EbuildIpcDaemon: handle POLLHUP, bug #401919

diff --git a/pym/_emerge/EbuildIpcDaemon.py b/pym/_emerge/EbuildIpcDaemon.py
index 5795bfbdcd115a4ad1c961fbad40cbc6fcd6c32f..8414d202028f10dc1b97eb5de821e1e34c7a2da6 100644 (file)
--- a/pym/_emerge/EbuildIpcDaemon.py
+++ b/pym/_emerge/EbuildIpcDaemon.py
@@ -5,7 +5,9 @@ import errno
 import logging
 import pickle
 from portage import os
+from portage.exception import TryAgain
 from portage.localization import _
+from portage.locks import lockfile, unlockfile
 from portage.util import writemsg_level
 from _emerge.FifoIpcDaemon import FifoIpcDaemon
 
@@ -83,6 +85,28 @@ class EbuildIpcDaemon(FifoIpcDaemon):
                                if reply_hook is not None:
                                        reply_hook()
 
+               elif event & self.scheduler.IO_HUP:
+                       # This can be triggered due to a race condition which happens when
+                       # the previous _reopen_input() call occurs before the writer has
+                       # closed the pipe (see bug #401919). It's not safe to re-open
+                       # without a lock here, since it's possible that another writer will
+                       # write something to the pipe just before we close it, and in that
+                       # case the write will be lost. Therefore, try for a non-blocking
+                       # lock, and only re-open the pipe if the lock is acquired.
+                       lock_filename = os.path.join(
+                               os.path.dirname(self.input_fifo), '.ipc_lock')
+                       try:
+                               lock_obj = lockfile(lock_filename, unlinkfile=True,
+                                       flags=os.O_NONBLOCK)
+                       except TryAgain:
+                               # We'll try again when another IO_HUP event arrives.
+                               pass
+                       else:
+                               try:
+                                       self._reopen_input()
+                               finally:
+                                       unlockfile(lock_obj)
+
                return True
 
        def _send_reply(self, reply):