Convert to Resources, and other API cleanups. (#46)

* Convert to Resources, and other API cleanups.

 - Convert to resources. Use resources instead of `u32`s, remove
   drop functions, `this` arguments, and rename `subscribe-to-*`
   to just `subscribe`, as discussed in WebAssembly/wasi-poll#21.

 - Merge wasi-poll into wasi-io. These two proposals are closely
   related to each other, so it makes sense to have them together.

 - While here, tidy up the poll API, incorporating ideas discussed
   in WebAssembly/wasi-poll#22:

   - Rename `poll-oneoff` to `poll-list`, and add a `poll-one`.

   - Change `poll-oneoff`'s return type from `list<bool>` to `list<u32>`,
     because in the common case, this should allow it to create much
     smaller allocations.

* Update to WebAssembly/wit-abi-up-to-date@v14.

* Remove the wit-deps check now that we have no dependencies.

* Fix more references to `poll-oneoff`.

* Mark `poll` arguments as borrowed.

* Update to wit-abi-up-to-date@v15.

Author: sunfishcode

.github/workflows/main.yml

@@ -10,12 +10,5 @@ jobs:
     name: Check ABI files are up-to-date
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
-    - name: ensure `./wit/deps` are in sync
-      run: |
-        curl -Lo 'wit-deps' https://github.com/bytecodealliance/wit-deps/releases/download/v0.3.2/wit-deps-x86_64-unknown-linux-musl
-        chmod +x wit-deps
-        ./wit-deps lock --check
-    - uses: WebAssembly/wit-abi-up-to-date@v13
-      with:
-        wit-abi-tag: wit-abi-0.11.0
+    - uses: actions/checkout@v3
+    - uses: WebAssembly/wit-abi-up-to-date@v15

README.md

@@ -69,7 +69,7 @@ types, `input-stream`, and `output-stream`, which support `read` and
 
            // If we didn't get any data promptly, wait for it.
            if data.len() == 0 {
-               let _ = poll_oneoff(&wait_input[..]);
+               let _ = poll_list(&wait_input[..]);
                (data, eos) = input.read(BUFFER_LEN)?;
            }
 
@@ -79,7 +79,7 @@ types, `input-stream`, and `output-stream`, which support `read` and
 
                // If we didn't put any data promptly, wait for it.
                if num_written == 0 {
-                   let _ = poll_oneoff(&wait_output[..]);
+                   let _ = poll_list(&wait_output[..]);
                    num_written = output.write(remaining)?;
                }
 
@@ -108,7 +108,7 @@ types, `input-stream`, and `output-stream`, which support `read` and
 
            // If we didn't get any data promptly, wait for it.
            if num_copied == 0 {
-               let _ = poll_oneoff(&wait_input[..]);
+               let _ = poll_list(&wait_input[..]);
            }
        }
        Ok(())

example-world.md

@@ -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<borrow<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: borrow<pollable>)
+}