Nogil with jitclass?

wielandbrendel · December 11, 2020, 2:27pm

Dear all,
I am trying to use joblib parallel (with threading backend) to parallelize a set of calls to a jitclass. That doesn’t seem to work, probably because jitclass doesn’t release the GIL. Is there a way to pass something like nogil=True to jitclass, or is that generally not supported?

Thanks!

stuartarchibald · December 11, 2020, 5:21pm

Hi @wielandbrendel,

From memory, @njit flags in general cannot be passed to jitclass, construction is “automatic” and uses njit directly.

github.com

numba/numba/blob/release0.52/numba/experimental/jitclass/base.py#L110


    init = cls.class_type.instance_type.methods['__init__']
    init_sig = utils.pysignature(init)
    # get postitional and keyword arguments
    # offset by one to exclude the `self` arg
    args = _getargs(init_sig)[1:]
    cls._ctor_sig = init_sig
    ctor_source = _ctor_template.format(args=', '.join(args))
    glbls = {"__numba_cls_": cls}
    exec(ctor_source, glbls)
    ctor = glbls['ctor']
    cls._ctor = njit(ctor)
def __instancecheck__(cls, instance):
    if isinstance(instance, _box.Box):
        return instance._numba_type_.class_type is cls.class_type
    return False
def __call__(cls, *args, **kwargs):
    # The first argument of _ctor_sig is `cls`, which here
    # is bound to None and then skipped when invoking the constructor.
    bind = cls._ctor_sig.bind(None, *args, **kwargs)

github.com

numba/numba/blob/release0.52/numba/experimental/jitclass/base.py#L217-L229


jit_methods = {k: njit(v) for k, v in methods.items()}
jit_props = {}
for k, v in props.items():
    dct = {}
    if v.fget:
        dct['get'] = njit(v.fget)
    if v.fset:
        dct['set'] = njit(v.fset)
    jit_props[k] = dct
jit_static_methods = {
    k: njit(v.__func__) for k, v in static_methods.items()}

Hope that answers your question?

wielandbrendel · December 12, 2020, 8:52am

Thanks so much! So the short answer is: it is currently not possible to use jitclass without GIL, right?

stuartarchibald · December 14, 2020, 10:57am

Yes, this is the case.

nelson2005 · January 5, 2021, 12:08pm

I’m sure I’m misunderstanding, but I had thought that a nogil njit function calling another not-declared-nogil njit function would not reacquire the gil- is that correct? Sample pseudocode:

@njit(nogil=False)
def has_gil():
    # is gil owned here?
    pass

@njit(nogil=True)
def no_gil():
    has_gil()

no_gil()