Rollup merge of rust-lang#96206 - m-ou-se:wasm-futex-locks, r=alexcrichton

Use sys::unix::locks::futex* on wasm+atomics.

This removes the wasm-specific lock implementations and instead re-uses the implementations from sys::unix.

Tracking issue: rust-lang#93740

cc `@alexcrichton`

Author: Dylan-DPC

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

@@ -3,19 +3,33 @@ use crate::convert::TryInto;
 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);
     }
 }

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

@@ -53,37 +53,3 @@ pub mod guard {
         None
     }
 }
-
-// We currently just use our own thread-local to store our
-// current thread's ID, and then we lazily initialize it to something allocated
-// from a global counter.
-pub fn my_id() -> u32 {
-    use crate::sync::atomic::{AtomicU32, Ordering::SeqCst};
-
-    static NEXT_ID: AtomicU32 = AtomicU32::new(0);
-
-    #[thread_local]
-    static mut MY_ID: u32 = 0;
-
-    unsafe {
-        // If our thread ID isn't set yet then we need to allocate one. Do so
-        // with with a simple "atomically add to a global counter" strategy.
-        // This strategy doesn't handled what happens when the counter
-        // overflows, however, so just abort everything once the counter
-        // overflows and eventually we could have some sort of recycling scheme
-        // (or maybe this is all totally irrelevant by that point!). In any case
-        // though we're using a CAS loop instead of a `fetch_add` to ensure that
-        // the global counter never overflows.
-        if MY_ID == 0 {
-            let mut cur = NEXT_ID.load(SeqCst);
-            MY_ID = loop {
-                let next = cur.checked_add(1).unwrap_or_else(|| crate::process::abort());
-                match NEXT_ID.compare_exchange(cur, next, SeqCst, SeqCst) {
-                    Ok(_) => break next,
-                    Err(i) => cur = i,
-                }
-            };
-        }
-        MY_ID
-    }
-}