--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/pylons_app/lib/indexers/pidlock.py	Tue Aug 17 23:15:36 2010 +0200
@@ -0,0 +1,127 @@
+import os, time
+import sys
+from warnings import warn
+
+class LockHeld(Exception):pass
+
+
+class DaemonLock(object):
+    '''daemon locking
+    USAGE:
+    try:
+        l = lock()
+        main()
+        l.release()
+    except LockHeld:
+        sys.exit(1)
+    '''
+
+    def __init__(self, file=None, callbackfn=None,
+                 desc='daemon lock', debug=False):
+
+        self.pidfile = file if file else os.path.join(os.path.dirname(__file__),
+                                                      'running.lock')
+        self.callbackfn = callbackfn
+        self.desc = desc
+        self.debug = debug
+        self.held = False
+        #run the lock automatically !
+        self.lock()
+
+    def __del__(self):
+        if self.held:
+
+#            warn("use lock.release instead of del lock",
+#                    category = DeprecationWarning,
+#                    stacklevel = 2)
+
+            # ensure the lock will be removed
+            self.release()
+
+
+    def lock(self):
+        '''
+        locking function, if lock is present it will raise LockHeld exception
+        '''
+        lockname = '%s' % (os.getpid())
+
+        self.trylock()
+        self.makelock(lockname, self.pidfile)
+        return True
+
+    def trylock(self):
+        running_pid = False
+        try:
+            pidfile = open(self.pidfile, "r")
+            pidfile.seek(0)
+            running_pid = pidfile.readline()
+            if self.debug:
+                print 'lock file present running_pid: %s, checking for execution'\
+                % running_pid
+            # Now we check the PID from lock file matches to the current
+            # process PID
+            if running_pid:
+                if os.path.exists("/proc/%s" % running_pid):
+                        print "You already have an instance of the program running"
+                        print "It is running as process %s" % running_pid
+                        raise LockHeld
+                else:
+                        print "Lock File is there but the program is not running"
+                        print "Removing lock file for the: %s" % running_pid
+                        self.release()
+        except IOError, e:
+            if e.errno != 2:
+                raise
+
+
+    def release(self):
+        '''
+        releases the pid by removing the pidfile
+        '''
+        if self.callbackfn:
+            #execute callback function on release
+            if self.debug:
+                print 'executing callback function %s' % self.callbackfn
+            self.callbackfn()
+        try:
+            if self.debug:
+                print 'removing pidfile %s' % self.pidfile
+            os.remove(self.pidfile)
+            self.held = False
+        except OSError, e:
+            if self.debug:
+                print 'removing pidfile failed %s' % e
+            pass
+
+    def makelock(self, lockname, pidfile):
+        '''
+        this function will make an actual lock
+        @param lockname: acctual pid of file
+        @param pidfile: the file to write the pid in
+        '''
+        if self.debug:
+            print 'creating a file %s and pid: %s' % (pidfile, lockname)
+        pidfile = open(self.pidfile, "wb")
+        pidfile.write(lockname)
+        pidfile.close
+        self.held = True
+
+
+def main():
+    print 'func is running'
+    cnt = 20
+    while 1:
+        print cnt
+        if cnt == 0:
+            break
+        time.sleep(1)
+        cnt -= 1
+
+
+if __name__ == "__main__":
+    try:
+        l = DaemonLock(desc='test lock')
+        main()
+        l.release()
+    except LockHeld:
+        sys.exit(1)