lockfile.py

import subprocess
import os
import socket
import datetime


class LockFile(object):

    def __init__(self, lockfile_type):

        hostname = socket.gethostname()
        self._lockfile_name = f"Lockfile.{lockfile_type}.{hostname}"
        self._tmp_lockfile_name = f"/tmp/Lockfile.{lockfile_type}.{hostname}"
        self._process_ids = []

    def log(self, msg):

        f = None
        x = datetime.datetime.now()

        try:
            f = open(self._tmp_lockfile_name, "a")
            f.write(f'{x.strftime("%Y-%m-%d:%H:%M:%S")}: {msg}\n')
        finally:
            if f:
                f.close()

    def run_ps(self):

        # this only works in python2.7
        # print "running ps"
        self.log("Getting list of system PIDs ...")
        x = subprocess.check_output(['ps', 'aux'], stderr=subprocess.STDOUT)
        lines = x.split('\n')
        for line in lines:
            if not line:
                continue
            # print "LINE", line
            parts = line.split()
            # print parts
            if parts[0] == 'USER':
                continue
            self._process_ids.append(int(parts[1]))

        self.log(f"Read {len(self._process_ids)} system PIDs")

    def get_lock_pid(self):

        result = None
        try:
            f = open(self._lockfile_name)
            if f:
                for line in f:
                    if line:
                        result = int(line)
                f.close()
        except Exception:
            result = None

        self.log("get_lock_pid({self._lockfile_name}): returning: {repr(result)}")
        return result

    def set_lock_pid(self, my_pid):

        f = open(self._lockfile_name, "w")
        f.write("%d\n" % my_pid)
        f.close()

    def acquire(self):

        pid = self.get_lock_pid()

        if pid is None:
            self.log("No lockfile found")
            my_pid = int(os.getpid())
            self.set_lock_pid(my_pid)
            pid = self.get_lock_pid()
            if my_pid == pid:
                self.log("Created new lockfile with PID: %d; starting" % my_pid)
                return

            self.log("Failed to create new lockfile with PID: %d; not starting" % my_pid)
            raise ValueError("Failed to create lockfile: %s: %d != %d; not starting" % (self._lockfile_name, my_pid, pid))

        self.log("Found existing PID: %d" % pid)
        self.run_ps()

        if pid in self._process_ids:
            self.log("Lockfile PID %d in list of running PIDs; not starting" % pid)
            raise ValueError("Detected process with PID: %d (%s)" % (pid, self._lockfile_name))

        self.log("removing stale lockfile for PID: %d" % pid)
        os.remove(self._lockfile_name)

        my_pid = int(os.getpid())
        self.set_lock_pid(my_pid)
        pid = self.get_lock_pid()
        if my_pid == pid:
            self.log("Created new lockfile with PID: %d; starting" % my_pid)
            return

        self.log("Failed to create new lockfile with PID: %d; not starting" % my_pid)
        raise ValueError("Failed to create lockfile: %s: %d != %d" % (self._lockfile_name, my_pid, pid))