fix: eliminate race in GetParcelableExtra, simplify HandlerThread.Close

- GetParcelableExtra: use sync.Once for thread-safe lazy method ID init
  instead of bare nil check (concurrent vm.Do calls could race)
- HandlerThread.Close: remove redundant ensureInit (QuitSafely already
  calls it), avoid nested vm.Do by calling QuitSafely before DeleteGlobalRef

Author: xaionaro@dx.center

app/intent_parcelable_extra.go

@@ -2,13 +2,17 @@ package app
 
 import (
 	"fmt"
+	"sync"
 	"unsafe"
 
 	"github.com/AndroidGoLab/jni"
 )
 
-// midIntentGetParcelableExtra is lazily initialized on first call.
-var midIntentGetParcelableExtra jni.MethodID
+var (
+	parcelableExtraOnce sync.Once
+	parcelableExtraMid  jni.MethodID
+	parcelableExtraErr  error
+)
 
 // GetParcelableExtra calls android.content.Intent.getParcelableExtra(String).
 // This method is deprecated in API 33 but remains the standard way to extract
@@ -23,17 +27,16 @@ func (m *Intent) GetParcelableExtra(
 			return err
 		}
 
-		if midIntentGetParcelableExtra == nil {
-			mid, err := env.GetMethodID(
+		parcelableExtraOnce.Do(func() {
+			parcelableExtraMid, parcelableExtraErr = env.GetMethodID(
 				(*jni.Class)(unsafe.Pointer(clsIntent)),
 				"getParcelableExtra",
 				"(Ljava/lang/String;)Landroid/os/Parcelable;",
 			)
-			if err != nil {
-				callErr = fmt.Errorf("android.content.Intent.getParcelableExtra is not available on this device")
-				return callErr
-			}
-			midIntentGetParcelableExtra = mid
+		})
+		if parcelableExtraErr != nil {
+			callErr = fmt.Errorf("android.content.Intent.getParcelableExtra is not available on this device")
+			return callErr
 		}
 
 		jKey, err := env.NewStringUTF(key)
@@ -44,7 +47,7 @@ func (m *Intent) GetParcelableExtra(
 
 		result, callErr = env.CallObjectMethod(
 			m.Obj,
-			midIntentGetParcelableExtra, jni.ObjectValue(&jKey.Object),
+			parcelableExtraMid, jni.ObjectValue(&jKey.Object),
 		)
 		if callErr != nil {
 			return callErr

os/new_handler_thread.go

@@ -61,17 +61,14 @@ func NewHandlerThread(
 
 // Close quits the thread safely and releases the global reference.
 func (m *HandlerThread) Close() {
-	if m.Obj != nil {
-		_ = m.VM.Do(func(env *jni.Env) error {
-			if err := ensureInit(env); err != nil {
-				return err
-			}
-			if midHandlerThreadQuitSafely != nil {
-				_, _ = m.QuitSafely()
-			}
-			env.DeleteGlobalRef(m.Obj)
-			m.Obj = nil
-			return nil
-		})
+	if m.Obj == nil {
+		return
 	}
+	// QuitSafely calls ensureInit and vm.Do internally.
+	_, _ = m.QuitSafely()
+	_ = m.VM.Do(func(env *jni.Env) error {
+		env.DeleteGlobalRef(m.Obj)
+		m.Obj = nil
+		return nil
+	})
 }