[mlir][python] fix PyDenseResourceElementsAttribute finalizer (#150561)

This PR melds https://github.com/llvm/llvm-project/pull/150137 and
https://github.com/llvm/llvm-project/pull/149414 *and* partially reverts
https://github.com/llvm/llvm-project/pull/124832.

The summary is the `PyDenseResourceElementsAttribute` finalizer/deleter
has/had two problems

1. wasn't threadsafe (can be called from a different thread than that
which currently holds the GIL)
2. can be called while the interpreter is "not initialized"

https://github.com/llvm/llvm-project/pull/124832 for some reason decides
to re-initialize the interpreter to avoid case 2 and runs afoul of the
fact that `Py_IsInitialized` can be false during the finalization of the
interpreter itself (e.g., at the end of a script).

I don't know why this decision was made (I missed the PR) but I believe
we should never be calling
[Py_Initialize](https://docs.python.org/3/c-api/init.html#c.Py_Initialize):

> In an application \*\*\*\***embedding Python**\*\*\*\*, this should be
called before using any other Python/C API functions

**but we aren't embedding Python**!

So therefore we will only be in case 2 when the interpreter is being
finalized and in that case we should just leak the buffer.

Note,
[lldb](https://github.com/llvm/llvm-project/blob/548ca9e97673a168023a616d311d901ca04b29a3/lldb/source/Plugins/ScriptInterpreter/Python/PythonDataObjects.cpp#L81-L93)
does a similar sort of thing for its finalizers.

Co-authored-by: Anton Korobeynikov <anton@korobeynikov.info>
Co-authored-by: Max Manainen <maximmanainen@gmail.com>

Co-authored-by: Anton Korobeynikov <anton@korobeynikov.info>
Co-authored-by: Max Manainen <maximmanainen@gmail.com>

1 files changed, 10 insertions, 3 deletions

diff --git a/mlir/lib/Bindings/Python/IRAttributes.cpp b/mlir/lib/Bindings/Python/IRAttributes.cpp
index 8f79caf..db84ee1 100644
--- a/mlir/lib/Bindings/Python/IRAttributes.cpp
+++ b/mlir/lib/Bindings/Python/IRAttributes.cpp
@@ -16,8 +16,8 @@
 #include "NanobindUtils.h"
 #include "mlir-c/BuiltinAttributes.h"
 #include "mlir-c/BuiltinTypes.h"
-#include "mlir/Bindings/Python/NanobindAdaptors.h"
 #include "mlir/Bindings/Python/Nanobind.h"
+#include "mlir/Bindings/Python/NanobindAdaptors.h"
 #include "llvm/ADT/ScopeExit.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -1428,6 +1428,12 @@ public:
   }
 };
 
+// Check if the python version is less than 3.13. Py_IsFinalizing is a part
+// of stable ABI since 3.13 and before it was available as _Py_IsFinalizing.
+#if PY_VERSION_HEX < 0x030d0000
+#define Py_IsFinalizing _Py_IsFinalizing
+#endif
+
 class PyDenseResourceElementsAttribute
     : public PyConcreteAttribute<PyDenseResourceElementsAttribute> {
 public:
@@ -1474,8 +1480,9 @@ public:
     // The userData is a Py_buffer* that the deleter owns.
     auto deleter = [](void *userData, const void *data, size_t size,
                       size_t align) {
-      if (!Py_IsInitialized())
-        Py_Initialize();
+      if (Py_IsFinalizing())
+        return;
+      assert(Py_IsInitialized() && "expected interpreter to be initialized");
       Py_buffer *ownedView = static_cast<Py_buffer *>(userData);
       nb::gil_scoped_acquire gil;
       PyBuffer_Release(ownedView);