python callbacks not making new thread on every cb invocation

conc.c

/* cc -shared conc.c -o conc.dynlib */
#include <pthread.h>
#include <stdio.h>

typedef void (*cb_t)(int);

pthread_t t;
cb_t cb;

void set_notify(cb_t cb0) {
    cb = cb0;
}

void* run() {
    printf("C thread - in thread begin\n");
    int i;
    for (i = 0; i < 3; i++) {
        printf("C thread - in thread; notify begin: %d\n", i);
        cb(i);
        printf("C thread - in thread; notify end: %d\n", i);
    }
    printf("C thread - in thread; done\n");
    
    return NULL;
}

void start() {
    printf("C thread - starting thread\n");
    pthread_create(&t, NULL, *run, NULL);
    pthread_join(t, NULL);
    printf("C thread - joined thread\n");
}

conc.py

#! /usr/bin/env python

import threading
import ctypes
import os

print os.getpid()

ev = threading.Event()

def t_id():
    t = threading.current_thread()
    id = "%d-%s" % (t.ident, t.name)
    return id 

def notifier(n):
    print 'PYTHON - notify begin', t_id(), n
    ev.set()
    print 'PYTHON - notify done', t_id(), n

def consumer():
    print 'PYTHON - consume waiting', t_id()
    ev.wait()
    print 'PYTHON - consume done', t_id()
    ev.clear()

lib = ctypes.CDLL('./conc.dynlib')
print('Loaded lib {0}'.format(lib))

cb_t = ctypes.CFUNCTYPE(None, ctypes.c_int)

lib.set_notify.argtypes=[cb_t]
lib.set_notify.restype=None

lib.start.argtypes=[]
lib.start.restype=None 

cb = cb_t(notifier)
lib.set_notify(cb)

t2 = threading.Thread(group=None, target=consumer)
t2.start()

lib.start()

t2.join()

print 'done'

output

65464
Loaded lib <CDLL './conc.dynlib', handle 7fdc436116f0 at 10ad76190>
PYTHON - consume waiting 123145306509312-Thread-1
C thread - starting thread
C thread - in thread begin
C thread - in thread; notify begin: 0
PYTHON - notify begin 123145307045888-Dummy-2 0
PYTHON - notify done 123145307045888-Dummy-2 0
C thread - in thread; notify end: 0
C thread - in thread; notify begin: 1
PYTHON - notify begin 123145307045888-Dummy-2 1
PYTHON - notify done 123145307045888-Dummy-2 1
C thread - in thread; notify end: 1
C thread - in thread; notify begin: 2
PYTHON - consume done 123145306509312-Thread-1
 PYTHON - notify begin 123145307045888-Dummy-2 2
PYTHON - notify done 123145307045888-Dummy-2 2
C thread - in thread; notify end: 2
C thread - in thread; done
C thread - joined thread
done