My environment

• Python 2.7.3
• Ubuntu 14.04
• Source code I'm using: CPython on GitHub

Additional information to understand my question

As far as my understanding is concerned, Modules/_multiprocessing/semaphore.c

implements the internal Python SemLock object that is used to implement multiprocessing.synchronize.SemLock

in the Python standard library:

class SemLock(object):
    def __init__(self, kind, value, maxvalue, *, ctx):
        (...A lot of other code...)
                sl = self._semlock = _multiprocessing.SemLock(  # <-- Here.

      

        
        
        
      

    

Modules/_multiprocessing/semaphore.c

implements this internal SemLock object by defining a SemLockObject in C and exporting it as a SemLock in Python.

Here is the definition of C:

typedef struct {
    PyObject_HEAD
    SEM_HANDLE handle;
    unsigned long last_tid;
    int count;
    int maxvalue;
    int kind;
    char *name;  /* <--- It has 'name'. */
} SemLockObject;

      

        
        
        
      

    

Later SemLockObject is exported as SemLock, in Line # 617 :

PyTypeObject _PyMp_SemLockType = {
    PyVarObject_HEAD_INIT(NULL, 0)
    /* tp_name           */ "_multiprocessing.SemLock",
    /* tp_basicsize      */ sizeof(SemLockObject),

      

        
        
        
      

    

Several _semlock_members_ are also exported with SemLock, including "name". See Line # 608 :

static PyMemberDef semlock_members[] = {
    {"handle", T_SEM_HANDLE, offsetof(SemLockObject, handle), READONLY,
     ""},
    {"kind", T_INT, offsetof(SemLockObject, kind), READONLY,
     ""},
    {"maxvalue", T_INT, offsetof(SemLockObject, maxvalue), READONLY,
     ""},
    {"name", T_STRING, offsetof(SemLockObject, name), READONLY,
     ""},  /* <--- Here it is. */
    {NULL}
};

      

        
        
        
      

    

Therefore, there is reason to believe that at runtime I can access the name element . However, when I check the members of this internal SemLock object, I do not see the name member . Here is my verification code:

import multiprocessing as mp
import inspect

lock = mp.Semaphore(1)
members = inspect.getmembers(lock._semlock)
for (name, _) in members:
    print name

      

        
        
        
      

    

Here's the result:

SEM_VALUE_MAX
__class__
__delattr__
__doc__
__enter__
__exit__
__format__
__getattribute__
__hash__
__init__
__new__
__reduce__
__reduce_ex__
__repr__
__setattr__
__sizeof__
__str__
__subclasshook__
_after_fork
_count
_get_value
_is_mine
_is_zero
_rebuild 
acquire 
handle      <-- 'handle' is defined in 'semlock_members'
kind        <-- 'kind' is defined in 'semlock_members'
maxvalue    <-- 'maxvalue' is defined in 'semlock_members'
release

      

        
        
        
      

    

But where is the name ??

In fact, if we look at multiprocessing.synchronize.SemLock.__init__

Line # 76 , it checks the value _semlock.name

:

if self._semlock.name is not None:

      

        
        
        
      

    

which makes me think the base _semlock has a 'name' member because otherwise the code would throw an exception such as an AttributeError object: '_multiprocessing.SemLock' has no 'name' attribute. "

I must have missed something. Can anyone help me point this out?