[bug] Fix crash when using custom java object in python async thread

src/main/c/pemja/core/python_class/pyjobject.c

@@ -44,12 +44,19 @@ pyjobject_init(JNIEnv *env, PyJObject *self)
     self->class_name = JcpPyString_FromJString(env, className);
     jcpThread = JcpThread_Get();
 
-    if (jcpThread->name_to_attrs == NULL) {
-        jcpThread->name_to_attrs = PyDict_New();
+    if (jcpThread != NULL) {
+        if (jcpThread->name_to_attrs == NULL) {
+            jcpThread->name_to_attrs = PyDict_New();
+        }
+        cachedAttrs = PyDict_GetItem(jcpThread->name_to_attrs, self->class_name);
+    } else {
+        // On non-pemja threads (e.g., Python async threads), no JcpThread is
+        // available. Clear the error set by JcpThread_Get() and proceed without
+        // the per-thread attribute cache.
+        PyErr_Clear();
+        cachedAttrs = NULL;
     }
 
-    cachedAttrs = PyDict_GetItem(jcpThread->name_to_attrs, self->class_name);
-
     if (cachedAttrs == NULL) {
         cachedAttrs = PyDict_New();
 
@@ -129,8 +136,12 @@ pyjobject_init(JNIEnv *env, PyJObject *self)
         }
         (*env)->DeleteLocalRef(env, fields);
 
-        PyDict_SetItem(jcpThread->name_to_attrs, self->class_name, cachedAttrs);
-        Py_DECREF(cachedAttrs);
+        if (jcpThread != NULL) {
+            PyDict_SetItem(jcpThread->name_to_attrs, self->class_name, cachedAttrs);
+            Py_DECREF(cachedAttrs);
+        }
+        // When jcpThread is NULL, we still own the ref from PyDict_New().
+        // It will be balanced by the Py_DECREF after self->attr assignment below.
     }
 
     if (self->object) {
@@ -140,6 +151,12 @@ pyjobject_init(JNIEnv *env, PyJObject *self)
         self->attr = PyDict_Copy(cachedAttrs);
     }
 
+    // When there is no JcpThread, no cache holds a reference to cachedAttrs,
+    // so we must release the owned ref from PyDict_New() here.
+    if (jcpThread == NULL) {
+        Py_DECREF(cachedAttrs);
+    }
+
     (*env)->PopLocalFrame(env, NULL);
     return 0;
 

src/main/python/pemja/tests/test_async_thread.py

@@ -0,0 +1,103 @@
+################################################################################
+#
+#  Copyright 2022 Alibaba Group Holding Limited.
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+# limitations under the License.
+################################################################################
+
+import asyncio
+import threading
+
+
+# ---------------------------------------------------------------------------
+#  asyncio tests — the event loop runs on a non-pemja thread
+# ---------------------------------------------------------------------------
+
+def test_return_custom_object_in_asyncio(java_obj):
+    """
+    Test that calling a Java method which returns a custom Java object
+    from an asyncio event loop (running on a non-pemja thread) does not
+    crash the JVM.
+
+    Before the fix: SIGSEGV in JcpPyJObject_New (NULL deref on JcpThread).
+    After the fix: works normally.
+    """
+    result = [None]
+    error = [None]
+
+    async def coro():
+        # This runs on the event loop thread (a non-pemja thread).
+        # returnSelf() returns a custom Java object (TestObject), which
+        # goes through JcpPyJObject_New -> pyjobject_init -> JcpThread_Get().
+        obj = java_obj.returnSelf()
+        return str(obj)
+
+    def run_loop():
+        try:
+            loop = asyncio.new_event_loop()
+            asyncio.set_event_loop(loop)
+            result[0] = loop.run_until_complete(coro())
+            loop.close()
+        except Exception as e:
+            error[0] = str(e)
+
+    t = threading.Thread(target=run_loop)
+    t.start()
+    t.join(timeout=10)
+
+    if error[0] is not None:
+        raise RuntimeError("Error in asyncio thread: " + error[0])
+
+    return result[0]
+
+
+def test_return_string_in_asyncio(java_obj):
+    """
+    Control: returning a String (built-in type) from asyncio should always
+    work, even without the fix.
+    """
+    result = [None]
+    error = [None]
+
+    async def coro():
+        return java_obj.returnString()
+
+    def run_loop():
+        try:
+            loop = asyncio.new_event_loop()
+            asyncio.set_event_loop(loop)
+            result[0] = loop.run_until_complete(coro())
+            loop.close()
+        except Exception as e:
+            error[0] = str(e)
+
+    t = threading.Thread(target=run_loop)
+    t.start()
+    t.join(timeout=10)
+
+    if error[0] is not None:
+        raise RuntimeError("Error in asyncio thread: " + error[0])
+
+    return result[0]
+
+
+# ---------------------------------------------------------------------------
+#  Same-thread control test
+# ---------------------------------------------------------------------------
+
+def test_return_custom_object_in_same_thread(java_obj):
+    """
+    Control: calling on the pemja thread itself should always work.
+    """
+    obj = java_obj.returnSelf()
+    return str(obj)

src/test/java/pemja/core/PythonInterpreterTest.java

@@ -361,6 +361,36 @@ public void testCallPythonWithAllTypes() throws Exception {
         }
     }
 
+    @Test
+    public void testCustomObjectInAsyncThread() {
+        PythonInterpreterConfig config =
+                PythonInterpreterConfig.newBuilder().addPythonPaths(testDir).build();
+        try (PythonInterpreter interpreter = new PythonInterpreter(config)) {
+            interpreter.exec("import test_async_thread");
+
+            TestObject obj = new TestObject();
+
+            // Control: returning String from asyncio should always work
+            Object stringResult =
+                    interpreter.invoke("test_async_thread.test_return_string_in_asyncio", obj);
+            assertEquals("hello from java", stringResult);
+
+            // Control: returning custom object on pemja thread should always work
+            Object sameThreadResult =
+                    interpreter.invoke(
+                            "test_async_thread.test_return_custom_object_in_same_thread", obj);
+            assert sameThreadResult != null;
+
+            // This is the bug scenario: returning a custom Java object from
+            // an asyncio event loop (non-pemja thread). Without the fix, this
+            // crashes the JVM with SIGSEGV in JcpPyJObject_New.
+            Object asyncResult =
+                    interpreter.invoke(
+                            "test_async_thread.test_return_custom_object_in_asyncio", obj);
+            assert asyncResult != null;
+        }
+    }
+
     @Test
     public void testCallPyJObject() {
         PythonInterpreterConfig config =
@@ -925,6 +955,16 @@ public String testJavaCallPython(Interpreter interpreter) {
             return interpreter.get("a", String.class);
         }
         /* -------------------------------------------------------------------------------------- */
+
+        /* ----------------------------------- test return custom object ----------------------- */
+        public TestObject returnSelf() {
+            return this;
+        }
+
+        public String returnString() {
+            return "hello from java";
+        }
+        /* -------------------------------------------------------------------------------------- */
     }
 
     private static void deleteDirectory(File directory) throws IOException {