Empty debug contexts are automatically cleaned up

CHANGELOG.md

@@ -39,6 +39,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   that can be deallocated independently of other graphs it is connected with.
 - `DynamicReader::on_disconnect` allows attaching a callback that is invoked
   once the final source `Dynamic` is dropped.
+- `Dynamic::instances()` returns the number of clones the dynamic has in
+  existence.
+- `Dynamic::readers()` returns the number of `DynamicReader`s for the dynamic in
+  existence.
 
 [99]: https://github.com/khonsulabs/cushy/issues/99
 

src/debug.rs

@@ -4,7 +4,7 @@ use std::fmt::Debug;
 
 use alot::OrderedLots;
 
-use crate::value::{Dynamic, DynamicReader, ForEach};
+use crate::value::{Dynamic, DynamicReader, ForEach, WeakDynamic};
 use crate::widget::{Children, MakeWidget, WidgetInstance};
 use crate::widgets::grid::{Grid, GridWidgets};
 use crate::window::Window;
@@ -83,6 +83,15 @@ impl DebugContext {
             .into_window()
             .titled("Cushy Debugger")
     }
+
+    /// Returns true if this debug context has no child sections or observed
+    /// values.
+    #[must_use]
+    pub fn is_empty(&self) -> bool {
+        self.section.map_ref(|section| {
+            section.children.map_ref(OrderedLots::len) + section.values.map_ref(OrderedLots::len)
+        }) == 0
+    }
 }
 
 impl Open for DebugContext {
@@ -98,6 +107,22 @@ impl Open for DebugContext {
     }
 }
 
+impl Drop for DebugContext {
+    fn drop(&mut self) {
+        // If the only two references are this context and the parent owning the
+        // child section, then we want to remove the section if nothing was
+        // added to it.
+        if self.section.instances() == 2 {
+            let section = self.section.lock();
+            if let Some(parent) = section.parent.clone() {
+                let label = section.label.clone();
+                drop(section);
+                DebugSection::remove_child_section(&parent, &label);
+            }
+        }
+    }
+}
+
 trait Observable: Send {
     fn label(&self) -> &str;
     fn alive(&self) -> bool;
@@ -132,6 +157,7 @@ struct DebugSection {
     children: Dynamic<OrderedLots<Dynamic<DebugSection>>>,
     values: Dynamic<OrderedLots<Box<dyn Observable>>>,
     widget: WidgetInstance,
+    parent: Option<WeakDynamic<DebugSection>>,
 }
 
 impl Default for DebugSection {
@@ -162,23 +188,13 @@ impl DebugSection {
 
         let parent = parent.map(Dynamic::downgrade);
         // Create a cleanup task to remove this section once it becomes empty.
-        if let Some(parent) = parent {
+        if let Some(parent) = parent.clone() {
             let label = label.clone();
             (&children, &values)
                 .for_each({
                     move |(children, values)| {
                         if children.is_empty() && values.is_empty() {
-                            if let Some(parent) = parent.upgrade() {
-                                let parent = parent.lock();
-                                let mut children = parent.children.lock();
-                                if let Some(index) =
-                                    children.iter().enumerate().find_map(|(index, child)| {
-                                        child.map_ref(|child| child.label == label).then_some(index)
-                                    })
-                                {
-                                    children.remove_by_index(index);
-                                }
-                            }
+                            Self::remove_child_section(&parent, &label);
                         }
                     }
                 })
@@ -204,6 +220,26 @@ impl DebugSection {
             children,
             values,
             widget,
+            parent,
+        }
+    }
+
+    fn remove_child_section(parent: &WeakDynamic<DebugSection>, label: &str) {
+        if let Some(parent) = parent.upgrade() {
+            let parent = parent.lock();
+            let mut children = parent.children.lock();
+            if let Some(index) = children.iter().enumerate().find_map(|(index, child)| {
+                child.map_ref(|child| child.label == label).then_some(index)
+            }) {
+                children.remove_by_index(index);
+            }
         }
     }
 }
+
+#[test]
+fn empty_child_clears_on_drop() {
+    let root = DebugContext::default();
+    drop(root.section("child"));
+    assert!(root.is_empty());
+}

src/value.rs

@@ -60,6 +60,30 @@ impl<T> Dynamic<T> {
         WeakDynamic::from(self)
     }
 
+    /// Returns the number [`Dynamic`]s that point to this same value.
+    ///
+    /// The returned count includes `self`.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if this value is already locked by the current
+    /// thread.
+    #[must_use]
+    pub fn instances(&self) -> usize {
+        Arc::strong_count(&self.0) - self.readers()
+    }
+
+    /// Returns the number of [`DynamicReader`]s for this value.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if this value is already locked by the current
+    /// thread.
+    #[must_use]
+    pub fn readers(&self) -> usize {
+        self.state().expect("deadlocked").readers
+    }
+
     /// Returns a new dynamic that has its contents linked with `self` by the
     /// pair of mapping functions provided.
     ///
@@ -2801,3 +2825,32 @@ fn compare_swap() {
     assert_eq!(dynamic.compare_swap(&2, 0), Ok(2));
     assert_eq!(dynamic.get(), 0);
 }
+
+#[test]
+fn ref_counts() {
+    let dynamic = Dynamic::new(1);
+    assert_eq!(dynamic.instances(), 1);
+
+    let second = dynamic.clone();
+    assert_eq!(dynamic.instances(), 2);
+
+    assert_eq!(dynamic.readers(), 0);
+    let reader = second.into_reader();
+    assert_eq!(dynamic.instances(), 1);
+    assert_eq!(dynamic.readers(), 1);
+
+    // Test that once the last instance is dropped that the reader is no longer
+    // connected and that on_disconnect gets invoked.
+    assert!(reader.connected());
+    let invoked = Dynamic::new(false);
+    reader.on_disconnect({
+        let invoked = invoked.clone();
+        move || {
+            invoked.set(true);
+        }
+    });
+    drop(dynamic);
+
+    assert!(invoked.get());
+    assert!(!reader.connected());
+}