bpo-29102: Add a unique ID to PyInterpreterState. (#1639)

1 files changed, 37 insertions, 0 deletions

diff --git a/Python/pystate.c b/Python/pystate.c
index 52899f1..99a579a 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -65,6 +65,23 @@ PyThreadFrameGetter _PyThreadState_GetFrame = NULL;
 static void _PyGILState_NoteThreadState(PyThreadState* tstate);
 #endif
 
+/* _next_interp_id is an auto-numbered sequence of small integers.
+   It gets initialized in _PyInterpreterState_Init(), which is called
+   in Py_Initialize(), and used in PyInterpreterState_New().  A negative
+   interpreter ID indicates an error occurred.  The main interpreter
+   will always have an ID of 0.  Overflow results in a RuntimeError.
+   If that becomes a problem later then we can adjust, e.g. by using
+   a Python int.
+
+   We initialize this to -1 so that the pre-Py_Initialize() value
+   results in an error. */
+static int64_t _next_interp_id = -1;
+
+void
+_PyInterpreterState_Init(void)
+{
+    _next_interp_id = 0;
+}
 
 PyInterpreterState *
 PyInterpreterState_New(void)
@@ -103,6 +120,15 @@ PyInterpreterState_New(void)
         HEAD_LOCK();
         interp->next = interp_head;
         interp_head = interp;
+        if (_next_interp_id < 0) {
+            /* overflow or Py_Initialize() not called! */
+            PyErr_SetString(PyExc_RuntimeError,
+                            "failed to get an interpreter ID");
+            interp = NULL;
+        } else {
+            interp->id = _next_interp_id;
+            _next_interp_id += 1;
+        }
         HEAD_UNLOCK();
     }
 
@@ -170,6 +196,17 @@ PyInterpreterState_Delete(PyInterpreterState *interp)
 }
 
 
+int64_t
+PyInterpreterState_GetID(PyInterpreterState *interp)
+{
+    if (interp == NULL) {
+        PyErr_SetString(PyExc_RuntimeError, "no interpreter provided");
+        return -1;
+    }
+    return interp->id;
+}
+
+
 /* Default implementation for _PyThreadState_GetFrame */
 static struct _frame *
 threadstate_getframe(PyThreadState *self)