Import 'daemon' module

* https://github.com/serverdensity/python-daemon

src/vmpollerd/daemon.py

@@ -0,0 +1,211 @@
+'''
+***
+Modified generic daemon class
+***
+
+Author:         http://www.jejik.com/articles/2007/02/
+                        a_simple_unix_linux_daemon_in_python/www.boxedice.com
+
+License:        http://creativecommons.org/licenses/by-sa/3.0/
+
+Changes:        23rd Jan 2009 (David Mytton <[email protected]>)
+                - Replaced hard coded '/dev/null in __init__ with os.devnull
+                - Added OS check to conditionally remove code that doesn't
+                  work on OS X
+                - Added output to console on completion
+                - Tidied up formatting
+                11th Mar 2009 (David Mytton <[email protected]>)
+                - Fixed problem with daemon exiting on Python 2.4
+                  (before SystemExit was part of the Exception base)
+                13th Aug 2010 (David Mytton <[email protected]>
+                - Fixed unhandled exception if PID file is empty
+'''
+
+# Core modules
+import atexit
+import os
+import sys
+import time
+import signal
+
+
+class Daemon(object):
+    """
+    A generic daemon class.
+
+    Usage: subclass the Daemon class and override the run() method
+    """
+    def __init__(self, pidfile, stdin=os.devnull,
+                 stdout=os.devnull, stderr=os.devnull,
+                 home_dir='.', umask=022, verbose=1):
+        self.stdin = stdin
+        self.stdout = stdout
+        self.stderr = stderr
+        self.pidfile = pidfile
+        self.home_dir = home_dir
+        self.verbose = verbose
+        self.umask = umask
+        self.daemon_alive = True
+
+    def daemonize(self):
+        """
+        Do the UNIX double-fork magic, see Stevens' "Advanced
+        Programming in the UNIX Environment" for details (ISBN 0201563177)
+        http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16
+        """
+        try:
+            pid = os.fork()
+            if pid > 0:
+                # Exit first parent
+                sys.exit(0)
+        except OSError, e:
+            sys.stderr.write(
+                "fork #1 failed: %d (%s)\n" % (e.errno, e.strerror))
+            sys.exit(1)
+
+        # Decouple from parent environment
+        os.chdir(self.home_dir)
+        os.setsid()
+        os.umask(self.umask)
+
+        # Do second fork
+        try:
+            pid = os.fork()
+            if pid > 0:
+                # Exit from second parent
+                sys.exit(0)
+        except OSError, e:
+            sys.stderr.write(
+                "fork #2 failed: %d (%s)\n" % (e.errno, e.strerror))
+            sys.exit(1)
+
+        if sys.platform != 'darwin':  # This block breaks on OS X
+            # Redirect standard file descriptors
+            sys.stdout.flush()
+            sys.stderr.flush()
+            si = file(self.stdin, 'r')
+            so = file(self.stdout, 'a+')
+            if self.stderr:
+                se = file(self.stderr, 'a+', 0)
+            else:
+                se = so
+            os.dup2(si.fileno(), sys.stdin.fileno())
+            os.dup2(so.fileno(), sys.stdout.fileno())
+            os.dup2(se.fileno(), sys.stderr.fileno())
+
+        def sigtermhandler(signum, frame):
+            self.daemon_alive = False
+            signal.signal(signal.SIGTERM, sigtermhandler)
+            signal.signal(signal.SIGINT, sigtermhandler)
+
+        if self.verbose >= 1:
+            print "Started"
+
+        # Write pidfile
+        atexit.register(
+            self.delpid)  # Make sure pid file is removed if we quit
+        pid = str(os.getpid())
+        file(self.pidfile, 'w+').write("%s\n" % pid)
+
+    def delpid(self):
+        os.remove(self.pidfile)
+
+    def start(self, *args, **kwargs):
+        """
+        Start the daemon
+        """
+
+        if self.verbose >= 1:
+            print "Starting..."
+
+        # Check for a pidfile to see if the daemon already runs
+        try:
+            pf = file(self.pidfile, 'r')
+            pid = int(pf.read().strip())
+            pf.close()
+        except IOError:
+            pid = None
+        except SystemExit:
+            pid = None
+
+        if pid:
+            message = "pidfile %s already exists. Is it already running?\n"
+            sys.stderr.write(message % self.pidfile)
+            sys.exit(1)
+
+        # Start the daemon
+        self.daemonize()
+        self.run(*args, **kwargs)
+
+    def stop(self):
+        """
+        Stop the daemon
+        """
+
+        if self.verbose >= 1:
+            print "Stopping..."
+
+        # Get the pid from the pidfile
+        pid = self.get_pid()
+
+        if not pid:
+            message = "pidfile %s does not exist. Not running?\n"
+            sys.stderr.write(message % self.pidfile)
+
+            # Just to be sure. A ValueError might occur if the PID file is
+            # empty but does actually exist
+            if os.path.exists(self.pidfile):
+                os.remove(self.pidfile)
+
+            return  # Not an error in a restart
+
+        # Try killing the daemon process
+        try:
+            i = 0
+            while 1:
+                os.kill(pid, signal.SIGTERM)
+                time.sleep(0.1)
+                i = i + 1
+                if i % 10 == 0:
+                    os.kill(pid, signal.SIGHUP)
+        except OSError, err:
+            err = str(err)
+            if err.find("No such process") > 0:
+                if os.path.exists(self.pidfile):
+                    os.remove(self.pidfile)
+            else:
+                print str(err)
+                sys.exit(1)
+
+        if self.verbose >= 1:
+            print "Stopped"
+
+    def restart(self):
+        """
+        Restart the daemon
+        """
+        self.stop()
+        self.start()
+
+    def get_pid(self):
+        try:
+            pf = file(self.pidfile, 'r')
+            pid = int(pf.read().strip())
+            pf.close()
+        except IOError:
+            pid = None
+        except SystemExit:
+            pid = None
+        return pid
+
+    def is_running(self):
+        pid = self.get_pid()
+        print(pid)
+        return pid and os.path.exists('/proc/%d' % pid)
+
+    def run(self):
+        """
+        You should override this method when you subclass Daemon.
+        It will be called after the process has been
+        daemonized by start() or restart().
+        """