bpo-39984: Move pending calls to PyInterpreterState (GH-19066)

If Py_AddPendingCall() is called in a subinterpreter, the function is
now scheduled to be called from the subinterpreter, rather than being
called from the main interpreter.

Each subinterpreter now has its own list of scheduled calls.

* Move pending and eval_breaker fields from _PyRuntimeState.ceval
  to PyInterpreterState.ceval.
* new_interpreter() now calls _PyEval_InitThreads() to create
  pending calls lock.
* Fix Py_AddPendingCall() for subinterpreters. It now calls
  _PyThreadState_GET() which works in a subinterpreter if the
  caller holds the GIL, and only falls back on
  PyGILState_GetThisThreadState() if _PyThreadState_GET()
  returns NULL.

1 files changed, 7 insertions, 1 deletions

diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index da2bb37af5..b7019e3bb6 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -556,7 +556,7 @@ pycore_create_interpreter(_PyRuntimeState *runtime,
         return status;
     }
 
-    /* Create the GIL */
+    /* Create the GIL and the pending calls lock */
     status = _PyEval_InitThreads(tstate);
     if (_PyStatus_EXCEPTION(status)) {
         return status;
@@ -1581,6 +1581,12 @@ new_interpreter(PyThreadState **tstate_p)
         goto error;
     }
 
+    /* Create the pending calls lock */
+    status = _PyEval_InitThreads(tstate);
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
+
     *tstate_p = tstate;
     return _PyStatus_OK();