mimic flock with sqlite

lock_with_sqlite.py

import sqlite3
import time
import random;
import sys;
locker_dbpath = "dummy_locker.db";
locker_tablename = "dummy_table";
locker_conn = None;

#public domain


def get_lock():
    global locker_conn;
    global locker_tablename;
    global locker_dbpath;
    
    try:
        locker_conn = sqlite3.connect(locker_dbpath, isolation_level='EXCLUSIVE')
        locker_conn.execute("DROP TABLE IF EXISTS "+locker_tablename)
        locker_conn.execute("create table "+locker_tablename+" (tid int)")
        locker_conn.execute("insert into "+locker_tablename+" values(1)")
    except sqlite3.OperationalError :
        if not locker_conn == None:
            locker_conn.close();
        return False;
    return True;
    
def release_lock():
    global locker_conn;
    if not locker_conn == None:
        locker_conn.commit();
        locker_conn.close();
#---------- example code --------------
#call this script multiple times.
import os;
processid = str(os.getpid());
for ii in range(100):
    lchk = get_lock();
    if lchk:
        sys.stdout.write(" processing "+processid+" >>>");
        sys.stdout.flush();
        time.sleep(int(20*random.random()+1));
        sys.stdout.write(" finished "+processid+".\n");
        release_lock();
        time.sleep(5*random.random());
    else:
        sys.stdout.write("\ntried "+processid+" but db was locked.\n");
    time.sleep(5*random.random());