1 files changed, 98 insertions, 0 deletions
diff --git a/library/std/src/sys/wasm/thread.rs b/library/std/src/sys/wasm/thread.rs
new file mode 100644
index 00000000000..0a11896a004
--- /dev/null
+++ b/library/std/src/sys/wasm/thread.rs
@@ -0,0 +1,98 @@
+use crate::ffi::CStr;
+use crate::io;
+use crate::sys::{unsupported, Void};
+use crate::time::Duration;
+
+pub struct Thread(Void);
+
+pub const DEFAULT_MIN_STACK_SIZE: usize = 4096;
+
+impl Thread {
+    // unsafe: see thread::Builder::spawn_unchecked for safety requirements
+    pub unsafe fn new(_stack: usize, _p: Box<dyn FnOnce()>) -> io::Result<Thread> {
+        unsupported()
+    }
+
+    pub fn yield_now() {
+        // do nothing
+    }
+
+    pub fn set_name(_name: &CStr) {
+        // nope
+    }
+
+    #[cfg(not(target_feature = "atomics"))]
+    pub fn sleep(_dur: Duration) {
+        panic!("can't sleep");
+    }
+
+    #[cfg(target_feature = "atomics")]
+    pub fn sleep(dur: Duration) {
+        use crate::arch::wasm32;
+        use crate::cmp;
+
+        // Use an atomic wait to block the current thread artificially with a
+        // timeout listed. Note that we should never be notified (return value
+        // of 0) or our comparison should never fail (return value of 1) so we
+        // should always only resume execution through a timeout (return value
+        // 2).
+        let mut nanos = dur.as_nanos();
+        while nanos > 0 {
+            let amt = cmp::min(i64::MAX as u128, nanos);
+            let mut x = 0;
+            let val = unsafe { wasm32::i32_atomic_wait(&mut x, 0, amt as i64) };
+            debug_assert_eq!(val, 2);
+            nanos -= amt;
+        }
+    }
+
+    pub fn join(self) {
+        match self.0 {}
+    }
+}
+
+pub mod guard {
+    pub type Guard = !;
+    pub unsafe fn current() -> Option<Guard> {
+        None
+    }
+    pub unsafe fn init() -> Option<Guard> {
+        None
+    }
+}
+
+// This is only used by atomics primitives when the `atomics` feature is
+// enabled. In that mode 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.
+#[cfg(target_feature = "atomics")]
+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::arch::wasm32::unreachable());
+                match NEXT_ID.compare_exchange(cur, next, SeqCst, SeqCst) {
+                    Ok(_) => break next,
+                    Err(i) => cur = i,
+                }
+            };
+        }
+        MY_ID
+    }
+}