Add submanager script.

This script allow to run a command and restart it
it if some files changes.

The submanager catch SIGUSR1 and checks if the specified
files has changed.

It can use a pid file where its own pid is written.

This is usefull for restarting a service from a recipe.

Example :
  submanager -c config.cfg -- command --with-options -y
    Run “command --with-options -y” and restart it if
    config.cfg is modified after receiving SIGUSR

slapos/submanager.py

+##############################################################################
+#
+# Copyright (c) 2010 Vifib SARL and Contributors. All Rights Reserved.
+#
+# WARNING: This program as such is intended to be used by professional
+# programmers who take the whole responsibility of assessing all potential
+# consequences resulting from its eventual inadequacies and bugs
+# End users who are looking for a ready-to-use solution with commercial
+# guarantees and support are strongly adviced to contract a Free Software
+# Service Company
+#
+# 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 3
+# 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., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
+#
+##############################################################################
+import argparse
+import hashlib
+import os
+import signal
+import shutil
+import subprocess
+
+PROCESS = None
+
+class HashFile(object):
+
+  def __init__(self, hash_name):
+    if hash_name not in hashlib.algorithms:
+      raise ValueError("hash_name is not valid.")
+    self._hash = getattr(hashlib, hash_name)()
+
+  def close(self):
+    pass
+
+  def digest(self):
+    return self._hash.digest()
+
+  def flush(self):
+    pass
+
+  def fileno(self):
+    raise NotImplementedError("fileno() not implemented on HashFiles")
+
+  def hexdigest(self):
+    return self._hash.hexdigest()
+
+  def isatty(self):
+    return False
+
+  def next(self):
+    raise NotImplementedError("next() not implemented on HashFiles")
+
+  def read(self, size=None):
+    raise NotImplementedError("read() not implemented on HashFiles")
+
+  def readlines(self, size=None):
+    raise NotImplementedError("readlines() not implemented on HashFiles")
+
+  def tell(self):
+    return self._position
+
+  def truncate(self, size=None):
+    raise NotImplementedError("truncate([size]) not implemented on HashFiles")
+
+  def write(self, string):
+    self._hash.update(string)
+
+  def writelines(self, sequence):
+    for line in sequence:
+      self.write('%s\n' % line)
+
+
+
+class Process(object):
+
+  def __init__(self, command_line, files):
+    self.restarting = True
+
+    self.command_line = command_line
+    self.files = dict()
+    for filename in files:
+      if not os.path.exists(filename):
+        raise OSError("%s does not exist" % filename)
+      self.files[filename] = self.sha512sum(filename)
+
+    self._subprocess = subprocess.Popen(self.command_line)
+    self.restarting = False
+
+  def sha512sum(self, filename):
+    hash_ = HashFile('sha512')
+    with open(filename, 'r') as file_:
+      shutil.copyfileobj(file_, hash_)
+    return hash_.digest()
+
+  def mainloop(self):
+    while self._subprocess.poll() is None:
+      signal.pause()
+    return self._subprocess.returncode
+
+  def terminate(self):
+    if self._subprocess.poll() is None:
+      self._subprocess.terminate()
+
+  def restart(self):
+    self.restarting = True
+    modified = False
+    for filename, checksum in self.files.iteritems():
+      if not os.path.exists(filename):
+        raise OSError("%s does not exist" % filename)
+      new_checksum = self.sha512sum(filename)
+      if new_checksum != checksum:
+        modified = True
+      self.files[filename] = new_checksum
+
+    if modified:
+      self._subprocess.terminate()
+      self._subprocess.wait()
+      self._subprocess = subprocess.Popen(self.command_line)
+    self.restarting = False
+
+
+def usr1_handler(signum, frame):
+  global PROCESS
+
+  if PROCESS.restarting is False:
+    PROCESS.restart()
+
+def main():
+  global PROCESS
+
+  parser = argparse.ArgumentParser(
+    description="Manager catching SIGUSR1 and reloading application "
+                "according if configuration files changed"
+  )
+  parser.add_argument('-c', '--config', action='append', required=True,
+                      help='Configuration file, multiple values')
+  parser.add_argument('-p', '--pidfile', action='store', required=False,
+                      help='Create a PID file')
+  parser.add_argument('argument', nargs='+', help='Command line argument')
+
+  args = parser.parse_args()
+
+  if args.pidfile is not None:
+    with open(args.pidfile, 'w') as pid_file:
+      pid_file.write('%d' % os.getpid())
+
+  PROCESS = Process(args.argument, args.config)
+  signal.signal(signal.SIGUSR1, usr1_handler)
+  try:
+    return PROCESS.mainloop()
+  finally:
+    PROCESS.terminate()
+    if args.pidfile is not None and os.path.exists(args.pidfile):
+      os.unlink(args.pidfile)
+
+if __name__ == '__main__':
+  import sys
+  sys.exit(main())