Python - python-daemon lockfile timeout on lock.aquire()

Question

I am using python-daemon module to manage the daemon process of my Python script. However, I am running into a headache when running the script that I simply can't figure out. Nor do I really know how to begin to debug it.

I have the code:

def run_application():
    #Do something here...

class App():
    def __init__(self):
        self.stdin_path = '/dev/null'
        self.stdout_path = 'stdout.txt'
        self.stderr_path = 'stdlog.log'
        self.pidfile_path = 'filelock.pid'
        self.pidfile_timeout = 5
    def run(self):
        run_application()


app = App()
daemon_runner = runner.DaemonRunner(app)
daemon_runner.do_action()

When run, it always writes the following to stdlog.log:

Traceback (most recent call last):
  File "MyApp.py", line 335, in <module>
    daemon_runner.do_action()
  File "/anaconda/lib/python2.7/site-packages/daemon/runner.py", line 189, in do_action
    func(self)
  File "/anaconda/lib/python2.7/site-packages/daemon/runner.py", line 124, in _start
    self.daemon_context.open()
  File "/anaconda/lib/python2.7/site-packages/daemon/daemon.py", line 346, in open
    self.pidfile.__enter__()
  File "/anaconda/lib/python2.7/site-packages/lockfile/__init__.py", line 229, in __enter__
    self.acquire()
  File "/anaconda/lib/python2.7/site-packages/daemon/pidfile.py", line 42, in acquire
    super(TimeoutPIDLockFile, self).acquire(timeout, *args, **kwargs)
  File "/anaconda/lib/python2.7/site-packages/lockfile/pidlockfile.py", line 88, in acquire
    self.path)
lockfile.LockTimeout: Timeout waiting to acquire lock for /MyApp/filelock.pid

So it appears to be timing out when attempting to lock filelock.pid. I have no idea why this is. I have deleted filelock.pid, I've changed permissions; same error every time.

How can I begin to debug this??? I'm at a loss.

I am using python-daemon version 1.6 (if it matters).

Update:

Following the advice here, I now see that there is already a process running. Now how can I figure out how to determine the PID of the running daemon process.

Answer 1

I agree with @ExploWare as far as how he demonstrates you can capture those LockTimeout exceptions.

So as far as a way to debug and see what process is holding on to this lock, here is an external bit of code you can run...

import daemon.pidfile
import os
import lockfile

# We know the lockfile name.
pidfile = daemon.pidfile.PIDLockFile(
                            os.path.join("/MyApp/","filelock.pid"))

# This current process id...
os.getpid()
# 46337

So what process has acquired this lock if any?

pidfile.is_locked()
# True

pidfile.read_pid()
# 96856

When our PIDLockFile instance tries to "acquire",

pidfile.__dict__
# {'unique_name': '/MyApp/filelock.pid', 'lock_file': '/MyApp/filelock.pid.lock', 'hostname': 
# 'MyMachine.local', 'pid': 46337, 'timeout': None, 'tname': '', 'path': '/MyApp/filelock.pid'}

pidfile.acquire()
#
# (Had to Control-C quit because I didnt set a timeout on PIDLockFile )
#
# ^CTraceback (most recent call last):
#   File "<stdin>", line 1, in <module>
#   File "/Users/michal/venf/lib/python2.7/site-packages/lockfile/pidlockfile.py", line 92, in acquire
#     time.sleep(timeout is not None and timeout/10 or 0.1)
# KeyboardInterrupt

So instead, use @ExploWare 's exception catching.

# Wait only 5 seconds.
pidfile.timeout = 5

try:
    pidfile.acquire()
except lockfile.LockTimeout:
    print 'locked . need to wait or move on.'
# 
# locked . need to wait or move on.