192 lines
6.3 KiB
Python
192 lines
6.3 KiB
Python
import collections
|
|
|
|
from eventlet import queue
|
|
|
|
__all__ = ['Pool', 'TokenPool']
|
|
|
|
# have to stick this in an exec so it works in 2.4
|
|
try:
|
|
from contextlib import contextmanager
|
|
exec('''
|
|
@contextmanager
|
|
def item_impl(self):
|
|
""" Get an object out of the pool, for use with with statement.
|
|
|
|
>>> from eventlet import pools
|
|
>>> pool = pools.TokenPool(max_size=4)
|
|
>>> with pool.item() as obj:
|
|
... print "got token"
|
|
...
|
|
got token
|
|
>>> pool.free()
|
|
4
|
|
"""
|
|
obj = self.get()
|
|
try:
|
|
yield obj
|
|
finally:
|
|
self.put(obj)
|
|
''')
|
|
except ImportError:
|
|
item_impl = None
|
|
|
|
|
|
|
|
class Pool(object):
|
|
"""
|
|
Pool class implements resource limitation and construction.
|
|
|
|
There are two ways of using Pool: passing a `create` argument or
|
|
subclassing. In either case you must provide a way to create
|
|
the resource.
|
|
|
|
When using `create` argument, pass a function with no arguments::
|
|
|
|
http_pool = pools.Pool(create=httplib2.Http)
|
|
|
|
If you need to pass arguments, build a nullary function with either
|
|
`lambda` expression::
|
|
|
|
http_pool = pools.Pool(create=lambda: httplib2.Http(timeout=90))
|
|
|
|
or :func:`functools.partial`::
|
|
|
|
from functools import partial
|
|
http_pool = pools.Pool(create=partial(httplib2.Http, timeout=90))
|
|
|
|
When subclassing, define only the :meth:`create` method
|
|
to implement the desired resource::
|
|
|
|
class MyPool(pools.Pool):
|
|
def create(self):
|
|
return MyObject()
|
|
|
|
If using 2.5 or greater, the :meth:`item` method acts as a context manager;
|
|
that's the best way to use it::
|
|
|
|
with mypool.item() as thing:
|
|
thing.dostuff()
|
|
|
|
If stuck on 2.4, the :meth:`get` and :meth:`put` methods are the preferred
|
|
nomenclature. Use a ``finally`` to ensure that nothing is leaked::
|
|
|
|
thing = self.pool.get()
|
|
try:
|
|
thing.dostuff()
|
|
finally:
|
|
self.pool.put(thing)
|
|
|
|
The maximum size of the pool can be modified at runtime via
|
|
the :meth:`resize` method.
|
|
|
|
Specifying a non-zero *min-size* argument pre-populates the pool with
|
|
*min_size* items. *max-size* sets a hard limit to the size of the pool --
|
|
it cannot contain any more items than *max_size*, and if there are already
|
|
*max_size* items 'checked out' of the pool, the pool will cause any
|
|
greenthread calling :meth:`get` to cooperatively yield until an item
|
|
is :meth:`put` in.
|
|
"""
|
|
def __init__(self, min_size=0, max_size=4, order_as_stack=False, create=None):
|
|
"""*order_as_stack* governs the ordering of the items in the free pool.
|
|
If ``False`` (the default), the free items collection (of items that
|
|
were created and were put back in the pool) acts as a round-robin,
|
|
giving each item approximately equal utilization. If ``True``, the
|
|
free pool acts as a FILO stack, which preferentially re-uses items that
|
|
have most recently been used.
|
|
"""
|
|
self.min_size = min_size
|
|
self.max_size = max_size
|
|
self.order_as_stack = order_as_stack
|
|
self.current_size = 0
|
|
self.channel = queue.LightQueue(0)
|
|
self.free_items = collections.deque()
|
|
if create is not None:
|
|
self.create = create
|
|
|
|
for x in xrange(min_size):
|
|
self.current_size += 1
|
|
self.free_items.append(self.create())
|
|
|
|
def get(self):
|
|
"""Return an item from the pool, when one is available. This may
|
|
cause the calling greenthread to block.
|
|
"""
|
|
if self.free_items:
|
|
return self.free_items.popleft()
|
|
if self.current_size < self.max_size:
|
|
created = self.create()
|
|
self.current_size += 1
|
|
return created
|
|
return self.channel.get()
|
|
|
|
if item_impl is not None:
|
|
item = item_impl
|
|
|
|
def put(self, item):
|
|
"""Put an item back into the pool, when done. This may
|
|
cause the putting greenthread to block.
|
|
"""
|
|
if self.current_size > self.max_size:
|
|
self.current_size -= 1
|
|
return
|
|
|
|
if self.waiting():
|
|
self.channel.put(item)
|
|
else:
|
|
if self.order_as_stack:
|
|
self.free_items.appendleft(item)
|
|
else:
|
|
self.free_items.append(item)
|
|
|
|
def resize(self, new_size):
|
|
"""Resize the pool to *new_size*.
|
|
|
|
Adjusting this number does not affect existing items checked out of
|
|
the pool, nor on any greenthreads who are waiting for an item to free
|
|
up. Some indeterminate number of :meth:`get`/:meth:`put`
|
|
cycles will be necessary before the new maximum size truly matches
|
|
the actual operation of the pool.
|
|
"""
|
|
self.max_size = new_size
|
|
|
|
def free(self):
|
|
"""Return the number of free items in the pool. This corresponds
|
|
to the number of :meth:`get` calls needed to empty the pool.
|
|
"""
|
|
return len(self.free_items) + self.max_size - self.current_size
|
|
|
|
def waiting(self):
|
|
"""Return the number of routines waiting for a pool item.
|
|
"""
|
|
return max(0, self.channel.getting() - self.channel.putting())
|
|
|
|
def create(self):
|
|
"""Generate a new pool item. In order for the pool to function,
|
|
either this method must be overriden in a subclass or pool must be
|
|
created with `create`=callable argument. It accepts no arguments
|
|
and returns a single instance of whatever thing the pool is supposed
|
|
to contain.
|
|
|
|
In general, :meth:`create` is called whenever the pool exceeds its
|
|
previous high-water mark of concurrently-checked-out-items. In other
|
|
words, in a new pool with *min_size* of 0, the very first call
|
|
to :meth:`get` will result in a call to :meth:`create`. If the first
|
|
caller calls :meth:`put` before some other caller calls :meth:`get`,
|
|
then the first item will be returned, and :meth:`create` will not be
|
|
called a second time.
|
|
"""
|
|
raise NotImplementedError("Implement in subclass")
|
|
|
|
|
|
class Token(object):
|
|
pass
|
|
|
|
|
|
class TokenPool(Pool):
|
|
"""A pool which gives out tokens (opaque unique objects), which indicate
|
|
that the coroutine which holds the token has a right to consume some
|
|
limited resource.
|
|
"""
|
|
def create(self):
|
|
return Token()
|