diff --git a/uvloop/cbhandles.pyx b/uvloop/cbhandles.pyx
index 2914b42e..ad18fe94 100644
--- a/uvloop/cbhandles.pyx
+++ b/uvloop/cbhandles.pyx
@@ -1,3 +1,20 @@
+cdef inline void _debug_cb_handles_inc(Loop loop):
+    if _debug_cb_handles_lock != NULL:
+        PyThread_acquire_lock(_debug_cb_handles_lock, 1)
+    loop._debug_cb_handles_total += 1
+    loop._debug_cb_handles_count += 1
+    if _debug_cb_handles_lock != NULL:
+        PyThread_release_lock(_debug_cb_handles_lock)
+
+
+cdef inline void _debug_cb_handles_dec(Loop loop):
+    if _debug_cb_handles_lock != NULL:
+        PyThread_acquire_lock(_debug_cb_handles_lock, 1)
+    loop._debug_cb_handles_count -= 1
+    if _debug_cb_handles_lock != NULL:
+        PyThread_release_lock(_debug_cb_handles_lock)
+
+
 @cython.no_gc_clear
 @cython.freelist(DEFAULT_FREELIST_SIZE)
 cdef class Handle:
@@ -9,8 +26,7 @@ cdef class Handle:
     cdef inline _set_loop(self, Loop loop):
         self.loop = loop
         if UVLOOP_DEBUG:
-            loop._debug_cb_handles_total += 1
-            loop._debug_cb_handles_count += 1
+            _debug_cb_handles_inc(loop)
         if loop._debug:
             self._source_traceback = extract_stack()
 
@@ -21,7 +37,7 @@ cdef class Handle:
 
     def __dealloc__(self):
         if UVLOOP_DEBUG and self.loop is not None:
-            self.loop._debug_cb_handles_count -= 1
+            _debug_cb_handles_dec(self.loop)
         if self.loop is None:
             raise RuntimeError('Handle.loop is None in Handle.__dealloc__')
 
@@ -423,10 +439,14 @@ cdef extract_stack():
     if f is None:
         return
 
+    if getattr(f, "f_lineno", None) is None or getattr(f, "f_code", None) is None:
+        return None
     try:
         stack = tb_StackSummary.extract(tb_walk_stack(f),
                                         limit=DEBUG_STACK_DEPTH,
                                         lookup_lines=False)
+    except (AttributeError, TypeError):
+        return None
     finally:
         f = None
 
diff --git a/uvloop/loop.pyx b/uvloop/loop.pyx
index 2ed1f272..4eb1495c 100644
--- a/uvloop/loop.pyx
+++ b/uvloop/loop.pyx
@@ -31,6 +31,12 @@ from libc cimport errno
 from cpython cimport PyObject
 from cpython cimport PyErr_CheckSignals, PyErr_Occurred
 from cpython cimport PyThread_get_thread_ident
+from cpython.pythread cimport (
+    PyThread_type_lock,
+    PyThread_allocate_lock,
+    PyThread_acquire_lock,
+    PyThread_release_lock,
+)
 from cpython cimport Py_INCREF, Py_DECREF, Py_XDECREF, Py_XINCREF
 from cpython cimport (
     PyObject_GetBuffer, PyBuffer_Release, PyBUF_SIMPLE,
@@ -52,6 +58,7 @@ cdef:
     int PY311 = PY_VERSION_HEX >= 0x030b0000
     int PY313 = PY_VERSION_HEX >= 0x030d0000
     uint64_t MAX_SLEEP = 3600 * 24 * 365 * 100
+    PyThread_type_lock _debug_cb_handles_lock = PyThread_allocate_lock()
 
 
 cdef _is_sock_stream(sock_type):