Skip checking if the eval context is active if we're in the background thread of async execution.

Signed-off-by: Rostan Tabet <rtabet@nvidia.com>

Author: rostan-t

dali/python/nvidia/dali/experimental/dynamic/_async.py

@@ -78,6 +78,7 @@ def __init__(self):
         self._queue = queue.SimpleQueue[Optional[_Future]]()
         self._thread: Optional[threading.Thread] = None
         self._event = threading.Event()
+        self._main_thread = threading.current_thread()
 
     def _worker(self):
         while True:

dali/python/nvidia/dali/experimental/dynamic/_eval_context.py

@@ -210,14 +210,16 @@ def _is_current(self) -> bool:
         return self is _tls.default.get(current_device_id)
 
     def __enter__(self):
-        if not self._lock.acquire(blocking=False):
+        skip_lock = self._is_in_background_thread()
+        if not skip_lock and not self._lock.acquire(blocking=False):
             raise RuntimeError("An EvalContext cannot be active in two threads simultaneously.")
         try:
             _tls.stack.append(self)
             if self._device:
                 self._device.__enter__()
         except Exception:
-            self._lock.release()
+            if not skip_lock:
+                self._lock.release()
             raise
         return self
 
@@ -235,7 +237,8 @@ def __exit__(self, exc_type, exc_value, traceback):
             if self._device:
                 self._device.__exit__(exc_type, exc_value, traceback)
         finally:
-            self._lock.release()
+            if not self._is_in_background_thread():
+                self._lock.release()
 
     def evaluate_all(self):
         """Evaluates all pending invocations."""