ebuild-ipc: use non-blocking read

This makes it possible for the daemon to send a reply without blocking,
thereby improving performance and also making it possible for the
daemon to do a non-blocking write without a race condition.

This reverts part of commit 81fc303212b8379219cf5d463c8717359b972dba,
which probably didn't help portability anyway. Now, ebuild-ipc is using
non-blocking read with os.read and EAGAIN handling, just like
EbuildIpcDaemon since commit 7e5b81da12dd7bd59f6620840dc0d824e3f4d69a
(known compatible with FreeBSD).

1 files changed, 41 insertions, 13 deletions

diff --git a/bin/ebuild-ipc.py b/bin/ebuild-ipc.py
index d8e7e5512..cb77171ec 100755
--- a/bin/ebuild-ipc.py
+++ b/bin/ebuild-ipc.py
@@ -134,23 +134,43 @@ class EbuildIpc(object):
 
 		return os.WEXITSTATUS(wait_retval[1])
 
-	def _receive_reply(self):
+	def _receive_reply(self, input_fd):
 
-		# File streams are in unbuffered mode since we do atomic
-		# read and write of whole pickles.
-		input_file = open(self.ipc_out_fifo, 'rb', 0)
-
-		# For maximum portability, use a single atomic read.
+		# Timeouts are handled by the parent process, so just
+		# block until input is available. For maximum portability,
+		# use a single atomic read.
 		buf = None
-		try:
-			buf = input_file.read(self._BUFSIZE)
-		except IOError as e:
-			if not buf:
+		while True:
+			try:
+				events = select.select([input_fd], [], [])
+			except select.error as e:
 				portage.util.writemsg_level(
-					"ebuild-ipc: %s\n" % (e,),
+					"ebuild-ipc: %s: %s\n" % \
+					(portage.localization._('during select for read'), e),
 					level=logging.ERROR, noiselevel=-1)
+				continue
 
-		input_file.close()
+			if events[0]:
+				# For maximum portability, use os.read() here since
+				# array.fromfile() and file.read() are both known to
+				# erroneously return an empty string from this
+				# non-blocking fifo stream on FreeBSD (bug #337465).
+				try:
+					buf = os.read(input_fd, self._BUFSIZE)
+				except OSError as e:
+					if e.errno != errno.EAGAIN:
+						portage.util.writemsg_level(
+							"ebuild-ipc: %s: %s\n" % \
+							(portage.localization._('read error'), e),
+							level=logging.ERROR, noiselevel=-1)
+						break
+					# Assume that another event will be generated
+					# if there's any relevant data.
+					continue
+
+				# Only one (atomic) read should be necessary.
+				if buf:
+					break
 
 		retval = 2
 
@@ -192,6 +212,13 @@ class EbuildIpc(object):
 			self._no_daemon_msg()
 			return 2
 
+		# Open the input fifo before the output fifo, in order to make it
+		# possible for the daemon to send a reply without blocking. This
+		# improves performance, and also makes it possible for the daemon
+		# to do a non-blocking write without a race condition.
+		input_fd = os.open(self.ipc_out_fifo,
+			os.O_RDONLY|os.O_NONBLOCK)
+
 		# Use forks so that the child process can handle blocking IO
 		# un-interrupted, while the parent handles all timeout
 		# considerations. This helps to avoid possible race conditions
@@ -231,12 +258,13 @@ class EbuildIpc(object):
 
 		if pid == 0:
 			os.close(pr)
-			retval = self._receive_reply()
+			retval = self._receive_reply(input_fd)
 			os._exit(retval)
 
 		os.close(pw)
 		retval = self._wait(pid, pr, portage.localization._('during read'))
 		os.close(pr)
+		os.close(input_fd)
 		return retval
 
 def ebuild_ipc_main(args):