import sqlite3
import shutil
import os
import time
#import threading
import multiprocessing
import subprocess

DBNAME = 'Dummy.db'

#
def test_transaction_lock(pname, copyfile_fn, wait_time=2.0):
    db_conn = sqlite3.connect(DBNAME)
    try:
        db_conn.execute('begin EXCLUSIVE transaction')
        print pname, ": Transaction lock acquired"
        copyfile_fn(DBNAME, DBNAME+'.snapshot')
        time.sleep(wait_time)
    finally:
        db_conn.rollback()
        print name, ": Transaction lock released"
        db_conn.close()

#
# Copy a file with built-in function open (in shutil.copyfile)
#
def shutil_copyfile(*args, **kwargs):
    shutil.copyfile(*args, **kwargs)

#
# Copy a file with os.open
#
def low_copyfile(src, dst):
    ifd = os.open(src, os.O_RDONLY)
    ofd = os.open(dst, os.O_RDWR | os.O_CREAT)
    while 1:
        buf = os.read(ifd, 4096)
        if not buf:
            break
        os.write(ofd, buf)

#
# Copy a file with cp command
#
def command_copyfile(src, dst):
    subprocess.call(['cp', src, dst])


##
## main
##
for copyfile_fn in (shutil_copyfile, low_copyfile, command_copyfile):
    print 'Use %s' % (copyfile_fn,)
    for name in ('process-1', 'process-2'):
        proc = multiprocessing.Process(
            target=test_transaction_lock, args=(name, copyfile_fn))
        proc.start()
        time.sleep(1.0)
    time.sleep(3.0)
    print