146 lines
4.2 KiB
Python
146 lines
4.2 KiB
Python
import collections
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from eventlet import api
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from eventlet import queue
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__all__ = ['Pool', 'TokenPool']
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# have to stick this in an exec so it works in 2.4
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try:
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from contextlib import contextmanager
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exec('''
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@contextmanager
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def item_impl(self):
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""" Get an object out of the pool, for use with with statement.
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>>> from eventlet import pools
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>>> pool = pools.TokenPool(max_size=4)
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>>> with pool.item() as obj:
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... print "got token"
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...
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got token
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>>> pool.free()
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4
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"""
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obj = self.get()
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try:
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yield obj
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finally:
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self.put(obj)
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''')
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except ImportError:
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item_impl = None
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class Pool(object):
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"""
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Pool is a base class that is meant to be subclassed. When subclassing,
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define the :meth:`create` method to implement the desired resource.
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When using the pool, if you do a get, you should **always** do a
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:meth:`put`.
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The pattern is::
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thing = self.pool.get()
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try:
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thing.method()
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finally:
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self.pool.put(thing)
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The maximum size of the pool can be modified at runtime via the
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:attr:`max_size` attribute. Adjusting this number does not affect existing
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items checked out of the pool, nor on any waiters who are waiting for an
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item to free up. Some indeterminate number of :meth:`get`/:meth:`put`
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cycles will be necessary before the new maximum size truly matches the
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actual operation of the pool.
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"""
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def __init__(self, min_size=0, max_size=4, order_as_stack=False):
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""" Pre-populates the pool with *min_size* items. Sets a hard limit to
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the size of the pool -- it cannot contain any more items than
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*max_size*, and if there are already *max_size* items 'checked out' of
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the pool, the pool will cause any getter to cooperatively yield until an
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item is put in.
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*order_as_stack* governs the ordering of the items in the free pool.
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If ``False`` (the default), the free items collection (of items that
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were created and were put back in the pool) acts as a round-robin,
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giving each item approximately equal utilization. If ``True``, the
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free pool acts as a FILO stack, which preferentially re-uses items that
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have most recently been used.
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"""
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self.min_size = min_size
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self.max_size = max_size
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self.order_as_stack = order_as_stack
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self.current_size = 0
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self.channel = queue.LightQueue(0)
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self.free_items = collections.deque()
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for x in xrange(min_size):
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self.current_size += 1
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self.free_items.append(self.create())
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def get(self):
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"""Return an item from the pool, when one is available
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"""
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if self.free_items:
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return self.free_items.popleft()
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if self.current_size < self.max_size:
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created = self.create()
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self.current_size += 1
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return created
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return self.channel.get()
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if item_impl is not None:
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item = item_impl
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def put(self, item):
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"""Put an item back into the pool, when done
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"""
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if self.current_size > self.max_size:
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self.current_size -= 1
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return
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if self.waiting():
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self.channel.put(item)
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else:
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if self.order_as_stack:
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self.free_items.appendleft(item)
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else:
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self.free_items.append(item)
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def resize(self, new_size):
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"""Resize the pool
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"""
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self.max_size = new_size
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def free(self):
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"""Return the number of free items in the pool.
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"""
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return len(self.free_items) + self.max_size - self.current_size
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def waiting(self):
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"""Return the number of routines waiting for a pool item.
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"""
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return max(0, self.channel.getting() - self.channel.putting())
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def create(self):
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"""Generate a new pool item
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"""
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raise NotImplementedError("Implement in subclass")
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class Token(object):
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pass
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class TokenPool(Pool):
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"""A pool which gives out tokens (opaque unique objects), which indicate
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that the coroutine which holds the token has a right to consume some
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limited resource.
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"""
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def create(self):
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return Token()
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