Make pconnect cache keys thread-specific (#1045)

* Make pconnect cache keys thread-specific

Include thread id in the persistent connection cache key so pconnect entries are isolated per thread.
This prevents accidental cross-thread reuse of cached connections.
Add regression test for thread safety of persistent connections.

* Fix PyUnicode_FromFormat reference leaks in pconnect cache key construction

- Ensure PID and thread-id temporary unicode objects are NULL-checked and decref'd after PyUnicode_Concat.
- Prevents incremental memory growth in long-running workloads using persistent connections.

Author: zenflow

ibm_db.c

@@ -1921,6 +1921,8 @@ static PyObject *_python_ibm_db_connect_helper(PyObject *self, PyObject *args, i
     char server[2048];
     int isNewBuffer = 0;
     PyObject *pid = NULL;
+    PyObject *pidStr = NULL;
+    PyObject *threadIdStr = NULL;
     conn_alive = 1;
     if (!PyArg_ParseTuple(args, "OOO|OO", &databaseObj, &uidObj, &passwordObj, &options, &literal_replacementObj))
     {
@@ -1977,9 +1979,24 @@ static PyObject *_python_ibm_db_connect_helper(PyObject *self, PyObject *args, i
             }
             snprintf(messageStr, sizeof(messageStr), "Obtain process id: %p", pid);
             LogMsg(INFO, messageStr);
-            hKey = PyUnicode_Concat(hKey, PyUnicode_FromFormat("%ld", PyLong_AsLong(pid)));
+            pidStr = PyUnicode_FromFormat("%ld", PyLong_AsLong(pid));
+            if (pidStr == NULL)
+            {
+                Py_DECREF(pid);
+                return NULL;
+            }
+            hKey = PyUnicode_Concat(hKey, pidStr);
+            Py_DECREF(pidStr);
             Py_DECREF(pid);
 
+            threadIdStr = PyUnicode_FromFormat("%ld", (long)PyThread_get_thread_ident());
+            if (threadIdStr == NULL)
+            {
+                return NULL;
+            }
+            hKey = PyUnicode_Concat(hKey, threadIdStr);
+            Py_DECREF(threadIdStr);
+
             entry = PyDict_GetItem(persistent_list, hKey);
 
             if (entry != NULL)

ibm_db_tests/test_6793_PconnectThreadIsolation.py

@@ -0,0 +1,90 @@
+#
+#  Licensed Materials - Property of IBM
+#
+#  (c) Copyright IBM Corp. 2007-2008
+#
+
+from __future__ import print_function
+import sys
+import threading
+import unittest
+import ibm_db
+import config
+from testfunctions import IbmDbTestFunctions
+
+
+class IbmDbTestCase(unittest.TestCase):
+
+    def test_6793_PconnectThreadIsolation(self):
+        obj = IbmDbTestFunctions()
+        obj.assert_expect(self.run_test_6793)
+
+    def run_test_6793(self):
+        start_event = threading.Event()
+        lock = threading.Lock()
+        results = []
+        errors = []
+
+        def worker():
+            try:
+                start_event.wait()
+
+                if sys.platform == 'zos':
+                    conn = ibm_db.pconnect(config.database, '', '')
+                else:
+                    conn = ibm_db.pconnect(config.database, config.user, config.password)
+
+                if not conn:
+                    with lock:
+                        errors.append("connect_failed")
+                    return
+
+                is_active = ibm_db.active(conn)
+                conn_id = id(conn)
+                ibm_db.close(conn)
+
+                with lock:
+                    results.append((conn_id, is_active))
+            except Exception:
+                with lock:
+                    errors.append("worker_exception")
+
+        threads = [threading.Thread(target=worker) for _ in range(2)]
+
+        for t in threads:
+            t.start()
+
+        start_event.set()
+
+        for t in threads:
+            t.join()
+
+        if errors:
+            print("errors:", len(errors))
+            return
+
+        unique_conn_handles = len(set([conn_id for conn_id, _ in results]))
+        active_count = sum(1 for _, is_active in results if is_active)
+
+        print("workers:", len(results))
+        print("active_count:", active_count)
+        print("unique_conn_handles:", unique_conn_handles)
+
+
+#__END__
+#__LUW_EXPECTED__
+#workers: 2
+#active_count: 2
+#unique_conn_handles: 2
+#__ZOS_EXPECTED__
+#workers: 2
+#active_count: 2
+#unique_conn_handles: 2
+#__SYSTEMI_EXPECTED__
+#workers: 2
+#active_count: 2
+#unique_conn_handles: 2
+#__IDS_EXPECTED__
+#workers: 2
+#active_count: 2
+#unique_conn_handles: 2