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|
import errno
import select
from redis.exceptions import RedisError
_DEFAULT_SELECTOR = None
class BaseSelector(object):
"""
Base class for all Selectors
"""
def __init__(self, sock):
self.sock = sock
def can_read(self, timeout=0):
"""
Return True if data is ready to be read from the socket,
otherwise False.
This doesn't guarentee that the socket is still connected, just that
there is data to read.
Automatically retries EINTR errors based on PEP 475.
"""
while True:
try:
return self.check_can_read(timeout)
except (select.error, IOError) as ex:
if self.errno_from_exception(ex) == errno.EINTR:
continue
return False
def is_ready_for_command(self, timeout=0):
"""
Return True if the socket is ready to send a command,
otherwise False.
Automatically retries EINTR errors based on PEP 475.
"""
while True:
try:
return self.check_is_ready_for_command(timeout)
except (select.error, IOError) as ex:
if self.errno_from_exception(ex) == errno.EINTR:
continue
return False
def check_can_read(self, timeout):
"""
Perform the can_read check. Subclasses should implement this.
"""
raise NotImplementedError
def check_is_ready_for_command(self, timeout):
"""
Perform the is_ready_for_command check. Subclasses should
implement this.
"""
raise NotImplementedError
def close(self):
"""
Close the selector.
"""
self.sock = None
def errno_from_exception(self, ex):
"""
Get the error number from an exception
"""
if hasattr(ex, 'errno'):
return ex.errno
elif ex.args:
return ex.args[0]
else:
return None
if hasattr(select, 'select'):
class SelectSelector(BaseSelector):
"""
A select-based selector that should work on most platforms.
This is the worst poll strategy and should only be used if no other
option is available.
"""
def check_can_read(self, timeout):
"""
Return True if data is ready to be read from the socket,
otherwise False.
This doesn't guarentee that the socket is still connected, just
that there is data to read.
"""
return bool(select.select([self.sock], [], [], timeout)[0])
def check_is_ready_for_command(self, timeout):
"""
Return True if the socket is ready to send a command,
otherwise False.
"""
r, w, e = select.select([self.sock], [self.sock], [self.sock],
timeout)
return bool(w and not r and not e)
if hasattr(select, 'poll'):
class PollSelector(BaseSelector):
"""
A poll-based selector that should work on (almost?) all versions
of Unix
"""
_EVENT_MASK = (select.POLLIN | select.POLLPRI | select.POLLOUT |
select.POLLERR | select.POLLHUP)
_READ_MASK = select.POLLIN | select.POLLPRI
_WRITE_MASK = select.POLLOUT
def __init__(self, sock):
super(PollSelector, self).__init__(sock)
self.poller = select.poll()
self.poller.register(sock, self._EVENT_MASK)
def close(self):
"""
Close the selector.
"""
try:
self.poller.unregister(self.sock)
except (KeyError, ValueError):
# KeyError is raised if somehow the socket was not registered
# ValueError is raised if the socket's file descriptor is
# negative.
# In either case, we can't do anything better than to remove
# the reference to the poller.
pass
self.poller = None
self.sock = None
def check_can_read(self, timeout=0):
"""
Return True if data is ready to be read from the socket,
otherwise False.
This doesn't guarentee that the socket is still connected, just
that there is data to read.
"""
events = self.poller.poll(0)
return bool(events and events[0][1] & self._READ_MASK)
def check_is_ready_for_command(self, timeout=0):
"""
Return True if the socket is ready to send a command,
otherwise False
"""
events = self.poller.poll(0)
return bool(events and events[0][1] == self._WRITE_MASK)
def has_selector(selector):
"Determine if the current platform has the selector available"
try:
if selector == 'poll':
# the select module offers the poll selector even if the platform
# doesn't support it. Attempt to poll for nothing to make sure
# poll is available
p = select.poll()
p.poll(0)
else:
# the other selectors will fail when instantiated
getattr(select, selector)().close()
return True
except (OSError, AttributeError):
return False
def DefaultSelector(sock):
"Return the best selector for the platform"
global _DEFAULT_SELECTOR
if _DEFAULT_SELECTOR is None:
if has_selector('poll'):
_DEFAULT_SELECTOR = PollSelector
elif hasattr(select, 'select'):
_DEFAULT_SELECTOR = SelectSelector
else:
raise RedisError('Platform does not support any selectors')
return _DEFAULT_SELECTOR(sock)
|
