python
diff --git a/‎Include/cpython/pystate.h
Lines changed: 1 addition & 5 deletions b/‎Include/cpython/pystate.h
Lines changed: 1 addition & 5 deletions
diff --git a/‎Include/internal/pycore_pystate.h
Lines changed: 12 additions & 0 deletions b/‎Include/internal/pycore_pystate.h
Lines changed: 12 additions & 0 deletions
diff --git a/‎Python/pystate.c
Lines changed: 12 additions & 5 deletions b/‎Python/pystate.c
Lines changed: 12 additions & 5 deletions
@@ -114,11 +114,7 @@ struct _ts {
     PyThreadState *next;
     PyInterpreterState *interp;
 
-    /* Has been initialized to a safe state.
-
-       In order to be effective, this must be set to 0 during or right
-       after allocation. */
-    int _initialized;
+    int _status;
 
     int py_recursion_remaining;
     int py_recursion_limit;
 
@@ -139,6 +139,18 @@ _PyThreadState_UpdateTracingState(PyThreadState *tstate)
 }
 
 
+/* PyThreadState status */
+
+#define PyThreadState_UNINITIALIZED 0
+/* Has been initialized to a safe state.
+
+   In order to be effective, this must be set to 0 during or right
+   after allocation. */
+#define PyThreadState_INITIALIZED 1
+#define PyThreadState_BOUND 2
+#define PyThreadState_UNBOUND 3
+
+
 /* Other */
 
 PyAPI_FUNC(PyThreadState *) _PyThreadState_Swap(
 
@@ -152,6 +152,7 @@ static void
 bind_tstate(PyThreadState *tstate)
 {
     assert(tstate != NULL);
+    assert(tstate->_status == PyThreadState_INITIALIZED);
     assert(tstate->thread_id == 0);
     assert(tstate->native_thread_id == 0);
     _PyRuntimeState *runtime = tstate->interp->runtime;
@@ -183,12 +184,15 @@ bind_tstate(PyThreadState *tstate)
 #ifdef PY_HAVE_THREAD_NATIVE_ID
     tstate->native_thread_id = PyThread_get_thread_native_id();
 #endif
+
+    tstate->_status = PyThreadState_BOUND;
 }
 
 static void
 unbind_tstate(PyThreadState *tstate)
 {
     assert(tstate != NULL);
+    assert(tstate->_status == PyThreadState_BOUND);
     assert(tstate->thread_id > 0);
 #ifdef PY_HAVE_THREAD_NATIVE_ID
     assert(tstate->native_thread_id > 0);
@@ -201,9 +205,12 @@ unbind_tstate(PyThreadState *tstate)
         current_tss_clear(runtime);
     }
 
-    // -1 makes sure the thread state won't be re-bound.
-    tstate->thread_id = -1;
-    tstate->native_thread_id = -1;
+    // We leave thread_id and native_thraed_id alone
+    // since they can be useful for debugging.
+    // Check the `_status` field to know if these values
+    // are still valid.
+
+    tstate->_status = PyThreadState_UNBOUND;
 }
 
 /* This is not exported, as it is not reliable!  It can only
@@ -984,7 +991,7 @@ init_threadstate(PyThreadState *tstate,
                  PyInterpreterState *interp, uint64_t id,
                  PyThreadState *next)
 {
-    if (tstate->_initialized) {
+    if (tstate->_status != PyThreadState_UNINITIALIZED) {
         Py_FatalError("thread state already initialized");
     }
 
@@ -1020,7 +1027,7 @@ init_threadstate(PyThreadState *tstate,
     tstate->datastack_top = NULL;
     tstate->datastack_limit = NULL;
 
-    tstate->_initialized = 1;
+    tstate->_status = PyThreadState_INITIALIZED;
 }
 
 static PyThreadState *