[Python-Dev] pre-PEP: The Safe Buffer Interface

[Thomas Heller]

[Scott]
> > A single lock interface can be implemented over an object without any
> > locking.  Have the lockable object return simple "fixed buffer objects"
> > with a limited lifespan.
> 
[Neil]
>    This returns to the possibility of indeterminate lifespan as mentioned
> earlier in the thread.
> 

Can't you do something like this (maybe this is what Scott has in mind):

static void _unlock(void *ptr, MyObject *self)
{
    /* do whatever needed to unlock the object */
    self->locked--;
    Py_DECREF(self);
}

static PyObject*
MyObject_GetBuffer(MyObject *self)
{
    /* Do whatever needed to lock the object */
    self->lock++;
    Py_INCREF(self);
    return PyCObject_FromVoidPtrAndDesc(self->ptr,
                                        self,
                                        _unlock)
}

In plain text:
Provide a method which returns a 'view' into your object's
buffer after locking the object. The view holds a reference
to object, the objects is unlocked and decref'd when the
view is destroyed.
In practice something better than a PyCObject will be used,
and this one can even implement the 'fixed buffer' interface.

Thomas