Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/1977#discussion_r28027864
--- Diff: python/pyspark/shuffle.py ---
@@ -529,6 +522,322 @@ def sorted(self, iterator, key=None, reverse=False):
return heapq.merge(chunks, key=key, reverse=reverse)
+class ExternalList(object):
+ """
+ ExternalList can have many items which cannot be hold in memory in
+ the same time.
+
+ >>> l = ExternalList(range(100))
+ >>> len(l)
+ 100
+ >>> l.append(10)
+ >>> len(l)
+ 101
+ >>> for i in range(10240):
+ ... l.append(i)
+ >>> len(l)
+ 10341
+ >>> import pickle
+ >>> l2 = pickle.loads(pickle.dumps(l))
+ >>> len(l2)
+ 10341
+ >>> list(l2)[100]
+ 10
+ """
+ LIMIT = 10240
+
+ def __init__(self, values):
+ self.values = values
+ self.count = len(values)
+ self._file = None
+ self._ser = None
+
+ def __getstate__(self):
+ if self._file is not None:
+ self._file.flush()
+ f = os.fdopen(os.dup(self._file.fileno()))
+ f.seek(0)
+ serialized = f.read()
+ else:
+ serialized = ''
+ return self.values, self.count, serialized
+
+ def __setstate__(self, item):
+ self.values, self.count, serialized = item
+ if serialized:
+ self._open_file()
+ self._file.write(serialized)
+ else:
+ self._file = None
+ self._ser = None
+
+ def __iter__(self):
+ if self._file is not None:
+ self._file.flush()
+ # read all items from disks first
+ with os.fdopen(os.dup(self._file.fileno()), 'r') as f:
+ f.seek(0)
+ for values in self._ser.load_stream(f):
+ for v in values:
--- End diff --
I understand now that this is just unwrapping the list that we wrapped
around `self.values` in the `_spill` call down on line 615, but this was a bit
confusing to me. If we need to keep this and the wrapping, could you add
comments to explain it?
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