1 files changed, 54 insertions, 0 deletions
diff --git a/p2p/src/net/slots.rs b/p2p/src/net/slots.rs
new file mode 100644
index 0000000..99f0a78
--- /dev/null
+++ b/p2p/src/net/slots.rs
@@ -0,0 +1,54 @@
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+use karyons_core::async_utils::CondWait;
+
+/// Manages available inbound and outbound slots.
+pub struct ConnectionSlots {
+    /// A condvar for notifying when a slot become available.
+    signal: CondWait,
+    /// The number of occupied slots
+    slots: AtomicUsize,
+    /// The maximum number of slots.
+    max_slots: usize,
+}
+
+impl ConnectionSlots {
+    /// Creates a new ConnectionSlots
+    pub fn new(max_slots: usize) -> Self {
+        Self {
+            signal: CondWait::new(),
+            slots: AtomicUsize::new(0),
+            max_slots,
+        }
+    }
+
+    /// Returns the number of occupied slots
+    pub fn load(&self) -> usize {
+        self.slots.load(Ordering::SeqCst)
+    }
+
+    /// Increases the occupied slots by one.
+    pub fn add(&self) {
+        self.slots.fetch_add(1, Ordering::SeqCst);
+    }
+
+    /// Decreases the occupied slots by one and notifies the waiting signal
+    /// to start accepting/connecting new connections.
+    pub async fn remove(&self) {
+        self.slots.fetch_sub(1, Ordering::SeqCst);
+        if self.slots.load(Ordering::SeqCst) < self.max_slots {
+            self.signal.signal().await;
+        }
+    }
+
+    /// Waits for a slot to become available.
+    pub async fn wait_for_slot(&self) {
+        if self.slots.load(Ordering::SeqCst) < self.max_slots {
+            return;
+        }
+
+        // Wait for a signal
+        self.signal.wait().await;
+        self.signal.reset().await;
+    }
+}