Fatal Python error: GC object already tracked

[urba1n]

Unit-Python with New Relic raises the following errors which prevent the application from running:
Apr 19 08:08:31 unit_as - Fatal Python error: GC object already tracked Apr 19 08:08:32 unit_as - 2018/04/19 08:08:31 [alert] 1#1 process 18 exited on signal 6 (core dumped) Apr 19 08:08:32 unit_as - 2018/04/19 08:08:31 [info] 17#39 *11 shutdown(50, 2) failed (107: Transport endpoint is not connected) Apr 19 08:08:32 unit_as - 2018/04/19 08:08:31 [info] 50#50 "unit-1|18-04-2018|17:33:54" application started Apr 19 08:08:32 unit_as - Fatal Python error: GC object already tracked Apr 19 08:08:32 unit_as - 2018/04/19 08:08:32 [alert] 1#1 process 23 exited on signal 6 (core dumped) Apr 19 08:08:32 unit_as - 2018/04/19 08:08:32 [info] 17#39 *26 shutdown(51, 2) failed (107: Transport endpoint is not connected) Apr 19 08:08:32 unit_as - 2018/04/19 08:08:32 [info] 55#55 "unit-1|18-04-2018|17:33:54" application started Apr 19 08:08:33 unit_as - 2018/04/19 08:08:33 [notice] 50#50 signal signo:17 (SIGCHLD) recevied, ignored

[VBart]

Thank you for the report. Could you please try the following patch in order to check if it fixes the issue?

# HG changeset patch
# User Alexander Borisov <alexander.borisov@nginx.com>
# Date 1524135711 -10800
#      Thu Apr 19 14:01:51 2018 +0300
# Node ID 588c2c58fe7ea06b3130d933e61df4abd8736a6d
# Parent  44f8dcca7f5860a9544a19bbf28c7bf2682cce4a
Python: returning write() callable object from start_respose().

According to PEP (3)333 the start_respose() function must return a write() callable.

diff --git a/src/nxt_python_wsgi.c b/src/nxt_python_wsgi.c
--- a/src/nxt_python_wsgi.c
+++ b/src/nxt_python_wsgi.c
@@ -69,6 +69,7 @@ static PyObject *nxt_python_get_environ(
                       nxt_app_rmsg_t *rmsg, nxt_python_run_ctx_t *ctx);
 
 static PyObject *nxt_py_start_resp(PyObject *self, PyObject *args);
+static PyObject *nxt_py_write(PyObject *self, PyObject *args);
 
 static void nxt_py_input_dealloc(nxt_py_input_t *self);
 static PyObject *nxt_py_input_read(nxt_py_input_t *self, PyObject *args);
@@ -112,6 +113,11 @@ static PyMethodDef nxt_py_start_resp_met
 };
 
 
+static PyMethodDef nxt_py_write_method[] = {
+    {"unit_write", nxt_py_write, METH_O, ""}
+};
+
+
 static PyMethodDef nxt_py_input_methods[] = {
     { "read",      (PyCFunction) nxt_py_input_read,      METH_VARARGS, 0 },
     { "readline",  (PyCFunction) nxt_py_input_readline,  METH_VARARGS, 0 },
@@ -176,6 +182,7 @@ static PyTypeObject nxt_py_input_type = 
 
 static PyObject           *nxt_py_application;
 static PyObject           *nxt_py_start_resp_obj;
+static PyObject           *nxt_py_write_obj;
 static PyObject           *nxt_py_environ_ptyp;
 
 #if PY_MAJOR_VERSION == 3
@@ -263,6 +270,15 @@ nxt_python_init(nxt_task_t *task, nxt_co
 
     nxt_py_start_resp_obj = obj;
 
+    obj = PyCFunction_New(nxt_py_write_method, NULL);
+
+    if (nxt_slow_path(obj == NULL)) {
+        nxt_alert(task, "Python failed to initialize the \"write\" function");
+        goto fail;
+    }
+
+    nxt_py_write_obj = obj;
+
     obj = nxt_python_create_environ(task);
 
     if (obj == NULL) {
@@ -456,6 +472,7 @@ nxt_python_atexit(nxt_task_t *task)
 {
     Py_DECREF(nxt_py_application);
     Py_DECREF(nxt_py_start_resp_obj);
+    Py_DECREF(nxt_py_write_obj);
     Py_DECREF(nxt_py_environ_ptyp);
 
     Py_Finalize();
@@ -845,7 +862,36 @@ nxt_py_start_resp(PyObject *self, PyObje
     /* flush headers */
     nxt_python_write(ctx, cr_lf, sizeof(cr_lf) - 1, 1, 0);
 
-    return args;
+    Py_INCREF(nxt_py_write_obj);
+    return nxt_py_write_obj;
+}
+
+
+static PyObject *
+nxt_py_write(PyObject *self, PyObject *str)
+{
+    nxt_int_t  rc;
+
+    if (nxt_fast_path(!PyBytes_Check(str))) {
+#if PY_MAJOR_VERSION == 3
+        return PyErr_Format(PyExc_TypeError,
+                            "the argument is not a bytestring");
+#else
+        return PyErr_Format(PyExc_TypeError, "the argument is not a string");
+#endif
+    }
+
+    rc = nxt_app_msg_write_raw(nxt_python_run_ctx->task,
+                               nxt_python_run_ctx->wmsg,
+                               (const u_char *) PyBytes_AS_STRING(str),
+                               PyBytes_GET_SIZE(str));
+
+    if (nxt_slow_path(rc != NXT_OK)) {
+        return PyErr_Format(PyExc_RuntimeError,
+                            "failed to write response value");
+    }
+
+    Py_RETURN_NONE;
 }
 

[urba1n]

With this patch the issue is fixed. Thank you very much!

[urba1n]

While the applications is now working with New Relic, I get the following errors in the log at each service call:
Apr 19 16:29:48 unit_as - 2018/04/19 16:29:48 [info] 16#66 *199 shutdown(14, 2) failed (107: Transport endpoint is not connected)
Apr 19 16:29:48 unit_as - 2018/04/19 16:29:48 [info] 16#44 *160 shutdown(14, 2) failed (107: Transport endpoint is not connected)
Apr 19 16:29:48 unit_as - 2018/04/19 16:29:48 [info] 16#64 *202 shutdown(15, 2) failed (107: Transport endpoint is not connected)
Apr 19 16:29:48 unit_as - 2018/04/19 16:29:48 [info] 16#69 *203 shutdown(14, 2) failed (107: Transport endpoint is not connected)
Apr 19 16:29:49 unit_as - 2018/04/19 16:29:49 [info] 16#71 *211 shutdown(15, 2) failed (107: Transport endpoint is not connected)
Apr 19 16:29:49 unit_as - 2018/04/19 16:29:49 [info] 16#68 *206 shutdown(15, 2) failed (107: Transport endpoint is not connected)
Apr 19 16:29:49 unit_as - 2018/04/19 16:29:49 [info] 16#71 *205 shutdown(14, 2) failed (107: Transport endpoint is not connected)