Memory usage reducer, based on a post to the mailing-list by Christian Nilsendahl

waflib/extras/mem_reducer.py

@@ -0,0 +1,66 @@
+#! /usr/bin/env python
+# encoding: UTF-8
+
+"""
+This tool can help to reduce the memory usage in very large builds featuring many tasks with after/before attributes.
+
+Usage:
+def options(opt):
+	opt.load('mem_reducer')
+"""
+
+import itertools
+from waflib import Utils, Task
+
+class SetOfTasks(object):
+	"""Wraps a set and a task which has a list of other sets.
+	The interface is meant to mimic the interface of set. Add missing functions as needed.
+	"""
+	def __init__(self, owner):
+		self._set = owner.run_after
+		self._owner = owner
+
+	def __iter__(self):
+		tasks = set(self._set) # make a copy
+		for g in self._owner.run_after_groups:
+			tasks.update(g)
+		for task in tasks:
+			yield task
+
+	def add(self, obj):
+		self._set.add(obj)
+
+	def update(self, obj):
+		self._set.update(obj)
+
+def set_precedence_constraints(tasks):
+	cstr_groups = Utils.defaultdict(list)
+	for x in tasks:
+		x.run_after = SetOfTasks(x)
+		x.run_after_groups = []
+
+		h = x.hash_constraints()
+		cstr_groups[h].append(x)
+
+	# create sets which can be reused for all tasks
+	for k in cstr_groups.iterkeys():
+		cstr_groups[k] = set(cstr_groups[k])
+
+	# this list should be short
+	for key1, key2 in itertools.combinations(cstr_groups.iterkeys(), 2):
+		group1 = cstr_groups[key1]
+		group2 = cstr_groups[key2]
+		# get the first entry of the set
+		t1 = iter(group1).next()
+		t2 = iter(group2).next()
+
+		# add the constraints based on the comparisons
+		if Task.is_before(t1, t2):
+			for x in group2:
+				x.run_after_groups.append(group1)
+		elif Task.is_before(t2, t1):
+			for x in group1:
+				x.run_after_groups.append(group2)
+
+Task.set_precedence_constraints = set_precedence_constraints
+