When scheduling builds in parallel for --jobs, avoid potential build dir

collisions in cases when the same exact cpv needs to be merged to multiple
$ROOTs (like when building stages). Thanks for Daniel Robbins for reporting
this issue and troubleshooting it.

svn path=/main/trunk/; revision=12557

1 files changed, 21 insertions, 0 deletions

diff --git a/pym/_emerge/__init__.py b/pym/_emerge/__init__.py
index 7f02a48d7..881ba9cc6 100644
--- a/pym/_emerge/__init__.py
+++ b/pym/_emerge/__init__.py
@@ -9937,6 +9937,7 @@ class Scheduler(PollScheduler):
 
 		self._digraph = digraph
 		self._prune_digraph()
+		self._prevent_builddir_collisions()
 
 	def _prune_digraph(self):
 		"""
@@ -9959,6 +9960,26 @@ class Scheduler(PollScheduler):
 				break
 			removed_nodes.clear()
 
+	def _prevent_builddir_collisions(self):
+		"""
+		When building stages, sometimes the same exact cpv needs to be merged
+		to both $ROOTs. Add edges to the digraph in order to avoid collisions
+		in the builddir. Currently, normal file locks would be inappropriate
+		for this purpose since emerge holds all of it's build dir locks from
+		the main process.
+		"""
+		cpv_map = {}
+		for pkg in self._mergelist:
+			if pkg.installed:
+				continue
+			if pkg.cpv not in cpv_map:
+				cpv_map[pkg.cpv] = [pkg]
+				continue
+			for earlier_pkg in cpv_map[pkg.cpv]:
+				self._digraph.add(earlier_pkg, pkg,
+					priority=DepPriority(buildtime=True))
+			cpv_map[pkg.cpv].append(pkg)
+
 	class _pkg_failure(portage.exception.PortageException):
 		"""
 		An instance of this class is raised by unmerge() when