YieldFrame: pause wasm environment till end of frame

crates/editor/src/main.rs

@@ -7,8 +7,17 @@ use crate::go_builder::GoBuilder;
 mod go_builder;
 
 fn main() -> VResult<()> {
-    let builder = GoBuilder::new(&PathBuf::from("example_project"))?;
+    let builder = GoBuilder::new(
+        &PathBuf::from("example_project"))?;
     let wasm = builder.build()?;
-    player::run_entry_point(&wasm)?;
+    let mut executor = player::Executor::new(&wasm)?;
+
+    while executor.is_running() {
+        println!("update started");
+        executor.update();
+        println!("update completed");
+        executor.get_error()?;
+    }
+
     Ok(())
 }

crates/player/src/engine_api.rs

@@ -0,0 +1,31 @@
+use std::fmt::Display;
+
+use viperid::VResult;
+use wasmi::{core::{HostError, Trap}, Caller, Linker};
+
+use crate::executor::ExecutorState;
+
+pub(crate) fn integrate(linker: &mut Linker<ExecutorState>) -> VResult<()> {
+    linker.func_wrap("viperid", "YieldFrame", yield_frame)?;
+
+    Ok(())
+}
+
+fn yield_frame(caller: Caller<ExecutorState>) -> Result<(), Trap> {
+    Err(Trap::from(YieldFrame {}))
+}
+
+#[derive(Debug)]
+pub(crate) struct YieldFrame {
+
+}
+
+impl Display for YieldFrame {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str("<device wants to display a frame>")
+    }
+}
+
+impl HostError for YieldFrame {
+
+}

crates/player/src/executor.rs

@@ -1,9 +1,16 @@
+use std::{fmt::Display, mem};
+
 use viperid::VResult;
-use wasmi::{Engine, Linker, Module, Store};
+use wasmi::{core::{HostError, Trap}, Engine, Linker, Module, Store, TypedFunc, TypedResumableCall, TypedResumableInvocation};
 
-use crate::wasi::{self, StockWasi};
+use crate::{engine_api::{self, YieldFrame}, wasi::{self, StockWasi}};
 
-struct ExecutorState {
+pub struct Executor {
+    store: Store<ExecutorState>,
+    resumable: Resumable
+}
+
+pub(crate) struct ExecutorState {
     wasi: wasi::StockWasi
 }
 
@@ -16,7 +23,9 @@ impl ExecutorState {
     }
 }
 
-pub fn run_entry_point(wasm: &[u8]) -> VResult<()> {
+
+impl Executor { 
+    pub fn new(wasm: &[u8]) -> VResult<Self> {
         let engine = Engine::default();
 
         let module = Module::new(&engine, wasm)?;
@@ -25,13 +34,94 @@ pub fn run_entry_point(wasm: &[u8]) -> VResult<()> {
 
         let mut linker = <Linker<ExecutorState>>::new(&engine);
         wasi::integrate(&mut linker, |hs| &mut hs.wasi)?;
+        engine_api::integrate(&mut linker);
 
         let instance = linker
             .instantiate(&mut store, &module)?
             .start(&mut store)?;
 
         let main = instance.get_typed_func::<(), ()>(&store, "_start")?;
-    main.call(&mut store, ())?;
 
+        Ok(Executor {
+            store,
+            resumable: Resumable::Unstarted(main)
+        })
+    }
+
+    pub fn is_running(&self) -> bool {
+        self.resumable.is_running()
+    }
+
+    pub fn get_error(&self) -> VResult<()> {
+        if let Err(e) = self.resumable.get_error() {
+            anyhow::bail!("executor error: {}", e);
+        }
         Ok(())
     }
+
+    pub fn update(&mut self) {
+        let mut tmp = Resumable::Failed(wasmi::Error::Trap(Trap::new("unexpected crash during update")));
+        mem::swap(&mut tmp, &mut self.resumable);
+        let mut tmp2 = tmp.resume(&mut self.store);
+        mem::swap(&mut tmp2, &mut self.resumable);
+    }
+}
+
+enum Resumable {
+    Unstarted(TypedFunc<(), ()>),
+    Paused(TypedResumableInvocation<()>),
+    Failed(wasmi::Error),
+    Completed(())
+}
+
+
+impl Resumable {
+    pub fn resume(self, store: &mut Store<ExecutorState>) -> Resumable {
+        let result: Result<TypedResumableCall<()>, wasmi::Error> = match self {
+            Resumable::Failed(f) => return Resumable::Failed(f),
+            Resumable::Completed(c) => return Resumable::Completed(c),
+            Resumable::Unstarted(u) => {
+                match u.call_resumable(store, ()) {
+                    Ok(o) => Ok(o),
+                    Err(e) => Err(wasmi::Error::Trap(e))
+                }
+            }
+            Resumable::Paused(p) => {
+                let trap = p.host_error();
+
+                if let Some(_) = trap.downcast_ref::<YieldFrame>() {
+                    p.resume(store, &[])
+                } else {
+                    Err(wasmi::Error::Trap(Trap::new(format!("unexpected host error: {}", trap))))
+                }
+            }
+        };
+
+        match result {
+            Ok(o) => match o {
+                TypedResumableCall::Finished(f) => Resumable::Completed(f),
+                TypedResumableCall::Resumable(p) => Resumable::Paused(p)
+            }
+            Err(e) => Resumable::Failed(e),
+        }
+    }
+    
+    fn is_running(&self) -> bool {
+        match self {
+            Resumable::Unstarted(_) => true,
+            Resumable::Paused(_) => true,
+            Resumable::Failed(_) => false,
+            Resumable::Completed(_) => false
+        }
+    }
+    
+    fn get_error(&self) -> Result<(), &wasmi::Error> {
+        match self {
+            Resumable::Unstarted(_) => (),
+            Resumable::Paused(_) => (),
+            Resumable::Failed(e) => return Err(e),
+            Resumable::Completed(_) => ()
+        };
+        Ok(())
+    }
+}

crates/player/src/lib.rs

@@ -1,4 +1,5 @@
+mod engine_api;
 mod executor;
 mod wasi;
 
-pub use executor::run_entry_point;
+pub use executor::Executor;

example_project/.gitignore

@@ -0,0 +1 @@
+build/

example_project/go.work

@@ -0,0 +1 @@
+go 1.21.5

example_project/main.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"fmt"
-	"runtime/debug"
 )
 
 func main() {
@@ -10,7 +9,13 @@ func main() {
 	for {
 		fmt.Printf("Hello! %d", count)
 		count++
+		/*
 			debug.PrintStack()
-		panic("pizza!")
+		*/
+		YieldFrame()
 	}
 }
+
+//go:wasmimport viperid YieldFrame
+//go:noescape
+func YieldFrame()