1 #!/usr/bin/env python3

     2 '''Multiprocessing test.

     3 

     4 PgManager is partially safe against process forking.

     5 

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

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

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

     9 where it was created -- no sharing between processes.

    10 

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

    12 be forgotten, that cannot be used un child process. 

    13 

    14 Connections cannot be shared between processes, DO NOT:

    15  * get_conn, then fork, then put_conn

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

    17 

    18 Good usage:

    19  * create_conn, fork, get_conn, cursor, etc.

    20 

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

    22 

    23 '''

    24 

    25 

    26 import multiprocessing

    27 

    28 from config import Config

    29 from pgtoolkit import pgmanager

    30 

    31 

    32 def sub1(id):

    33     with pgm.cursor() as curs:

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

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

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

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

    38         curs.connection.commit()

    39 

    40 def sub2(id):

    41     pgm = pgmanager.get_instance()

    42     with pgm.cursor() as curs:

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

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

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

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

    47         curs.connection.commit()

    48 

    49 

    50 cfg = Config('tests.conf')

    51 pgm = pgmanager.get_instance()

    52 pgm.create_conn(**cfg)

    53 

    54 with pgm.cursor() as curs:

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

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

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

    58     id = curs.fetchone()[0]

    59     curs.connection.commit()

    60     

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

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

    63     # not committed

    64 

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

    66 p1.start()

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

    68 p2.start()

    69 

    70 with pgm.cursor() as curs:

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

    72     curs.connection.commit()

    73 

    74 print('join')

    75 p1.join()

    76 p2.join()

    77 

    78 print('done')