scaffold a scheduler

crates/wasi-c2/src/sched.rs

@@ -0,0 +1,20 @@
+use crate::Error;
+
+pub trait WasiSched {
+    // XXX poll oneoff needs args and results.
+    fn poll_oneoff(&self) -> Result<(), Error>;
+    fn sched_yield(&self) -> Result<(), Error>;
+}
+
+#[derive(Default)]
+pub struct SyncSched {}
+
+impl WasiSched for SyncSched {
+    fn poll_oneoff(&self) -> Result<(), Error> {
+        todo!()
+    }
+    fn sched_yield(&self) -> Result<(), Error> {
+        std::thread::yield_now();
+        Ok(())
+    }
+}