()
def poll(self, timeout):
r, w, x = select.select(self._r_list, self._w_list, self._x_list,
timeout)
results = defaultdict(lambda: POLL_NULL)
for p in [(r, POLL_IN), (w, POLL_OUT), (x, POLL_ERR)]:
for fd in p[0]:
results[fd] |= p[1]
return results.items()
def register(self, fd, mode):
if mode & POLL_IN:
self._r_list.add(fd)
if mode & POLL_OUT:
self._w_list.add(fd)
if mode & POLL_ERR:
self._x_list.add(fd)
def unregister(self, fd):
if fd in self._r_list:
self._r_list.remove(fd)
if fd in self._w_list:
self._w_list.remove(fd)
if fd in self._x_list:
self._x_list.remove(fd)
def modify(self, fd, mode):
self.unregister(fd)
self.register(fd, mode)
def close(self):
pass
class EventLoop(object):
def __init__(self):
if hasattr(select, 'epoll'):
self._impl = select.epoll()
model = 'epoll'
elif hasattr(select, 'kqueue'):
self._impl = KqueueLoop()
model = 'kqueue'
elif hasattr(select, 'select'):
self._impl = SelectLoop()
model = 'select'
else:
raise Exception('can not find any available functions in select '
'package')
self._fdmap = {} # (f, handler)
self._last_time = time.time()
self._periodic_callbacks = []
self._stopping = False
logging.debug('using event model: %s', model)
def poll(self, timeout=None):
events = self._impl.poll(timeout)
return [(self._fdmap[fd][0], fd, event) for fd, event in events]
def add(self, f, mode, handler):
fd = f.fileno()
self._fdmap[fd] = (f, handler)
self._impl.register(fd, mode)
def remove(self, f):
fd = f.fileno()
del self._fdmap[fd]
self._impl.unregister(fd)
def add_periodic(self, callback):
self._periodic_callbacks.append(callback)
def remove_periodic(self, callback):
self._periodic_callbacks.remove(callback)
def modify(self, f, mode):
fd = f.fileno()
self._impl.modify(fd, mode)
def stop(self):
self._stopping = True
def run(self):
events = []
while not self._stopping:
asap = False
try:
events = self.poll(TIMEOUT_PRECISION)
except (OSError, IOError) as e:
if errno_from_exception(e) in (errno.EPIPE, errno.EINTR):
# EPIPE: Happens when the client closes the connection
# EINTR: Happens when received a signal
# handles them as soon as possible
asap = True
logging.debug('poll:%s', e)
else:
logging.error('poll:%s', e)
import traceback
traceback.print_exc()
continue
for sock, fd, event in events:
handler = self._fdmap.get(fd, None)
if handler is not None:
handler = handler[1]
try:
handler.handle_event(sock, fd, event)
except (OSError, IOError) as e:
shell.print_exception(e)
now = time.time()
if asap or now - self._last_time >= TIMEOUT_PRECISION:
for callback in self._periodic_callbacks:
callback()
self._last_time = now
def __del__(self):
self._impl.close()
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