From 58b184b441ff53c46cbb38eb695933d60c6624ad Mon Sep 17 00:00:00 2001
From: Zac Medico <zmedico@gentoo.org>
Date: Mon, 13 Sep 2010 00:23:34 -0700
Subject: [PATCH] Bug #336142 - Add support for using a thread to wait for
 locks inside dblink.lockdb() so that the scheduler can concurrently service
 ipc calls in the main thread.

---
 pym/portage/dbapi/vartree.py | 34 ++++++++++++++++++++++++++++++++--
 pym/portage/locks.py         |  4 ++--
 2 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/pym/portage/dbapi/vartree.py b/pym/portage/dbapi/vartree.py
index fddb4326c..19ebaaa76 100644
--- a/pym/portage/dbapi/vartree.py
+++ b/pym/portage/dbapi/vartree.py
@@ -37,7 +37,7 @@ from portage.const import _ENABLE_DYN_LINK_MAP, _ENABLE_PRESERVE_LIBS
 from portage.dbapi import dbapi
 from portage.exception import CommandNotFound, \
 	InvalidData, InvalidPackageName, \
-	FileNotFound, PermissionDenied, UnsupportedAPIException
+	FileNotFound, PermissionDenied, TryAgain, UnsupportedAPIException
 from portage.localization import _
 from portage.util.movefile import movefile
 
@@ -62,6 +62,10 @@ import os as _os
 import stat
 import sys
 import tempfile
+try:
+	import threading
+except ImportError:
+	import dummy_threading as threading
 import time
 import warnings
 
@@ -1276,13 +1280,39 @@ class dblink(object):
 			raise AssertionError("Lock already held.")
 		# At least the parent needs to exist for the lock file.
 		ensure_dirs(self.dbroot)
-		self._lock_vdb = lockdir(self.dbroot)
+		if self._scheduler is None:
+			self._lock_vdb = lockdir(self.dbroot)
+		else:
+			try:
+				self._lock_vdb = lockdir(self.dbroot, flags=os.O_NONBLOCK)
+			except TryAgain:
+				self._lockdb_rlock = threading.RLock()
+				lockdb_thread = threading.Thread(
+					target=self._lockdb_thread)
+				lockdb_thread.start()
+				if not self._lockdb_have_lock():
+					self._scheduler.schedule(
+						condition=self._lockdb_have_lock)
+				lockdb_thread.join()
+				self._lockdb_rlock = None
 
 	def unlockdb(self):
 		if self._lock_vdb:
 			unlockdir(self._lock_vdb)
 			self._lock_vdb = None
 
+	def _lockdb_thread(self):
+		lock_vdb = lockdir(self.dbroot)
+		self._lockdb_rlock.acquire()
+		self._lock_vdb = lock_vdb
+		self._lockdb_rlock.release()
+
+	def _lockdb_have_lock(self):
+		self._lockdb_rlock.acquire()
+		rval = self._lock_vdb is not None
+		self._lockdb_rlock.release()
+		return rval
+
 	def getpath(self):
 		"return path to location of db information (for >>> informational display)"
 		return self.dbdir
diff --git a/pym/portage/locks.py b/pym/portage/locks.py
index ed20e30ca..00a50b818 100644
--- a/pym/portage/locks.py
+++ b/pym/portage/locks.py
@@ -30,8 +30,8 @@ HARDLINK_FD = -2
 # so that it doesn't interfere with the status display.
 _quiet = False
 
-def lockdir(mydir):
-	return lockfile(mydir,wantnewlockfile=1)
+def lockdir(mydir, flags=0):
+	return lockfile(mydir, wantnewlockfile=1, flags=flags)
 def unlockdir(mylock):
 	return unlockfile(mylock)
 
-- 
2.26.2