#!/usr/bin/env python3

'''Multiprocessing test.

PgManager is partially safe against process forking.

You can create connection credentials (create_conn) in main process, then fork

and continue working with pgmanager in children processes. You can call create_conn again

in children, but new connection credentials will be accessible only from process

where it was created -- no sharing between processes.

get_conn and cursor will still work after fork. Connections from parent process will

be forgotten, that cannot be used un child process. 

Connections cannot be shared between processes, DO NOT:

 * get_conn, then fork, then put_conn

 * get_conn, then fork, then use the connection, then .close()

Good usage:

 * create_conn, fork, get_conn, cursor, etc.

Basically, you can transfer only information from create_conn(), nothing else.

'''

import multiprocessing

from config import Config

from pgtoolkit import pgmanager

def sub1(id):

    with pgm.cursor() as curs:

        print('[%d] pgconn: %d' % (multiprocessing.current_process().pid, curs.connection.get_backend_pid()))

        print('[%d] update' % multiprocessing.current_process().pid)

        curs.execute('''UPDATE test SET name = 'multi-1' WHERE id=%s''', [id])

        print('[%d] commit' % multiprocessing.current_process().pid)

        curs.connection.commit()

def sub2(id):

    pgm = pgmanager.get_instance()

    with pgm.cursor() as curs:

        print('[%d] pgconn: %d' % (multiprocessing.current_process().pid, curs.connection.get_backend_pid()))

        print('[%d] update' % multiprocessing.current_process().pid)

        curs.execute('''UPDATE test SET name = 'multi-2' WHERE id=%s''', [id])

        print('[%d] commit' % multiprocessing.current_process().pid)

        curs.connection.commit()

cfg = Config('tests.conf')

pgm = pgmanager.get_instance()

pgm.create_conn(**cfg)

with pgm.cursor() as curs:

    print('[%d] pgconn: %d' % (multiprocessing.current_process().pid, curs.connection.get_backend_pid()))    

    print('[%d] insert' % multiprocessing.current_process().pid)

    curs.execute('''INSERT INTO test (name) VALUES ('multi') RETURNING id''')

    id = curs.fetchone()[0]

    curs.connection.commit()

    print('[%d] update' % multiprocessing.current_process().pid)

    curs.execute('''UPDATE test SET name = 'multi-main' WHERE id=%s''', [id])

    # not committed

p1 = multiprocessing.Process(target=sub1, args=[id])

p1.start()

p2 = multiprocessing.Process(target=sub2, args=[id])

p2.start()

with pgm.cursor() as curs:

    print('[%d] commit' % multiprocessing.current_process().pid)

    curs.connection.commit()

print('join')

p1.join()

p2.join()

print('done')