diff --git a/vm/src/sync.rs b/vm/src/sync.rs
new file mode 100644
index 0000000..82839b3
--- /dev/null
+++ b/vm/src/sync.rs
@@ -0,0 +1,46 @@
+// Copyright 2021, The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Synchronisation utilities.
+
+use std::sync::{Arc, Condvar, Mutex};
+
+/// A flag which one thread can use to notify other threads when a condition becomes true. This is
+/// something like a single-use binary semaphore.
+#[derive(Clone, Debug)]
+pub struct AtomicFlag {
+    state: Arc<(Mutex<bool>, Condvar)>,
+}
+
+impl Default for AtomicFlag {
+    #[allow(clippy::mutex_atomic)]
+    fn default() -> Self {
+        Self { state: Arc::new((Mutex::new(false), Condvar::new())) }
+    }
+}
+
+#[allow(clippy::mutex_atomic)]
+impl AtomicFlag {
+    /// Wait until the flag is set.
+    pub fn wait(&self) {
+        let _flag = self.state.1.wait_while(self.state.0.lock().unwrap(), |flag| !*flag).unwrap();
+    }
+
+    /// Set the flag, and notify all waiting threads.
+    pub fn raise(&self) {
+        let mut flag = self.state.0.lock().unwrap();
+        *flag = true;
+        self.state.1.notify_all();
+    }
+}