EbuildIpcDaemon: use non-blocking write

This prevents the Scheduler from hanging if the client is killed before
we can send the reply, as reported by David James:

  http://codereview.chromium.org/6713003

This commit depends on ebuild-ipc (the client) opening the other side
of this fifo before it sends its request, which has already been added
in commit eff879ff0ce7dcc1ce68d5f16de1ec73051f8c18.

1 files changed, 24 insertions, 5 deletions

diff --git a/pym/_emerge/EbuildIpcDaemon.py b/pym/_emerge/EbuildIpcDaemon.py
index efcda9316..5dabe34b3 100644
--- a/pym/_emerge/EbuildIpcDaemon.py
+++ b/pym/_emerge/EbuildIpcDaemon.py
@@ -1,9 +1,12 @@
-# Copyright 2010 Gentoo Foundation
+# Copyright 2010-2011 Gentoo Foundation
 # Distributed under the terms of the GNU General Public License v2
 
 import errno
+import logging
 import pickle
 from portage import os
+from portage.localization import _
+from portage.util import writemsg_level
 from _emerge.FifoIpcDaemon import FifoIpcDaemon
 from _emerge.PollConstants import PollConstants
 
@@ -83,7 +86,23 @@ class EbuildIpcDaemon(FifoIpcDaemon):
 
 	def _send_reply(self, reply):
 		# File streams are in unbuffered mode since we do atomic
-		# read and write of whole pickles.
-		output_file = open(self.output_fifo, 'wb', 0)
-		output_file.write(pickle.dumps(reply))
-		output_file.close()
+		# read and write of whole pickles. Use non-blocking mode so
+		# we don't hang if the client is killed before we can send
+		# the reply. We rely on the client opening the other side
+		# of this fifo before it sends its request, since otherwise
+		# we'd have a race condition with this open call raising
+		# ENXIO if the client hasn't opened the fifo yet.
+		try:
+			output_fd = os.open(self.output_fifo,
+				os.O_WRONLY | os.O_NONBLOCK)
+			try:
+				os.write(output_fd, pickle.dumps(reply))
+			finally:
+				os.close(output_fd)
+		except OSError as e:
+			# This probably means that the client has been killed,
+			# which causes open to fail with ENXIO.
+			writemsg_level(
+				"!!! EbuildIpcDaemon %s: %s\n" % \
+				(_('failed to send reply'), e),
+				level=logging.ERROR, noiselevel=-1)