allow registration of variable watchers

1 files changed, 61 insertions, 0 deletions

diff --git a/src/run/var/watch.rs b/src/run/var/watch.rs
new file mode 100644
index 0000000..22ac638
--- /dev/null
+++ b/src/run/var/watch.rs
@@ -0,0 +1,61 @@
+use std::{
+    hash::Hash,
+    sync::{Arc, Weak, atomic::AtomicU32},
+};
+
+#[derive(Clone)]
+pub struct WatchId {
+    id: u32,
+    count: Arc<()>,
+}
+
+#[derive(Clone)]
+pub struct WeakWatchId {
+    id: u32,
+    count: Weak<()>,
+}
+
+impl PartialEq for WeakWatchId {
+    fn eq(&self, other: &Self) -> bool {
+        self.id == other.id
+    }
+}
+
+impl Eq for WeakWatchId {}
+
+impl Hash for WeakWatchId {
+    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
+        self.id.hash(state);
+    }
+}
+
+impl WatchId {
+    pub(super) fn new() -> Self {
+        static GEN: AtomicU32 = AtomicU32::new(0);
+        Self {
+            id: GEN.fetch_add(1, std::sync::atomic::Ordering::SeqCst),
+            count: Arc::new(()),
+        }
+    }
+
+    pub(super) fn weak(&self) -> WeakWatchId {
+        WeakWatchId {
+            id: self.id,
+            count: Arc::downgrade(&self.count),
+        }
+    }
+}
+
+impl WeakWatchId {
+    pub fn is_dead(&self) -> bool {
+        self.count.upgrade().is_none()
+    }
+}
+
+pub struct WatchState {
+    /// if set, essentially always dirty
+    pub special: bool,
+
+    /// has the set of watched variables changed?
+    pub dirty: bool,
+}