fix(imperative): fix dangling pointer in dispatcher

GitOrigin-RevId: b21f7e06f01e780486b2cf1e9495662b02934546

imperative/python/src/dispatcher.cpp

@@ -11,6 +11,7 @@
 
 #include "./dispatcher.h"
 #include "./pyext17.h"
+#include "megbrain/exception.h"
 #include "megbrain/utils/hash.h"
 #include "megbrain/utils/small_vector.h"
 
@@ -56,9 +57,25 @@ struct ObjectIdHash : std::hash<void*> {
     }
 };
 
+namespace {
+using Container = std::vector<Frame>;
+struct DispatcherStack: Container {
+    constexpr static size_t MAX_RECURSIVE_DEPTH = 1024u;
+    DispatcherStack() { reserve(MAX_RECURSIVE_DEPTH); }
+
+    template<typename... Args>
+    auto&& emplace_back_safely(Args&& ...args) {
+        mgb_throw_if(size() >= MAX_RECURSIVE_DEPTH, mgb::MegBrainError,
+            "recursion depth %zu is greater than the MAX_RECURSIVE_DEPTH(%zu)",
+            size(), MAX_RECURSIVE_DEPTH);
+        return emplace_back(std::forward<Args>(args)...);
+    }
+};
+} // anonymous namespace
+
 struct Dispatcher {
     std::unordered_map<FastSig, std::unique_ptr<MRO>, FastSigHash> cache;
-    std::vector<Frame> stack;
+    DispatcherStack stack;
     std::unordered_map<py::object, std::unique_ptr<Handler>, ObjectIdHash> registry;
 
     inline py::handle self() {
@@ -78,7 +95,7 @@ struct Dispatcher {
                 return false;
             }
         }
-        stack.emplace_back(it->second.get());
+        stack.emplace_back_safely(it->second.get());
         return true;
     }
 
@@ -145,7 +162,7 @@ public:
             PyErr_SetString(PyExc_RuntimeError, "super called at top level");
             return nullptr;
         }
-        stack.emplace_back(stack.back()).mro_offset++;
+        stack.emplace_back_safely(stack.back()).mro_offset++;
         return do_call([=](PyObject* func){return _PyObject_FastCall(func, const_cast<PyObject**>(args), nargs);});
     }