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Resources which can safely be used by concurrent threads

Project description

A shared resource is some resource identified by an id and used concurrently by several threads. To make the concurrent use safe, calls to resource methods are synchronized.

A resource is obtained by a call to get_resource. The required resource is identified by an id (an arbitrary object adequate as a dictionary key). If a resouce of this id already exists, it is returned. Otherwise, one is created calling the creator and the creator parameters provided to get_resource. The returned value is a wrapper around the resource. The wrapping ensures that calls to the resource’s methods are synchronized.

>>> from dm.sharedresource import get_resource
>>> r = get_resource(1, dict) # a new resource is created with the `dict` creator
>>> r is get_resource(1, dict)
True

The resource behaves quite like the created object. However, calls to its methods are synchronized (i.e. thread safe). However, special methods (those the names of which start and and in __) may not be found (Python 2.4 introduced that some methods must be defined at class creation time and are not longer looked up in the instance). As a special case, __getitem__, __setitem__, __delitem__, __len__, __nonzero__ are explicitely delegated.

>>> r[1] = 1
>>> r[1]
1

Parameters and keyword parameters for the creator can be provided as arguments to get_resource.

>>> r = get_resource('with args', dict, {1:1}, a='a', b='b')
>>> sorted(r.items())
[(1, 1), ('a', 'a'), ('b', 'b')]

Now look that normal classes work as creators, too.

>>> class Resource:
...   def __init__(self, v): self.v = v
...   def f(self): return self.v
...
>>> r = get_resource('class', Resource, 1)
>>> r.f()
1

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1.0

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