1 files changed, 83 insertions, 6 deletions

diff --git a/Modules/_xxsubinterpretersmodule.c b/Modules/_xxsubinterpretersmodule.c
index 2ee8d07d06..e618930e09 100644
--- a/Modules/_xxsubinterpretersmodule.c
+++ b/Modules/_xxsubinterpretersmodule.c
@@ -538,7 +538,7 @@ _channelend_find(_channelend *first, int64_t interp, _channelend **pprev)
 
 typedef struct _channelassociations {
     // Note that the list entries are never removed for interpreter
-    // for which the channel is closed.  This should be a problem in
+    // for which the channel is closed.  This should not be a problem in
     // practice.  Also, a channel isn't automatically closed when an
     // interpreter is destroyed.
     int64_t numsendopen;
@@ -1179,11 +1179,6 @@ _channels_list_all(_channels *channels, int64_t *count)
 {
     int64_t *cids = NULL;
     PyThread_acquire_lock(channels->mutex, WAIT_LOCK);
-    int64_t numopen = channels->numopen;
-    if (numopen >= PY_SSIZE_T_MAX) {
-        PyErr_SetString(PyExc_RuntimeError, "too many channels open");
-        goto done;
-    }
     int64_t *ids = PyMem_NEW(int64_t, (Py_ssize_t)(channels->numopen));
     if (ids == NULL) {
         goto done;
@@ -1392,6 +1387,24 @@ _channel_close(_channels *channels, int64_t id, int end, int force)
     return _channels_close(channels, id, NULL, end, force);
 }
 
+static int
+_channel_is_associated(_channels *channels, int64_t cid, int64_t interp,
+                       int send)
+{
+    _PyChannelState *chan = _channels_lookup(channels, cid, NULL);
+    if (chan == NULL) {
+        return -1;
+    } else if (send && chan->closing != NULL) {
+        PyErr_Format(ChannelClosedError, "channel %" PRId64 " closed", cid);
+        return -1;
+    }
+
+    _channelend *end = _channelend_find(send ? chan->ends->send : chan->ends->recv,
+                                        interp, NULL);
+
+    return (end != NULL && end->open);
+}
+
 /* ChannelID class */
 
 static PyTypeObject ChannelIDtype;
@@ -2324,6 +2337,68 @@ PyDoc_STRVAR(channel_list_all_doc,
 Return the list of all IDs for active channels.");
 
 static PyObject *
+channel_list_interpreters(PyObject *self, PyObject *args, PyObject *kwds)
+{
+    static char *kwlist[] = {"cid", "send", NULL};
+    int64_t cid;            /* Channel ID */
+    int send = 0;           /* Send or receive end? */
+    int64_t id;
+    PyObject *ids, *id_obj;
+    PyInterpreterState *interp;
+
+    if (!PyArg_ParseTupleAndKeywords(
+            args, kwds, "O&$p:channel_list_interpreters",
+            kwlist, channel_id_converter, &cid, &send)) {
+        return NULL;
+    }
+
+    ids = PyList_New(0);
+    if (ids == NULL) {
+        goto except;
+    }
+
+    interp = PyInterpreterState_Head();
+    while (interp != NULL) {
+        id = PyInterpreterState_GetID(interp);
+        assert(id >= 0);
+        int res = _channel_is_associated(&_globals.channels, cid, id, send);
+        if (res < 0) {
+            goto except;
+        }
+        if (res) {
+            id_obj = _PyInterpreterState_GetIDObject(interp);
+            if (id_obj == NULL) {
+                goto except;
+            }
+            res = PyList_Insert(ids, 0, id_obj);
+            Py_DECREF(id_obj);
+            if (res < 0) {
+                goto except;
+            }
+        }
+        interp = PyInterpreterState_Next(interp);
+    }
+
+    goto finally;
+
+except:
+    Py_XDECREF(ids);
+    ids = NULL;
+
+finally:
+    return ids;
+}
+
+PyDoc_STRVAR(channel_list_interpreters_doc,
+"channel_list_interpreters(cid, *, send) -> [id]\n\
+\n\
+Return the list of all interpreter IDs associated with an end of the channel.\n\
+\n\
+The 'send' argument should be a boolean indicating whether to use the send or\n\
+receive end.");
+
+
+static PyObject *
 channel_send(PyObject *self, PyObject *args, PyObject *kwds)
 {
     static char *kwlist[] = {"cid", "obj", NULL};
@@ -2493,6 +2568,8 @@ static PyMethodDef module_functions[] = {
      METH_VARARGS | METH_KEYWORDS, channel_destroy_doc},
     {"channel_list_all",          channel_list_all,
      METH_NOARGS, channel_list_all_doc},
+    {"channel_list_interpreters", (PyCFunction)(void(*)(void))channel_list_interpreters,
+     METH_VARARGS | METH_KEYWORDS, channel_list_interpreters_doc},
     {"channel_send",              (PyCFunction)(void(*)(void))channel_send,
      METH_VARARGS | METH_KEYWORDS, channel_send_doc},
     {"channel_recv",              (PyCFunction)(void(*)(void))channel_recv,