Make std::sys::wasm::futex consistent with unix::futex.

library/std/src/sys/wasm/atomics/futex.rs

@@ -3,19 +3,33 @@
 use crate::sync::atomic::AtomicU32;
 use crate::time::Duration;
 
-pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<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
     }
 }
 
-pub fn futex_wake(futex: &AtomicU32) {
+/// 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, 1);
+        wasm32::memory_atomic_notify(futex as *const AtomicU32 as *mut i32, i32::MAX as u32);
     }
 }