# UNDF: UNDF-2026-000000335
--- a/lib/wasix/src/os/task/thread.rs
+++ b/lib/wasix/src/os/task/thread.rs
@@ -238,7 +238,9 @@ pub struct WasiThreadInner {
     pub(crate) status: Arc<OwnedTaskStatus>,
     /// Signals are used to indicate certain states to the thread
-    signals: Mutex<(Vec<Signal>, Vec<Waker>)>,
+    /// Using a u64 bitmask instead of Vec<Signal> — Signal values are 1..=31,
+    /// so bit N represents signal N. O(1) insert, O(1) contains, O(1) test.
+    signals: Mutex<(u64, Vec<Waker>)>,
 }

@@ -268,7 +270,7 @@ impl WasiThreadInner {
             status: Arc::new(OwnedTaskStatus::new(TaskStatus::Pending)),
-            signals: Mutex::new((Vec::new(), Vec::new())),
+            signals: Mutex::new((0u64, Vec::new())),
         }
     }

@@ -345,10 +347,8 @@ impl WasiThread {
         let mut guard = self.state.signals.lock().unwrap();
-        if !guard.0.contains(&signal) {
-            guard.0.push(signal);
-        }
+        // Set bit for this signal — O(1) insert with automatic dedup
+        guard.0 |= 1u64 << (signal as u32);
         guard.1.drain(..).for_each(|w| w.wake());
     }

@@ -358,10 +358,10 @@ impl WasiThread {
     pub fn has_signal(&self, signals: &[Signal]) -> bool {
         let guard = self.state.signals.lock().unwrap();
-        for s in guard.0.iter() {
-            if signals.contains(s) {
-                return true;
-            }
-        }
-        false
+        // Build query bitmask in O(|signals|), then AND in O(1)
+        let query_mask: u64 = signals.iter().fold(0u64, |m, s| m | (1u64 << (*s as u32)));
+        guard.0 & query_mask != 0
     }

@@ -390,7 +390,7 @@ impl WasiThread {
     pub fn pop_signals_or_subscribe(&self, waker: &Waker) -> Option<Vec<Signal>> {
         let mut guard = self.state.signals.lock().unwrap();
-        if guard.0.is_empty() {
+        if guard.0 == 0 {
             // ...
         }
         // Convert bitmask back to Vec<Signal> for consumption
-        Some(std::mem::take(&mut guard.0))
+        let mask = std::mem::replace(&mut guard.0, 0u64);
+        Some((0u32..64).filter(|b| mask & (1u64 << b) != 0)
+            .filter_map(|b| Signal::try_from(b as i32).ok())
+            .collect())
     }