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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def flush(self):
 """Synchronously wait until this work item is processed. This has the effect of waiting until all work items queued before this method has been called have finished. """


        done = threading.Event()

        def _callback():
            done.set()

        self.defer(_callback)
        done.wait()