model.py 文件源码

def global_cache(srctype, ffi, funcname, *args, **kwds):
    key = kwds.pop('key', (funcname, args))
    assert not kwds
    try:
        return ffi._backend.__typecache[key]
    except KeyError:
        pass
    except AttributeError:
        # initialize the __typecache attribute, either at the module level
        # if ffi._backend is a module, or at the class level if ffi._backend
        # is some instance.
        if isinstance(ffi._backend, types.ModuleType):
            ffi._backend.__typecache = weakref.WeakValueDictionary()
        else:
            type(ffi._backend).__typecache = weakref.WeakValueDictionary()
    try:
        res = getattr(ffi._backend, funcname)(*args)
    except NotImplementedError as e:
        raise NotImplementedError("%s: %r: %s" % (funcname, srctype, e))
    # note that setdefault() on WeakValueDictionary is not atomic
    # and contains a rare bug (http://bugs.python.org/issue19542);
    # we have to use a lock and do it ourselves
    cache = ffi._backend.__typecache
    with global_lock:
        res1 = cache.get(key)
        if res1 is None:
            cache[key] = res
            return res
        else:
            return res1