perf(ioscompanion): count read spans toward settle and capture snapshots concurrently

internal/driver/ioscompanion/driver.go

@@ -741,17 +741,27 @@ func (d *Driver) Screenshot(ctx context.Context) (driver.Image, error) {
 func (d *Driver) Snapshot(ctx context.Context) (string, driver.Image, error) {
 	d.mu.Lock()
 	defer d.mu.Unlock()
+
+	// The hierarchy and the screenshot ride different transports on the
+	// hybrid path, so they are captured concurrently. Only the hierarchy leg
+	// runs under withRecovery: two concurrent recoveries would race the
+	// restart bookkeeping, and a screenshot connection failure surfaces as a
+	// plain error that the next serialized call recovers from.
+	var data []byte
+	screenshotDone := make(chan error, 1)
+	go func() {
+		imageData, _, callErr := d.companion.Screenshot(ctx)
+		data = imageData
+		screenshotDone <- callErr
+	}()
+
 	dump, err := d.describeAll(ctx)
+	screenshotErr := <-screenshotDone
 	if err != nil {
 		return "", driver.Image{}, err
 	}
-	var data []byte
-	if err := d.withRecovery(ctx, func() error {
-		var screenshotErr error
-		data, _, screenshotErr = d.companion.Screenshot(ctx)
-		return screenshotErr
-	}); err != nil {
-		return "", driver.Image{}, fmt.Errorf("screenshot: %w", err)
+	if screenshotErr != nil {
+		return "", driver.Image{}, fmt.Errorf("screenshot: %w", screenshotErr)
 	}
 	mapped, err := MapHierarchy(dump, d.screenWidth, d.screenHeight)
 	if err != nil {

internal/driver/ioscompanion/driver_test.go

@@ -13,6 +13,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -27,7 +28,10 @@ import (
 // the order of calls and returns scripted results, so the driver's decision
 // logic is testable without a live simulator.
 type fakeCompanion struct {
-	calls []string
+	// callsMutex guards calls: Snapshot captures the hierarchy and the
+	// screenshot concurrently.
+	callsMutex sync.Mutex
+	calls      []string
 
 	accessibilityJSON string
 	accessibilityErr  error
@@ -40,7 +44,19 @@ type fakeCompanion struct {
 	hidErr error
 }
 
-func (f *fakeCompanion) record(name string) { f.calls = append(f.calls, name) }
+func (f *fakeCompanion) record(name string) {
+	f.callsMutex.Lock()
+	defer f.callsMutex.Unlock()
+	f.calls = append(f.calls, name)
+}
+
+func (f *fakeCompanion) recorded() []string {
+	f.callsMutex.Lock()
+	defer f.callsMutex.Unlock()
+	out := make([]string, len(f.calls))
+	copy(out, f.calls)
+	return out
+}
 
 func (f *fakeCompanion) AccessibilityInfo(context.Context) (string, error) {
 	f.record("accessibility")
@@ -218,7 +234,7 @@ func TestLaunchRejectsEnvironment(t *testing.T) {
 	}
 }
 
-func TestSnapshotPairsHierarchyThenScreenshot(t *testing.T) {
+func TestSnapshotPairsHierarchyAndScreenshot(t *testing.T) {
 	companion := &fakeCompanion{
 		accessibilityJSON: "[]",
 		screenshotData:    samplePNG(t, 390, 844),
@@ -231,8 +247,11 @@ func TestSnapshotPairsHierarchyThenScreenshot(t *testing.T) {
 	if image.Width != 390 || image.Height != 844 {
 		t.Fatalf("image dims = %dx%d, want 390x844", image.Width, image.Height)
 	}
-	if indexOf(companion.calls, "accessibility") > indexOf(companion.calls, "screenshot") {
-		t.Fatalf("accessibility must precede screenshot; got %v", companion.calls)
+	// The two captures run concurrently (they ride different transports on
+	// the hybrid path), so both must happen but in no particular order.
+	calls := companion.recorded()
+	if indexOf(calls, "accessibility") < 0 || indexOf(calls, "screenshot") < 0 {
+		t.Fatalf("snapshot must capture hierarchy and screenshot; got %v", calls)
 	}
 }
 

internal/driver/ioscompanion/settle.go

@@ -56,33 +56,30 @@ func SystemClock() Clock { return systemClock{} }
 // capped at StabilityPollCap. fetch returns the current hierarchy tree (nil on
 // fetch failure, treated like a transitional snapshot so the streak resets).
 //
-// The loop mirrors the companion's JVM implementation: it samples a prior
-// snapshot, then on each tick sleeps the poll interval, fetches a fresh
-// snapshot, and grows the streak only while consecutive snapshots are both
-// non-transitional and structurally identical. A transitional snapshot, a
-// changed snapshot, or a fetch failure resets the streak. The function returns
-// when the streak reaches MinStableStreak or the cap elapses, and respects
-// context cancellation.
+// The stable stretch is measured from the start of the earliest read in the
+// current run of identical snapshots: a fetch is not instantaneous (a runner
+// snapshot takes a fair fraction of the streak itself), and the UI changing
+// mid-read would change the snapshot, so the read's own duration is evidence
+// of stability. A transitional snapshot, a changed snapshot, or a fetch
+// failure resets the run. The function returns when the stretch reaches
+// MinStableStreak or the cap elapses, and respects context cancellation.
 func PollUntilStable(ctx context.Context, clock Clock, fetch func() *hierarchy.Tree) {
 	deadline := clock.Now().Add(StabilityPollCap)
+	runStart := clock.Now()
 	prior := snapshot(fetch)
-	var streakStart time.Time
 	for clock.Now().Before(deadline) {
 		if ctx.Err() != nil {
 			return
 		}
 		clock.Sleep(StabilityPollInterval)
+		currentStart := clock.Now()
 		current := snapshot(fetch)
-		now := clock.Now()
 		if prior.valid && current.valid && prior.hash == current.hash {
-			if streakStart.IsZero() {
-				streakStart = now
-			}
-			if now.Sub(streakStart) >= MinStableStreak {
+			if clock.Now().Sub(runStart) >= MinStableStreak {
 				return
 			}
 		} else {
-			streakStart = time.Time{}
+			runStart = currentStart
 		}
 		prior = current
 	}