[gentoo-portage-dev] [PATCH 2/5 v3] Add IndexStreamIterator and MultiIterGroupBy.

[Zac Medico]

This IndexStreamIterator class can be used together with the
pkg_desc_index_line_read function to read an index file incrementally
as a stream.

The MultiIterGroupBy class can be used to iterate over multiple
IndexStreamIterator instances at once, incrementally grouping results
for a particular package from multiple indices, while limiting the
amount of any given index that must be in memory at once.

Both of these classes are used by the  IndexedPortdb class in the next
patch of this series.

X-Gentoo-Bug: 525718
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=525718
---
This updated patch cleans up the logic (possibly fixing bugs), and
optimizes it to avoid over-buffering (memory waste). Also, I added
a TODO note to use a binary search tree to optimize the search
for completed groups.

 pym/portage/cache/index/IndexStreamIterator.py | 27 ++++++++
 pym/portage/util/iterators/MultiIterGroupBy.py | 94 ++++++++++++++++++++++++++
 pym/portage/util/iterators/__init__.py         |  2 +
 3 files changed, 123 insertions(+)
 create mode 100644 pym/portage/cache/index/IndexStreamIterator.py
 create mode 100644 pym/portage/util/iterators/MultiIterGroupBy.py
 create mode 100644 pym/portage/util/iterators/__init__.py

diff --git a/pym/portage/cache/index/IndexStreamIterator.py b/pym/portage/cache/index/IndexStreamIterator.py
new file mode 100644
index 0000000..972aee1
--- /dev/null
+++ b/pym/portage/cache/index/IndexStreamIterator.py
@@ -0,0 +1,27 @@
+# Copyright 2014 Gentoo Foundation
+# Distributed under the terms of the GNU General Public License v2
+
+class IndexStreamIterator(object):
+
+	def __init__(self, f, parser):
+
+		self.parser = parser
+		self._file = f
+
+	def close(self):
+
+		if self._file is not None:
+			self._file.close()
+			self._file = None
+
+	def __iter__(self):
+
+		try:
+
+			for line in self._file:
+				node = self.parser(line)
+				if node is not None:
+					yield node
+
+		finally:
+			self.close()
diff --git a/pym/portage/util/iterators/MultiIterGroupBy.py b/pym/portage/util/iterators/MultiIterGroupBy.py
new file mode 100644
index 0000000..2d8652e
--- /dev/null
+++ b/pym/portage/util/iterators/MultiIterGroupBy.py
@@ -0,0 +1,94 @@
+# Copyright 2014 Gentoo Foundation
+# Distributed under the terms of the GNU General Public License v2
+
+class MultiIterGroupBy(object):
+	"""
+	This class functions similarly to the itertools.groupby function,
+	except that it takes multiple source iterators as input. The source
+	iterators must yield objects in sorted order. A group is yielded as
+	soon as the progress of all iterators reaches a state which
+	guarantees that there can not be any remaining (unseen) elements of
+	the group. This is useful for incremental display of grouped search
+	results.
+	"""
+
+	def __init__(self, iterators, key = None):
+		self._iterators = iterators
+		self._key = key
+
+	def __iter__(self):
+
+		trackers = []
+		for iterator in self._iterators:
+			trackers.append(_IteratorTracker(iterator))
+
+		key_map = {}
+		eof = []
+		key_getter = self._key
+		if key_getter is None:
+			key_getter = lambda x: x
+		min_progress = None
+
+		while trackers:
+
+			for tracker in trackers:
+
+				if tracker.current is not None and \
+					tracker.current != min_progress:
+					# The trackers are sorted by progress, so the
+					# remaining trackers are guaranteed to have
+					# sufficient progress.
+					continue
+
+				# In order to avoid over-buffering (waste of memory),
+				# only grab a single entry.
+				try:
+					entry = next(tracker.iterator)
+				except StopIteration:
+					eof.append(tracker)
+				else:
+					tracker.current = key_getter(entry)
+					key_group = key_map.get(tracker.current)
+					if key_group is None:
+						key_group = []
+						key_map[tracker.current] = key_group
+					key_group.append(entry)
+
+			if eof:
+				for tracker in eof:
+					trackers.remove(tracker)
+				del eof[:]
+
+			if trackers:
+				trackers.sort()
+				min_progress = trackers[0].current
+				yield_these = []
+				# TODO: Use a binary search tree to optimize this loop.
+				for k in key_map:
+					if k <= min_progress:
+						yield_these.append(k)
+			else:
+				yield_these = list(key_map)
+
+			if yield_these:
+				yield_these.sort()
+				for k in yield_these:
+					yield key_map.pop(k)
+
+class _IteratorTracker(object):
+
+	__slots__ = ('current', 'iterator')
+
+	def __init__(self, iterator):
+
+		self.iterator = iterator
+		self.current = None
+
+	def __lt__(self, other):
+		if self.current is None:
+			if other.current is None:
+				return False
+			else:
+				return True
+		return other.current is not None and \
+			self.current < other.current
diff --git a/pym/portage/util/iterators/__init__.py b/pym/portage/util/iterators/__init__.py
new file mode 100644
index 0000000..7cd880e
--- /dev/null
+++ b/pym/portage/util/iterators/__init__.py
@@ -0,0 +1,2 @@
+# Copyright 2014 Gentoo Foundation
+# Distributed under the terms of the GNU General Public License v2
-- 
2.0.4