Fix sequential awaited calls in Asyncify runtimes

packages/quickjs-emscripten-core/src/runtime-asyncify.ts

@@ -2,6 +2,7 @@ import type {
   QuickJSAsyncEmscriptenModule,
   QuickJSAsyncFFI,
   JSContextPointer,
+  JSContextPointerPointer,
   JSRuntimePointer,
 } from "@jitl/quickjs-ffi-types"
 import { QuickJSAsyncContext } from "./context-asyncify"
@@ -21,6 +22,7 @@ import type {
 } from "./types"
 import { intrinsicsToFlags } from "./types"
 import { Lifetime } from "./lifetime"
+import type { ExecutePendingJobsResult } from "./runtime"
 
 export class QuickJSAsyncRuntime extends QuickJSRuntime {
   declare public context: QuickJSAsyncContext | undefined
@@ -92,4 +94,27 @@ export class QuickJSAsyncRuntime extends QuickJSRuntime {
   public override setMaxStackSize(stackSize: number): void {
     return super.setMaxStackSize(stackSize)
   }
+
+  /**
+   * Asyncified version of {@link QuickJSRuntime.executePendingJobs}.
+   *
+   * Pending jobs may call an asyncified host function, so the synchronous
+   * version cannot safely drive a runtime created from an Asyncify build.
+   */
+  async executePendingJobsAsync(
+    maxJobsToExecute: number | void = -1,
+  ): Promise<ExecutePendingJobsResult> {
+    const ctxPtrOut = this.memory.newMutablePointerArray<JSContextPointerPointer>(1)
+    try {
+      const valuePtr = await this.ffi.QTS_ExecutePendingJob_MaybeAsync(
+        this.rt.value,
+        maxJobsToExecute ?? -1,
+        ctxPtrOut.value.ptr,
+      )
+      const ctxPtr = ctxPtrOut.value.typedArray[0] as JSContextPointer
+      return this.resolveExecutePendingJobsResult(valuePtr, ctxPtr)
+    } finally {
+      ctxPtrOut.dispose()
+    }
+  }
 }

packages/quickjs-emscripten-core/src/runtime.ts

@@ -3,6 +3,7 @@ import type {
   JSContextPointer,
   JSContextPointerPointer,
   JSRuntimePointer,
+  JSValuePointer,
   EitherFFI,
   EitherModule,
 } from "@jitl/quickjs-ffi-types"
@@ -253,6 +254,14 @@ export class QuickJSRuntime extends UsingDisposable implements Disposable {
 
     const ctxPtr = ctxPtrOut.value.typedArray[0] as JSContextPointer
     ctxPtrOut.dispose()
+    return this.resolveExecutePendingJobsResult(valuePtr, ctxPtr)
+  }
+
+  /** @private */
+  protected resolveExecutePendingJobsResult(
+    valuePtr: JSValuePointer,
+    ctxPtr: JSContextPointer,
+  ): ExecutePendingJobsResult {
     if (ctxPtr === 0) {
       // No jobs executed.
       this.ffi.QTS_FreeValuePointerRuntime(this.rt.value, valuePtr)

packages/quickjs-emscripten/src/quickjs.test.ts

@@ -1224,6 +1224,34 @@ function asyncContextTests(
   })
 
   describe("asyncify functions", () => {
+    it("supports sequential awaited host calls in one evaluation", async () => {
+      let asyncFunctionCalls = 0
+      vm.newAsyncifiedFunction("get", async (pathHandle) => {
+        asyncFunctionCalls++
+        const path = vm.getString(pathHandle)
+        return vm.newString(JSON.stringify({ path }))
+      }).consume((fn) => vm.setProp(vm.global, "get", fn))
+
+      const result = await vm.evalCodeAsync(`
+        (async () => {
+          const a = JSON.parse(await get("/a"))
+          const b = JSON.parse(await get("/b"))
+          const c = JSON.parse(await get("/c"))
+          return [a, b, c]
+        })()
+      `)
+
+      const promise = vm.unwrapResult(result).consume((handle) => vm.resolvePromise(handle))
+      vm.unwrapResult(await vm.runtime.executePendingJobsAsync())
+      const resolved = vm.unwrapResult(await promise)
+      assert.deepEqual(vm.dump(resolved), [{ path: "/a" }, { path: "/b" }, { path: "/c" }])
+      resolved.dispose()
+      assert.equal(asyncFunctionCalls, 3)
+
+      const reuseResult = await vm.evalCodeAsync("1 + 1")
+      assert.equal(vm.unwrapResult(reuseResult).consume(vm.dump), 2)
+    })
+
     it("sees Promise<handle> as synchronous", async () => {
       let asyncFunctionCalls = 0
       const asyncFn = async () => {

scripts/generate.ts

@@ -223,21 +223,15 @@ function renderFunction(args: {
 
   const ffiParams = JSON.stringify(params.map((param) => param.type.ffi))
   const cwrapArgs = [JSON.stringify(functionName), JSON.stringify(returnType.ffi), ffiParams]
-  if (context.DEBUG && async) {
+  if (async) {
     // https://emscripten.org/docs/porting/asyncify.html#usage-with-ccall
     // Passing {async:true} to cwrap/ccall will wrap all return values in
     // Promise.resolve(...), even if the c code doesn't suspend and returns a
     // primitive value.
     //
-    // When compiled with -s ASSERTIONS=1, Emscripten will throw if the
-    // function suspends and {async: true} wasn't passed.
-    //
-    // However, we'd like to avoid Promise/async overhead if the call can
-    // return a primitive value directly. So, we compile in {async:true}
-    // only in DEBUG mode, where assertions are enabled.
-    //
-    // Then we rely on our type system to ensure our code supports both
-    // primitive and promise-wrapped return values in production mode.
+    // Asyncify requires this option whenever the function may suspend. Debug
+    // builds assert when it is missing; release builds otherwise continue in
+    // a corrupted state.
     cwrapArgs.push("{ async: true }")
   }