1 files changed, 34 insertions, 0 deletions
diff --git a/library/std/src/sys/wasm/atomics/futex.rs b/library/std/src/sys/wasm/atomics/futex.rs
new file mode 100644
index 000000000..f4fbe9f48
--- /dev/null
+++ b/library/std/src/sys/wasm/atomics/futex.rs
@@ -0,0 +1,34 @@
+use crate::arch::wasm32;
+use crate::sync::atomic::AtomicU32;
+use crate::time::Duration;
+
+/// Wait for a futex_wake operation to wake us.
+///
+/// Returns directly if the futex doesn't hold the expected value.
+///
+/// Returns false on timeout, and true in all other cases.
+pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -> bool {
+    let timeout = timeout.and_then(|t| t.as_nanos().try_into().ok()).unwrap_or(-1);
+    unsafe {
+        wasm32::memory_atomic_wait32(
+            futex as *const AtomicU32 as *mut i32,
+            expected as i32,
+            timeout,
+        ) < 2
+    }
+}
+
+/// Wake up one thread that's blocked on futex_wait on this futex.
+///
+/// Returns true if this actually woke up such a thread,
+/// or false if no thread was waiting on this futex.
+pub fn futex_wake(futex: &AtomicU32) -> bool {
+    unsafe { wasm32::memory_atomic_notify(futex as *const AtomicU32 as *mut i32, 1) > 0 }
+}
+
+/// Wake up all threads that are waiting on futex_wait on this futex.
+pub fn futex_wake_all(futex: &AtomicU32) {
+    unsafe {
+        wasm32::memory_atomic_notify(futex as *const AtomicU32 as *mut i32, i32::MAX as u32);
+    }
+}