Add some comments and fixes to the examples.

Author: ZeroIntensity

peps/pep-0788.rst

@@ -444,16 +444,19 @@ held. Any future finalizer that wanted to acquire the lock would be deadlocked!
     {
         assert(PyThreadState_GetUnchecked() != NULL);
         PyInterpreterState *interp = PyInterpreterState_Hold();
+        /* Temporarily make this thread non-daemon to ensure that the
+           lock is released. */
         if (PyThreadState_Ensure(interp) < 0) {
-            PyErr_SetString(PyExc_RuntimeError, "interpreter is shutting down");
+            PyErr_SetString(PyExc_PythonFinalizationError,
+                            "interpreter is shutting down");
             return NULL;
         }
 
         Py_BEGIN_ALLOW_THREADS;
         acquire_some_lock();
         Py_END_ALLOW_THREADS;
 
-        /* Do something with the lock */
+        /* Do something while holding the lock */
         // ...
 
         release_some_lock();
@@ -525,6 +528,7 @@ This is the same code, updated to use the new functions:
 
         PyInterpreterState *interp = PyInterpreterState_Hold();
         if (PyThread_start_joinable_thread(thread_func, interp, &ident, &handle) < 0) {
+            PyInterpreterState_Release(interp);
             return NULL;
         }
         Py_BEGIN_ALLOW_THREADS