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Modernize DECREF (MPI edition). #3207

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merged 3 commits into from
Nov 21, 2024
Merged

Modernize DECREF (MPI edition). #3207

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b43a8c2
Modernize DECREF in `py_alltoall_type` (pdest).
1uc Nov 14, 2024
6c160c3
Decrement reference count early.
1uc Nov 20, 2024
2f40a23
Second attempt of describing the failure.
1uc Nov 20, 2024
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34 changes: 22 additions & 12 deletions src/nrnpython/nrnpy_p2h.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -817,19 +817,19 @@
#if NRNMPI
setpickle();
int root;
PyObject* pdest = NULL;
nb::object pdest;

if (type == 2) {
pdest = py_allgather(psrc.ptr());
pdest = nb::steal(py_allgather(psrc.ptr()));
} else if (type != 1 && type != 5) {
root = size;
if (root < 0 || root >= np) {
hoc_execerror("root rank must be >= 0 and < nhost", 0);
}
if (type == 3) {
pdest = py_gather(psrc.ptr(), root);
pdest = nb::steal(py_gather(psrc.ptr(), root));
} else if (type == 4) {
pdest = py_broadcast(psrc.ptr(), root);
pdest = nb::steal(py_broadcast(psrc.ptr(), root));
}
} else {
if (type == 5) { // scatter
Expand Down Expand Up @@ -883,7 +883,7 @@
sdispl = mk_displ(scnt.data());
rdispl = mk_displ(rcnt);
if (size < 0) {
pdest = nb::make_tuple(sdispl[np], rdispl[np]).release().ptr();
pdest = nb::make_tuple(sdispl[np], rdispl[np]);

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delete[] sdispl;
delete[] rcnt;
delete[] rdispl;
Expand All @@ -892,7 +892,7 @@
nrnmpi_char_alltoallv(s.data(), scnt.data(), sdispl, r, rcnt, rdispl);
delete[] sdispl;

pdest = char2pylist(r, np, rcnt, rdispl);
pdest = nb::steal(char2pylist(r, np, rcnt, rdispl));

delete[] r;
delete[] rcnt;
Expand All @@ -915,19 +915,29 @@
delete[] sdispl;

if (rcnt[0]) {
nb::object po = unpickle(r);
pdest = po.release().ptr();
pdest = unpickle(r);
} else {
pdest = Py_None;
Py_INCREF(pdest);
pdest = nb::none();
}

delete[] rcnt;
assert(rdispl == NULL);
}
}
Object* ho = nrnpy_po2ho(pdest);
Py_XDECREF(pdest);

Object* ho = nrnpy_po2ho(pdest.ptr());

// The problem here is when `pdest` is a HOC object. In that case `ho` has `refcount == 2` but
// must be returned with refcount 0. The `ho` is contained in the `pdest` (which is why the HOC
// refcount is 2) and will be destroyed along with the `pdest` if its reference count is 0.
//
// Therefore, we must first DECREF `pdest` and then decrement `ho->refcount`. If we do
// it the other way around the `Py_DECREF` causes the Python object to be deallocated,
// as part of that deallocation method, the contained HOC object is dereferenced, and because
// it'll have a reference count of 0 it's also be deallocated.
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pdest.dec_ref();
pdest.release();

if (ho) {
--ho->refcount;
}
Expand Down
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