Make NopReceiver.ready() respond to close() method

The ready() method was not terminating when close() was called, causing
it to hang indefinitely. This fix ensures ready() returns False when
the receiver is closed.

Signed-off-by: Elzbieta Kotulska <[email protected]>

Author: ela-kotulska-frequenz

RELEASE_NOTES.md

@@ -14,4 +14,4 @@
 
 ## Bug Fixes
 
-<!-- Here goes notable bug fixes that are worth a special mention or explanation -->
+- Fix `NopReceiver.ready()` to properly terminate when receiver is closed.

src/frequenz/channels/experimental/_nop_receiver.py

@@ -20,7 +20,7 @@ class NopReceiver(Receiver[ReceiverMessageT_co]):
 
     def __init__(self) -> None:
         """Initialize this instance."""
-        self._closed: bool = False
+        self._ready_future: asyncio.Future[bool] = asyncio.Future()
 
     @override
     async def ready(self) -> bool:
@@ -29,10 +29,9 @@ async def ready(self) -> bool:
         Returns:
             Whether the receiver is still active.
         """
-        if self._closed:
+        if self._ready_future.done():
             return False
-        await asyncio.Future()
-        return False
+        return await self._ready_future
 
     @override
     def consume(self) -> ReceiverMessageT_co:  # noqa: DOC503 (raised indirectly)
@@ -47,11 +46,12 @@ def consume(self) -> ReceiverMessageT_co:  # noqa: DOC503 (raised indirectly)
             ReceiverStoppedError: If the receiver stopped producing messages.
             ReceiverError: If there is some problem with the underlying receiver.
         """
-        if self._closed:
+        if self._ready_future.done():
             raise ReceiverStoppedError(self)
         raise ReceiverError("`consume()` must be preceded by a call to `ready()`", self)
 
     @override
     def close(self) -> None:
         """Stop the receiver."""
-        self._closed = True
+        if not self._ready_future.done():
+            self._ready_future.set_result(False)

tests/experimental/test_nop_receiver.py

@@ -38,3 +38,28 @@ async def test_consuming_raises() -> None:
     receiver.close()
     with pytest.raises(ReceiverStoppedError):
         receiver.consume()
+
+
+async def test_close_method_effect_on_ready() -> None:
+    """Test `ready()` terminates when the receiver is closed.
+
+    When the receiver is closed, `ready()` should return False.
+    This test verifies that:
+    1. `ready()` returns False immediately after `close()` is called
+    2. `ready()` and `close()` can be called multiple times
+    """
+    receiver = NopReceiver[int]()
+
+    # Create a task that waits for the receiver to be ready.
+    task = asyncio.create_task(receiver.ready())
+
+    # Wait for the task to start.
+    await asyncio.sleep(0.1)
+
+    # Close the receiver and wait for the task to complete.
+    receiver.close()
+    assert await asyncio.wait_for(task, timeout=0.1) is False
+
+    # Second call to `close()` or `ready()` should not raise an error.
+    receiver.close()
+    assert await asyncio.wait_for(receiver.ready(), timeout=0.1) is False