Fix Await to process Go-scheduled jobs instead of blocking in js_std_loop (#690)

* fix: replace blocking js_std_loop in Await with cooperative polling

* fix: feedback from gemini

* fix: adding one more test

* fix: more coverage

- the nil check on ctx.jobQueue at line 1056 is redundant since len() on a nil channel returns 0
- more coverage

Author: davidroman0O

context.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"sync/atomic"
+	"time"
 	"unsafe"
 )
 
@@ -25,6 +26,11 @@ type Context struct {
 
 const defaultJobQueueSize = 1024
 
+// awaitPollInterval is the duration the Await loop sleeps when no JS or Go
+// jobs are pending. Keeps CPU usage low while ensuring Go-scheduled work
+// (e.g., resolved Promises from goroutines) is picked up promptly.
+const awaitPollInterval = time.Millisecond
+
 // awaitPromiseStateHook and awaitExecutePendingJobHook are used only in tests to
 // force specific Await code paths; they must remain nil in production.
 var (
@@ -985,7 +991,13 @@ func (ctx *Context) Loop() {
 	ctx.ProcessJobs()
 }
 
-// Wait for a promise and execute pending jobs while waiting for it. Return the promise result or JS_EXCEPTION in case of promise rejection.
+// Wait for a promise and execute pending jobs while waiting for it.
+// Return the promise result or JS_EXCEPTION in case of promise rejection.
+//
+// This implementation uses a polling loop instead of blocking in js_std_loop.
+// This allows Go-scheduled work (via ctx.Schedule) to be processed between
+// iterations, enabling async Go bridge functions (fetch, storage, etc.) to
+// resolve Promises from goroutines without blocking the event loop.
 func (ctx *Context) Await(v *Value) *Value {
 	if v == nil || !v.IsPromise() {
 		return v
@@ -1002,7 +1014,9 @@ func (ctx *Context) Await(v *Value) *Value {
 	runtimeRef := ctx.runtime.ref
 
 	for {
+		// Drain Go-scheduled work (resolve/reject from goroutines)
 		ctx.ProcessJobs()
+
 		state := C.JS_PromiseState(ctx.ref, promise.ref)
 		if hook := awaitPromiseStateHook; hook != nil {
 			if override, ok := hook(ctx, promise, int(state)); ok {
@@ -1016,6 +1030,7 @@ func (ctx *Context) Await(v *Value) *Value {
 			reason := C.JS_PromiseResult(ctx.ref, promise.ref)
 			return &Value{ctx: ctx, ref: C.JS_Throw(ctx.ref, reason)}
 		case pendingState:
+			// Process JS microtasks (Promise.then callbacks, queueMicrotask)
 			executed := C.JS_ExecutePendingJob(runtimeRef, nil)
 			if hook := awaitExecutePendingJobHook; hook != nil {
 				if override, ok := hook(ctx, promise, int(executed)); ok {
@@ -1026,7 +1041,22 @@ func (ctx *Context) Await(v *Value) *Value {
 				return ctx.ThrowInternalError("failed to execute pending job")
 			}
 			if executed == 0 {
-				C.js_std_loop(ctx.ref)
+				// No JS microtasks pending. Check for Go-scheduled work first.
+				ctx.ProcessJobs()
+
+				// Re-check promise state — Go jobs may have resolved it.
+				newState := C.JS_PromiseState(ctx.ref, promise.ref)
+				if newState != pendingState {
+					continue // resolved — loop back to handle it
+				}
+
+				// Still pending. Check if there are pending Go jobs in the queue.
+				// If so, keep polling. If not, yield briefly — a goroutine will
+				// Schedule work soon (HTTP response, storage result, etc.)
+				if len(ctx.jobQueue) > 0 {
+					continue // more Go jobs to process
+				}
+				time.Sleep(awaitPollInterval)
 			}
 		default:
 			return v

context_test.go

@@ -1002,17 +1002,52 @@ func TestContextInternalsCoverage(t *testing.T) {
 		require.Nil(t, ctx.Await(nilPromise))
 	})
 
-	t.Run("AwaitDrivesStdLoopForTimeout", func(t *testing.T) {
+	t.Run("AwaitDrivesScheduleForResolve", func(t *testing.T) {
 		rt := NewRuntime()
 		defer rt.Close()
 		ctx := rt.NewContext()
 		defer ctx.Close()
 
-		promise := ctx.Eval(`new Promise((resolve) => { setTimeout(() => resolve("timer result"), 0); })`)
+		// Test that Await processes Go-scheduled work (via ctx.Schedule)
+		// instead of relying on js_std_loop for C-level timers.
+		promise := ctx.NewPromise(func(resolve, reject func(*Value)) {
+			go func() {
+				ctx.Schedule(func(ctx *Context) {
+					val := ctx.NewString("scheduled result")
+					defer val.Free()
+					resolve(val)
+				})
+			}()
+		})
+		defer promise.Free()
+		result := ctx.Await(promise)
+		defer result.Free()
+		require.Equal(t, "scheduled result", result.ToString())
+	})
+
+	t.Run("AwaitPollsUntilDelayedResolve", func(t *testing.T) {
+		rt := NewRuntime()
+		defer rt.Close()
+		ctx := rt.NewContext()
+		defer ctx.Close()
+
+		// Test that the Await polling loop correctly yields and re-checks
+		// when the Promise is resolved after a delay from a goroutine.
+		// This exercises the time.Sleep path in Await's pending case.
+		promise := ctx.NewPromise(func(resolve, reject func(*Value)) {
+			go func() {
+				time.Sleep(5 * time.Millisecond) // force Await to poll a few times
+				ctx.Schedule(func(ctx *Context) {
+					val := ctx.NewString("delayed result")
+					defer val.Free()
+					resolve(val)
+				})
+			}()
+		})
 		defer promise.Free()
 		result := ctx.Await(promise)
 		defer result.Free()
-		require.Equal(t, "timer result", result.ToString())
+		require.Equal(t, "delayed result", result.ToString())
 	})
 
 	t.Run("AwaitHandlesPendingJobFailure", func(t *testing.T) {
@@ -1043,6 +1078,87 @@ func TestContextInternalsCoverage(t *testing.T) {
 		require.Contains(t, err.Error(), "failed to execute pending job")
 	})
 
+	// Cover line 1049-1050: executed==0, ProcessJobs resolves the promise,
+	// re-check sees non-pending state → continue.
+	t.Run("AwaitReCheckResolvesAfterProcessJobs", func(t *testing.T) {
+		rt := NewRuntime()
+		defer rt.Close()
+		ctx := rt.NewContext()
+		defer ctx.Close()
+
+		var resolvePromise func(*Value)
+		promise := ctx.NewPromise(func(resolve, reject func(*Value)) {
+			resolvePromise = resolve
+		})
+		defer promise.Free()
+
+		firstCall := true
+		awaitExecutePendingJobHook = func(hookCtx *Context, _ *Value, current int) (int, bool) {
+			if hookCtx != ctx {
+				return current, false
+			}
+			if firstCall {
+				firstCall = false
+				// Schedule a job that resolves the promise. ProcessJobs() at
+				// line 1045 will pick it up, so the re-check at line 1048
+				// sees fulfilled state.
+				ctx.Schedule(func(inner *Context) {
+					val := inner.NewString("resolved-via-recheck")
+					defer val.Free()
+					resolvePromise(val)
+				})
+				return 0, true // force executed=0
+			}
+			return current, false
+		}
+		t.Cleanup(func() { awaitExecutePendingJobHook = nil })
+
+		result := ctx.Await(promise)
+		defer result.Free()
+		require.Equal(t, "resolved-via-recheck", result.ToString())
+	})
+
+	// Cover line 1056-1057: executed==0, ProcessJobs drains but promise
+	// stays pending, yet another Go job is already queued → continue.
+	t.Run("AwaitContinuesWhenJobQueueNonEmpty", func(t *testing.T) {
+		rt := NewRuntime()
+		defer rt.Close()
+		ctx := rt.NewContext()
+		defer ctx.Close()
+
+		var resolvePromise func(*Value)
+		promise := ctx.NewPromise(func(resolve, reject func(*Value)) {
+			resolvePromise = resolve
+		})
+		defer promise.Free()
+
+		callCount := 0
+		awaitExecutePendingJobHook = func(hookCtx *Context, _ *Value, current int) (int, bool) {
+			if hookCtx != ctx {
+				return current, false
+			}
+			callCount++
+			if callCount == 1 {
+				// First iteration: force executed=0, and enqueue two jobs.
+				// ProcessJobs at line 1045 drains the first, but the second
+				// remains → len(jobQueue) > 0 → continue (line 1056-1057).
+				ctx.Schedule(func(*Context) {}) // drained by ProcessJobs
+				ctx.Schedule(func(inner *Context) { // stays in queue → triggers continue
+					val := inner.NewString("after-queue-check")
+					defer val.Free()
+					resolvePromise(val)
+				})
+				return 0, true
+			}
+			return current, false
+		}
+		t.Cleanup(func() { awaitExecutePendingJobHook = nil })
+
+		result := ctx.Await(promise)
+		defer result.Free()
+		require.Equal(t, "after-queue-check", result.ToString())
+	})
+
 	t.Run("AwaitFallsBackOnUnexpectedState", func(t *testing.T) {
 		rt := NewRuntime()
 		defer rt.Close()