Update to resources.

wit/poll.wit

@@ -0,0 +1,34 @@
+package wasi:io
+
+/// A poll API intended to let users wait for I/O events on multiple handles
+/// at once.
+interface poll {
+    /// A "pollable" handle.
+    resource pollable
+
+    /// Poll for completion on a set of pollables.
+    ///
+    /// This function takes a list of pollables, which identify I/O sources of
+    /// interest, and waits until one or more of the events is ready for I/O.
+    ///
+    /// The result `list<u32>` contains one or more indices of handles in the
+    /// argument list that is ready for I/O.
+    ///
+    /// If the list contains more elements than can be indexed with a `u32`
+    /// value, this function traps.
+    ///
+    /// A timeout can be implemented by adding a pollable from the
+    /// wasi-clocks API to the list.
+    ///
+    /// This function does not return a `result`; polling in itself does not
+    /// do any I/O so it doesn't fail. If any of the I/O sources identified by
+    /// the pollables has an error, it is indicated by marking the source as
+    /// being reaedy for I/O.
+    poll-list: func(in: list<pollable>) -> list<u32>
+
+    /// Poll for completion on a single pollable.
+    ///
+    /// This function is similar to `poll-list`, but operates on only a single
+    /// pollable. When it returns, the handle is ready for I/O.
+    poll-one: func(in: pollable)
+}