python.SingleAppInstance.SingleAppInstance Class Reference

Inheritance diagram for python.SingleAppInstance.SingleAppInstance:

Collaboration diagram for python.SingleAppInstance.SingleAppInstance:

Classes
class	FileLockAcquisitionError
class	FileLockReleaseError

Public Member Functions
def	__init__ (self, path, debug=None, blocking=False)
def	acquire (self)
def	release (self)
def	islocked (self)
def	ownlock (self)
def	__del__ (self)
def	__enter__ (self)
def	__exit__ (self, typ, value, tb)

Public Attributes
	pid
	host
	path
	debug
	locked
	lockfile
	blocking

Static Public Attributes
string	addr = lambda self: '%d@%s' % (self.pid, self.host)
string	fddr = lambda self: '<%s %s>' % (self.path, self.addr())
string	pddr = lambda self, lock: '<%s %s@%s>' %\

Private Member Functions
def	_readlock (self)

Detailed Description

Class to handle creating and removing lockfiles

Definition at line 14 of file SingleAppInstance.py.

Constructor & Destructor Documentation

__init__()

def python.SingleAppInstance.SingleAppInstance.__init__	(		self,
			path,
			debug = None,
			blocking = False
	)

Definition at line 28 of file SingleAppInstance.py.

    def __init__(self, path, debug=None, blocking = False):
        self.pid   = os.getpid()
        self.host  = socket.gethostname()
        self.path  = path
        self.debug = debug # set this to get status messages
        self.locked = False
        self.lockfile = None
        self.blocking = blocking
  

__del__()

def python.SingleAppInstance.SingleAppInstance.__del__

(

self

)

Magic method to clean up lock when program exits

Definition at line 120 of file SingleAppInstance.py.

    def __del__(self):
        '''Magic method to clean up lock when program exits'''
        self.release()
 

Member Function Documentation

__enter__()

def python.SingleAppInstance.SingleAppInstance.__enter__

(

self

)

Definition at line 124 of file SingleAppInstance.py.

    def __enter__(self):
        self.acquire()
        return self
 

__exit__()

def python.SingleAppInstance.SingleAppInstance.__exit__	(		self,
			typ,
			value,
			tb
	)

Definition at line 128 of file SingleAppInstance.py.

    def __exit__(self, typ, value, tb):
        self.release()
        return self

_readlock()

def python.SingleAppInstance.SingleAppInstance._readlock (   self )

private

Internal method to read lock info

Definition at line 100 of file SingleAppInstance.py.

    def _readlock(self):
        '''Internal method to read lock info'''
        try:
            lock = {}
            fh   = open(self.path)
            data = fh.read().rstrip().split('@')
            fh.close()
            lock['pid'], lock['host'] = data
            return lock
        except Exception:
            return {'pid': 8**10, 'host': ''}
        

acquire()

def python.SingleAppInstance.SingleAppInstance.acquire

(

self

)

Acquire a lock, returning self if successful, False otherwise

Definition at line 37 of file SingleAppInstance.py.

    def acquire(self):
        '''Acquire a lock, returning self if successful, False otherwise'''
        if self.islocked():
            if self.debug:
                lock = self._readlock()
                print('Previous lock detected: %s' % self.pddr(lock))
            return False
        try:
            fd = os.open(self.path, os.O_RDWR | os.O_CREAT, 0o777)
            fh = os.fdopen(fd, 'r+')
            self.lockfile = fh
            fh.seek(0)
            try:
                fcntlflag = fcntl.LOCK_EX
                if not self.blocking:
                    fcntlflag |= fcntl.LOCK_NB
                    fcntl.lockf(fh, fcntlflag)
                    self.locked = True
            except IOError:
                print('Unable to acquire lock on %s: existing lock %s' % (self.path, fh.read()))
                fh.close()
                return False
            fh.write(self.addr())
            fh.truncate()
            fh.flush()
            os.fsync(fh)
            if self.debug:
                modtime = os.stat(self.path)
                outstring = 'Acquired lock: '+ self.fddr() + ' at time '+ time.ctime(modtime.st_mtime)
                print(outstring)
        except Exception as e:
            if os.path.isfile(self.path):
                try:
                    # my guess is this causes problems
                    #os.unlink(self.path)
                    pass
                except Exception:
                    pass
            raise self.FileLockAcquisitionError(
              'Error acquiring lock: %s, reason %s' % (self.fddr(), e))
        return self
  

islocked()

def python.SingleAppInstance.SingleAppInstance.islocked

(

self

)

Check if we already have a lock

Definition at line 112 of file SingleAppInstance.py.

    def islocked(self):
        '''Check if we already have a lock'''
        return self.locked
  

ownlock()

def python.SingleAppInstance.SingleAppInstance.ownlock

(

self

)

Check if we own the lock

Definition at line 116 of file SingleAppInstance.py.

    def ownlock(self):
        '''Check if we own the lock'''
        return self.locked
  

release()

def python.SingleAppInstance.SingleAppInstance.release

(

self

)

Release lock, returning self

Definition at line 79 of file SingleAppInstance.py.

    def release(self):
        '''Release lock, returning self'''
        if self.ownlock():
            try:
                fh = self.lockfile
                fcntl.lockf(fh, fcntl.LOCK_UN)
                self.locked = False
                self.lockfile.close()
                self.lockfile = None
                if not self.blocking:
                    # some space for a small race here unfortunately
                    os.unlink(self.path)
                if self.debug:
                    outstring  = 'Released lock: ' + self.fddr() +' at time ' +  time.ctime()
                    print(outstring)
            except Exception as e:
                print(e)
                raise self.FileLockReleaseError(
                  'Error releasing lock: %s, reason %s' % (self.fddr(), e))
        return self
  

Member Data Documentation

addr

string python.SingleAppInstance.SingleAppInstance.addr = lambda self: '%d@%s' % (self.pid, self.host)

static

Definition at line 23 of file SingleAppInstance.py.

blocking

python.SingleAppInstance.SingleAppInstance.blocking

Definition at line 35 of file SingleAppInstance.py.

debug

python.SingleAppInstance.SingleAppInstance.debug

Definition at line 32 of file SingleAppInstance.py.

fddr

string python.SingleAppInstance.SingleAppInstance.fddr = lambda self: '<%s %s>' % (self.path, self.addr())

static

Definition at line 24 of file SingleAppInstance.py.

host

python.SingleAppInstance.SingleAppInstance.host

Definition at line 30 of file SingleAppInstance.py.

locked

python.SingleAppInstance.SingleAppInstance.locked

Definition at line 33 of file SingleAppInstance.py.

lockfile

python.SingleAppInstance.SingleAppInstance.lockfile

Definition at line 34 of file SingleAppInstance.py.

path

python.SingleAppInstance.SingleAppInstance.path

Definition at line 31 of file SingleAppInstance.py.

pddr

string python.SingleAppInstance.SingleAppInstance.pddr = lambda self, lock: '<%s %s@%s>' %\

static

Definition at line 25 of file SingleAppInstance.py.

pid

python.SingleAppInstance.SingleAppInstance.pid

Definition at line 29 of file SingleAppInstance.py.

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The documentation for this class was generated from the following file:

• SingleAppInstance.py