Add daemon library with mainloop

This mainloop can be used in daemons like ganeti-noded.

Reviewed-by: iustinp

Makefile.am

@@ -66,6 +66,7 @@ pkgpython_PYTHON = \
 	lib/cmdlib.py \
 	lib/config.py \
 	lib/constants.py \
+	lib/daemon.py \
 	lib/errors.py \
 	lib/http.py \
 	lib/jqueue.py \

lib/daemon.py

+#
+#
+
+# Copyright (C) 2006, 2007, 2008 Google Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301, USA.
+
+
+"""Module with helper classes and functions for daemons"""
+
+
+import select
+import signal
+import errno
+
+from ganeti import utils
+
+
+class Mainloop(object):
+  """Generic mainloop for daemons
+
+  """
+  def __init__(self):
+    self._io_wait = []
+    self._signal_wait = []
+    self.sigchld_handler = {}
+
+  def Run(self):
+    # TODO: Does not yet support adding new event sources while running
+    poller = select.poll()
+    for (owner, fd, conditions) in self._io_wait:
+      poller.register(fd, conditions)
+
+    self.sigchld_handler = utils.SignalHandler([signal.SIGCHLD])
+    try:
+      while True:
+        try:
+          io_events = poller.poll(1000)
+        except select.error, err:
+          # EINTR can happen when signals are sent
+          if err.args and err.args[0] in (errno.EINTR,):
+            io_events = None
+          else:
+            raise
+
+        if io_events:
+          # Check for I/O events
+          for (evfd, evcond) in io_events:
+            for (owner, fd, conditions) in self._io_wait:
+              if fd == evfd and evcond & conditions:
+                owner.OnIO(fd, evcond)
+
+        # Check whether signal was raised
+        if self.sigchld_handler.called:
+          for owner in self._signal_wait:
+            owner.OnSignal(signal.SIGCHLD)
+          self.sigchld_handler.Clear()
+    finally:
+      self.sigchld_handler.Reset()
+      self.sigchld_handler = None
+
+  def RegisterIO(self, owner, fd, condition):
+    """Registers a receiver for I/O notifications
+
+    The receiver must support a "OnIO(self, fd, conditions)" function.
+
+    @type owner: instance
+    @param owner: Receiver
+    @type fd: int
+    @param fd: File descriptor
+    @type condition: int
+    @param condition: ORed field of conditions to be notified
+                      (see select module)
+
+    """
+    self._io_wait.append((owner, fd, condition))
+
+  def RegisterSignal(self, owner):
+    """Registers a receiver for signal notifications
+
+    The receiver must support a "OnSignal(self, signum)" function.
+
+    @type owner: instance
+    @param owner: Receiver
+
+    """
+    self._signal_wait.append(owner)