NEWS

NEWS.md

@@ -1,8 +1,8 @@
 # reticulate (development version)
 
 -   `py_iterator()` gains a `prefetch` argument, primarily to avoid deadlocks
-    in situations where a background thread is attempting to use the iterator 
-    while the main thread is fully blocked (as encountered in TensorFlow).
+    where the main thread is blocked, waiting for the iterator, which is waiting
+    to run on the main thread, as encountered in TensorFlow/Keras. (#1405).
 
 -   The knitr engine gains a `jupyter_compat` option, enabling
     reticulate to better match the behavior of Jupyter. When this chunk

inst/python/rpytools/generator.py

@@ -41,14 +41,12 @@ def _tend_queue(self, min_fetch=0):
 
         ## Prefetch and enqueue generator generated values.
 
-        # If we're not on the main thread, register a pending call to
-        # this function from the py main thread and return.
-        if (
-            not self._pending_tend_queue
-            and threading.current_thread() is not threading.main_thread()
-        ):
-            self._pending_tend_queue = True
-            rpycall.call_python_function_on_main_thread(self._tend_queue, min_fetch)
+        # If we're not on the main thread, make sure there is a pending call to
+        # this function from the main thread and return.
+        if threading.current_thread() is not threading.main_thread():
+            if not self._pending_tend_queue:
+                self._pending_tend_queue = True
+                rpycall.call_python_function_on_main_thread(self._tend_queue, min_fetch)
             return
 
         # We're on the main thread, call the generator and put values on the queue.