: 'configure' should merge to global config not set

hyperactor/src/attrs.rs

@@ -556,6 +556,15 @@ impl Attrs {
     pub(crate) fn get_value_by_name(&self, name: &'static str) -> Option<&dyn SerializableValue> {
         self.values.get(name).map(|b| b.as_ref())
     }
+
+    /// Merge all attributes from `other` into this set, consuming
+    /// `other`.
+    ///
+    /// For each key in `other`, moves its value into `self`,
+    /// overwriting any existing value for the same key.
+    pub(crate) fn merge(&mut self, other: Attrs) {
+        self.values.extend(other.values);
+    }
 }
 
 impl Clone for Attrs {

hyperactor/src/config/global.rs

@@ -440,6 +440,24 @@ pub fn try_get_cloned<T: AttrValue>(key: Key<T>) -> Option<T> {
     key.default().cloned()
 }
 
+/// Construct a [`Layer`] for the given [`Source`] using the provided
+/// `attrs`.
+///
+/// Used by [`set`] and [`create_or_merge`] when installing a new
+/// configuration layer.
+fn make_layer(source: Source, attrs: Attrs) -> Layer {
+    match source {
+        Source::File => Layer::File(attrs),
+        Source::Env => Layer::Env(attrs),
+        Source::Runtime => Layer::Runtime(attrs),
+        Source::TestOverride => Layer::TestOverride {
+            attrs,
+            stacks: HashMap::new(),
+        },
+        Source::ClientOverride => Layer::ClientOverride(attrs),
+    }
+}
+
 /// Insert or replace a configuration layer for the given source.
 ///
 /// If a layer with the same [`Source`] already exists, its
@@ -457,16 +475,34 @@ pub fn set(source: Source, attrs: Attrs) {
     if let Some(l) = g.ordered.iter_mut().find(|l| layer_source(l) == source) {
         *layer_attrs_mut(l) = attrs;
     } else {
-        g.ordered.push(match source {
-            Source::File => Layer::File(attrs),
-            Source::Env => Layer::Env(attrs),
-            Source::Runtime => Layer::Runtime(attrs),
-            Source::TestOverride => Layer::TestOverride {
-                attrs,
-                stacks: HashMap::new(),
-            },
-            Source::ClientOverride => Layer::ClientOverride(attrs),
-        });
+        g.ordered.push(make_layer(source, attrs));
+    }
+    g.ordered.sort_by_key(|l| priority(layer_source(l))); // TestOverride < Runtime < Env < File < ClientOverride
+}
+
+/// Insert or update a configuration layer for the given [`Source`].
+///
+/// If a layer with the same [`Source`] already exists, its attributes
+/// are **updated in place**: all keys present in `attrs` are absorbed
+/// into the existing layer, overwriting any previous values for those
+/// keys while leaving all other keys in that layer unchanged.
+///
+/// If no layer for `source` exists yet, this behaves like [`set`]: a
+/// new layer is created with the provided `attrs`.
+///
+/// This is useful for incremental / additive updates (for example,
+/// runtime configuration driven by a Python API), where callers want
+/// to change a subset of keys without discarding previously installed
+/// values in the same layer.
+///
+/// By contrast, [`set`] replaces the entire layer for `source` with
+/// `attrs`, discarding any existing values in that layer.
+pub fn create_or_merge(source: Source, attrs: Attrs) {
+    let mut g = LAYERS.write().unwrap();
+    if let Some(layer) = g.ordered.iter_mut().find(|l| layer_source(l) == source) {
+        layer_attrs_mut(layer).merge(attrs);
+    } else {
+        g.ordered.push(make_layer(source, attrs));
     }
     g.ordered.sort_by_key(|l| priority(layer_source(l))); // TestOverride < Runtime < Env < File < ClientOverride
 }
@@ -1206,4 +1242,37 @@ mod tests {
         assert!(priority(Env) < priority(File));
         assert!(priority(File) < priority(ClientOverride));
     }
+
+    #[test]
+    fn test_create_or_merge_runtime_merges_keys() {
+        let _lock = lock();
+        reset_to_defaults();
+
+        // Seed Runtime with one key.
+        let mut rt = Attrs::new();
+        rt[MESSAGE_TTL_DEFAULT] = 10;
+        set(Source::Runtime, rt);
+
+        // Now update Runtime with a different key via
+        // `create_or_merge`.
+        let mut update = Attrs::new();
+        update[MESSAGE_ACK_EVERY_N_MESSAGES] = 123;
+        create_or_merge(Source::Runtime, update);
+
+        // Both keys should now be visible from Runtime.
+        assert_eq!(get(MESSAGE_TTL_DEFAULT), 10);
+        assert_eq!(get(MESSAGE_ACK_EVERY_N_MESSAGES), 123);
+    }
+
+    #[test]
+    fn test_create_or_merge_runtime_creates_layer_if_missing() {
+        let _lock = lock();
+        reset_to_defaults();
+
+        let mut rt = Attrs::new();
+        rt[MESSAGE_TTL_DEFAULT] = 42;
+        create_or_merge(Source::Runtime, rt);
+
+        assert_eq!(get(MESSAGE_TTL_DEFAULT), 42);
+    }
 }

hyperactor_mesh/src/bootstrap.rs

@@ -96,7 +96,7 @@ declare_attrs! {
     /// piping) or via [`StreamFwder`] when piping is active.
     @meta(CONFIG = ConfigAttr {
         env_name: Some("HYPERACTOR_MESH_ENABLE_LOG_FORWARDING".to_string()),
-        py_name: None,
+        py_name: Some("enable_log_forwarding".to_string()),
     })
     pub attr MESH_ENABLE_LOG_FORWARDING: bool = false;
 
@@ -121,7 +121,7 @@ declare_attrs! {
     ///   buffer used for peeking—independent of file capture.
     @meta(CONFIG = ConfigAttr {
         env_name: Some("HYPERACTOR_MESH_ENABLE_FILE_CAPTURE".to_string()),
-        py_name: None,
+        py_name: Some("enable_file_capture".to_string()),
     })
     pub attr MESH_ENABLE_FILE_CAPTURE: bool = false;
 
@@ -130,7 +130,7 @@ declare_attrs! {
     /// pipes. Default: 100
     @meta(CONFIG = ConfigAttr {
         env_name: Some("HYPERACTOR_MESH_TAIL_LOG_LINES".to_string()),
-        py_name: None,
+        py_name: Some("tail_log_lines".to_string()),
     })
     pub attr MESH_TAIL_LOG_LINES: usize = 0;
 

monarch_hyperactor/src/config.rs

@@ -97,7 +97,7 @@ fn set_global_config<T: AttrValue + Debug>(key: &'static dyn ErasedKey, value: T
     let key = key.downcast_ref().expect("cannot fail");
     let mut attrs = Attrs::new();
     attrs.set(key.clone(), value);
-    hyperactor::config::global::set(Source::Runtime, attrs);
+    hyperactor::config::global::create_or_merge(Source::Runtime, attrs);
     Ok(())
 }
 

python/monarch/_rust_bindings/monarch_hyperactor/config.pyi

@@ -25,5 +25,8 @@ def reload_config_from_env() -> None:
 
 def configure(
     default_transport: ChannelTransport = ChannelTransport.Unix,
+    enable_log_forwarding: bool = False,
+    enable_file_capture: bool = False,
+    tail_log_lines: int = 0,
 ) -> None: ...
 def get_configuration() -> Dict[str, Any]: ...

python/tests/test_config.py

@@ -39,3 +39,14 @@ def test_get_set_transport() -> None:
 def test_nonexistent_config_key() -> None:
     with pytest.raises(ValueError):
         configure(does_not_exist=42)  # type: ignore
+
+
+def test_get_set_multiple() -> None:
+    configure(default_transport=ChannelTransport.TcpWithLocalhost)
+    configure(enable_log_forwarding=True, enable_file_capture=True, tail_log_lines=100)
+    config = get_configuration()
+
+    assert config["enable_log_forwarding"]
+    assert config["enable_file_capture"]
+    assert config["tail_log_lines"] == 100
+    assert config["default_transport"] == ChannelTransport.TcpWithLocalhost