[gentoo-commits] proj/portage:master commit in: pym/_emerge/

["Zac Medico" <zmedico@gentoo.org>]

commit:     b3bba4dc8f4f93adeaeaf662870bb00a09bb1de7
Author:     Zac Medico <zmedico <AT> gentoo <DOT> org>
AuthorDate: Fri Dec 26 08:59:58 2014 +0000
Commit:     Zac Medico <zmedico <AT> gentoo <DOT> org>
CommitDate: Mon Jan  5 19:31:48 2015 +0000
URL:        http://sources.gentoo.org/gitweb/?p=proj/portage.git;a=commit;h=b3bba4dc

AbstractPollTask._read_buf: read regardless of event flags (531724)

PipeReaderPtyTestCase shows that data may be lost unless we attempt to
read data for every poll event, regardless of the event flags.

Therefore, always read, regardless of the event flags. This is safe to
do because all consumers of this API use non-blocking mode and properly
handle EAGAIN (signaled when this method returns None).

X-Gentoo-Bug: 531724
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=531724
Acked-by: Alexander Berntsen <bernalex <AT> gentoo.org>

---
 pym/_emerge/AbstractPollTask.py | 52 +++++++++++++++++++++++------------------
 1 file changed, 29 insertions(+), 23 deletions(-)

diff --git a/pym/_emerge/AbstractPollTask.py b/pym/_emerge/AbstractPollTask.py
index 3f6dd6c..0d38bd4 100644
--- a/pym/_emerge/AbstractPollTask.py
+++ b/pym/_emerge/AbstractPollTask.py
@@ -1,4 +1,4 @@
-# Copyright 1999-2012 Gentoo Foundation
+# Copyright 1999-2015 Gentoo Foundation
 # Distributed under the terms of the GNU General Public License v2
 
 import array
@@ -78,33 +78,39 @@ class AbstractPollTask(AsynchronousTask):
 
 	def _read_buf(self, fd, event):
 		"""
-		| POLLIN | RETURN
-		| BIT    | VALUE
-		| ---------------------------------------------------
-		| 1      | Read self._bufsize into a string of bytes,
-		|        | handling EAGAIN and EIO. An empty string
-		|        | of bytes indicates EOF.
-		| ---------------------------------------------------
-		| 0      | None
+		Read self._bufsize into a string of bytes, handling EAGAIN and
+		EIO. This will only call os.read() once, so the caller should
+		call this method in a loop until either None or an empty string
+		of bytes is returned. An empty string of bytes indicates EOF.
+		None indicates EAGAIN.
+
+		NOTE: os.read() will be called regardless of the event flags,
+			since otherwise data may be lost (see bug #531724).
+
+		@param fd: file descriptor (non-blocking mode required)
+		@type fd: int
+		@param event: poll event flags
+		@type event: int
+		@rtype: bytes or None
+		@return: A string of bytes, or None
 		"""
 		# NOTE: array.fromfile() is no longer used here because it has
 		# bugs in all known versions of Python (including Python 2.7
 		# and Python 3.2).
 		buf = None
-		if event & self.scheduler.IO_IN:
-			try:
-				buf = os.read(fd, self._bufsize)
-			except OSError as e:
-				# EIO happens with pty on Linux after the
-				# slave end of the pty has been closed.
-				if e.errno == errno.EIO:
-					# EOF: return empty string of bytes
-					buf = b''
-				elif e.errno == errno.EAGAIN:
-					# EAGAIN: return None
-					buf = None
-				else:
-					raise
+		try:
+			buf = os.read(fd, self._bufsize)
+		except OSError as e:
+			# EIO happens with pty on Linux after the
+			# slave end of the pty has been closed.
+			if e.errno == errno.EIO:
+				# EOF: return empty string of bytes
+				buf = b''
+			elif e.errno == errno.EAGAIN:
+				# EAGAIN: return None
+				buf = None
+			else:
+				raise
 
 		return buf