Bugfix: PyTuple_SetItem() "steals" a reference.

[libsigrokdecode.git] / decode.c

diff --git a/decode.c b/decode.c
index 6acbd10455f48da6dfb00516e4c94a3f3eb6ebb8..c2beab29a6bc619fbb783aae3d2d14db2d3f8858 100644 (file)
--- a/decode.c
+++ b/decode.c
@@ -34,6 +34,19 @@
 /* The list of protocol decoders. */
 GSList *list_pds = NULL;
 
+/*
+ * Here's a quick overview of Python/C API reference counting.
+ *
+ * Check the Python/C API docs for what type of reference a function returns.
+ *
+ *  - If it returns a "new reference", you're responsible to Py_DECREF() it.
+ *
+ *  - If it returns a "borrowed reference", you MUST NOT Py_DECREF() it.
+ *
+ *  - If a function "steals" a reference, you no longer are responsible for
+ *    Py_DECREF()ing it (someone else will do it for you at some point).
+ */
+
 /**
  * Initialize libsigrokdecode.
  *
@@ -263,9 +276,14 @@ int sigrokdecode_run_decoder(struct sigrokdecode_decoder *dec,
                return SIGROKDECODE_ERR_PYTHON; /* TODO: More specific error? */
        }
 
+       /*
+        * IMPORTANT: PyTuple_SetItem() "steals" a reference to py_value!
+        * That means we are no longer responsible for Py_DECREF()'ing it.
+        * It will automatically be free'd when the 'py_args' tuple is free'd.
+        */
        if (PyTuple_SetItem(py_args, 0, py_value) != 0) {
                PyErr_Print();
-               Py_DECREF(py_value);
+               Py_DECREF(py_value); /* TODO: Ref. stolen upon error? */
                Py_DECREF(py_args);
                Py_DECREF(py_func);
                Py_DECREF(py_mod);
@@ -274,7 +292,6 @@ int sigrokdecode_run_decoder(struct sigrokdecode_decoder *dec,
 
        if (!(py_res = PyObject_CallObject(py_func, py_args))) {
                PyErr_Print();
-               Py_DECREF(py_value);
                Py_DECREF(py_args);
                Py_DECREF(py_func);
                Py_DECREF(py_mod);
@@ -285,7 +302,6 @@ int sigrokdecode_run_decoder(struct sigrokdecode_decoder *dec,
                                         (Py_ssize_t *)outbuflen))) {
                PyErr_Print();
                Py_DECREF(py_res);
-               Py_DECREF(py_value);
                Py_DECREF(py_args);
                Py_DECREF(py_func);
                Py_DECREF(py_mod);
@@ -293,7 +309,6 @@ int sigrokdecode_run_decoder(struct sigrokdecode_decoder *dec,
        }
 
        Py_DECREF(py_res);
-       // Py_DECREF(py_value);
        Py_DECREF(py_args);
        Py_DECREF(py_func);
        Py_DECREF(py_mod);