2 files changed, 29 insertions, 6 deletions

diff --git a/Python/ceval_gil.c b/Python/ceval_gil.c
index ad33a58..a390bec 100644
--- a/Python/ceval_gil.c
+++ b/Python/ceval_gil.c
@@ -500,9 +500,18 @@ PyEval_ThreadsInitialized(void)
 }
 
 PyStatus
-_PyEval_InitGIL(PyThreadState *tstate)
+_PyEval_InitGIL(PyThreadState *tstate, int own_gil)
 {
     assert(tstate->interp->ceval.gil == NULL);
+    if (!own_gil) {
+        PyInterpreterState *main_interp = _PyInterpreterState_Main();
+        assert(tstate->interp != main_interp);
+        struct _gil_runtime_state *gil = main_interp->ceval.gil;
+        assert(gil_created(gil));
+        tstate->interp->ceval.gil = gil;
+        tstate->interp->ceval.own_gil = 0;
+        return _PyStatus_OK();
+    }
 
     /* XXX per-interpreter GIL */
     struct _gil_runtime_state *gil = &tstate->interp->runtime->ceval.gil;
@@ -512,8 +521,11 @@ _PyEval_InitGIL(PyThreadState *tstate)
            and destroy it. */
         assert(gil_created(gil));
         tstate->interp->ceval.gil = gil;
+        // XXX For now we lie.
+        tstate->interp->ceval.own_gil = 1;
         return _PyStatus_OK();
     }
+    assert(own_gil);
 
     assert(!gil_created(gil));
 
@@ -521,6 +533,7 @@ _PyEval_InitGIL(PyThreadState *tstate)
     create_gil(gil);
     assert(gil_created(gil));
     tstate->interp->ceval.gil = gil;
+    tstate->interp->ceval.own_gil = 1;
     take_gil(tstate);
     return _PyStatus_OK();
 }
@@ -530,6 +543,14 @@ _PyEval_FiniGIL(PyInterpreterState *interp)
 {
     if (interp->ceval.gil == NULL) {
         /* It was already finalized (or hasn't been initialized yet). */
+        assert(!interp->ceval.own_gil);
+        return;
+    }
+    else if (!interp->ceval.own_gil) {
+        PyInterpreterState *main_interp = _PyInterpreterState_Main();
+        assert(interp != main_interp);
+        assert(interp->ceval.gil == main_interp->ceval.gil);
+        interp->ceval.gil = NULL;
         return;
     }
 
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 97957d3..7057086 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -585,7 +585,7 @@ init_interp_settings(PyInterpreterState *interp,
 
 
 static PyStatus
-init_interp_create_gil(PyThreadState *tstate)
+init_interp_create_gil(PyThreadState *tstate, int own_gil)
 {
     PyStatus status;
 
@@ -600,7 +600,7 @@ init_interp_create_gil(PyThreadState *tstate)
     }
 
     /* Create the GIL and take it */
-    status = _PyEval_InitGIL(tstate);
+    status = _PyEval_InitGIL(tstate, own_gil);
     if (_PyStatus_EXCEPTION(status)) {
         return status;
     }
@@ -632,7 +632,9 @@ pycore_create_interpreter(_PyRuntimeState *runtime,
         return status;
     }
 
-    const PyInterpreterConfig config = _PyInterpreterConfig_LEGACY_INIT;
+    PyInterpreterConfig config = _PyInterpreterConfig_LEGACY_INIT;
+    // The main interpreter always has its own GIL.
+    config.own_gil = 1;
     status = init_interp_settings(interp, &config);
     if (_PyStatus_EXCEPTION(status)) {
         return status;
@@ -645,7 +647,7 @@ pycore_create_interpreter(_PyRuntimeState *runtime,
     _PyThreadState_Bind(tstate);
     (void) PyThreadState_Swap(tstate);
 
-    status = init_interp_create_gil(tstate);
+    status = init_interp_create_gil(tstate, config.own_gil);
     if (_PyStatus_EXCEPTION(status)) {
         return status;
     }
@@ -2047,7 +2049,7 @@ new_interpreter(PyThreadState **tstate_p, const PyInterpreterConfig *config)
         goto error;
     }
 
-    status = init_interp_create_gil(tstate);
+    status = init_interp_create_gil(tstate, config->own_gil);
     if (_PyStatus_EXCEPTION(status)) {
         goto error;
     }