无效的JNI引用(从c++调用Java方法)

Invalid JNI reference (calling Java method from c++)

本文关键字：调用 Java 方法 c++ JNI 引用 无效      更新时间：2023-10-16

我有一个问题，从c++调用启用GPS定位。我用SWIG生成了JNI包装器。日志提示:

01-02 17:14:03.816: D/dalvikvm(6165): Trying to load lib /data/data/com.example.swig/lib/libcppinterface.so 0x44e7ebf0
01-02 17:14:03.976: D/dalvikvm(6165): Added shared lib /data/data/com.example.swig/lib/libcppinterface.so 0x44e7ebf0
01-02 17:14:04.886: W/dalvikvm(6165): JNI WARNING: 0x44e8bb48 is not a valid JNI reference
01-02 17:14:04.886: W/dalvikvm(6165):              in Lcom/example/swig/cpplib/cppinterfaceJNI;.LocationSpotter_refresh (JLcom/example/swig/cpplib/LocationSpotter;)V (CallVoidMethodV)
01-02 17:14:04.886: I/dalvikvm(6165): "main" prio=5 tid=1 RUNNABLE
01-02 17:14:04.886: I/dalvikvm(6165):   | group="main" sCount=0 dsCount=0 s=N obj=0x4001d8e0 self=0xccb0
01-02 17:14:04.886: I/dalvikvm(6165):   | sysTid=6165 nice=0 sched=0/0 cgrp=default handle=-1345026008
01-02 17:14:04.886: I/dalvikvm(6165):   | schedstat=( 226108400 549900071 66 )
01-02 17:14:04.886: I/dalvikvm(6165):   at com.example.swig.cpplib.cppinterfaceJNI.LocationSpotter_refresh(Native Method)
01-02 17:14:04.896: I/dalvikvm(6165):   at com.example.swig.cpplib.LocationSpotter.refresh(LocationSpotter.java:56)
01-02 17:14:04.896: I/dalvikvm(6165):   at com.example.swig.MainActivity.onCreate(MainActivity.java:50)
01-02 17:14:04.896: I/dalvikvm(6165):   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-02 17:14:04.896: I/dalvikvm(6165):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
01-02 17:14:04.896: I/dalvikvm(6165):   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
01-02 17:14:04.896: I/dalvikvm(6165):   at android.app.ActivityThread.access$2300(ActivityThread.java:125)
01-02 17:14:04.896: I/dalvikvm(6165):   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
01-02 17:14:04.896: I/dalvikvm(6165):   at android.os.Handler.dispatchMessage(Handler.java:99)
01-02 17:14:04.896: I/dalvikvm(6165):   at android.os.Looper.loop(Looper.java:123)
01-02 17:14:04.896: I/dalvikvm(6165):   at android.app.ActivityThread.main(ActivityThread.java:4627)
01-02 17:14:04.896: I/dalvikvm(6165):   at java.lang.reflect.Method.invokeNative(Native Method)
01-02 17:14:04.896: I/dalvikvm(6165):   at java.lang.reflect.Method.invoke(Method.java:521)
01-02 17:14:04.896: I/dalvikvm(6165):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
01-02 17:14:04.896: I/dalvikvm(6165):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
01-02 17:14:04.896: I/dalvikvm(6165):   at dalvik.system.NativeStart.main(Native Method)
01-02 17:14:04.906: E/dalvikvm(6165): VM aborting
我用这一行从Java触发调用: 
LocationSpotter.getLocationSpotter().refresh();

getLocationSpotter()在c++中触发创建job对象(jSpotter)的代码:

// Retrieve the current JNIEnv* with the cached JVM
JNIEnv* env;
AndroidLocationSpotter::cachedJVM->AttachCurrentThread(&env, NULL);
jclass clazz = env->FindClass("com/example/swig/AndroidLocationSpotter");
jmethodID construct = env->GetMethodID(clazz, "<init>", "()V");
jSpotter = env->NewObject(clazz, construct);

和方法refresh()之后触发以下代码，导致应用程序崩溃:

// Retrieve the current JNIEnv* with the cached JVM
JNIEnv* env;
AndroidLocationSpotter::cachedJVM->AttachCurrentThread(&env, NULL);
jclass clazz = env->FindClass("com/example/swig/AndroidLocationSpotter");
jmethodID refresh = env->GetMethodID(clazz, "refresh", "()V");
env->CallVoidMethod(jSpotter, refresh); // The line where the crash happens

我还需要提到我在JNI_OnLoad函数中启动"cachedJVM"。希望有人能帮助我，谢谢。

编辑

工作代码:

// Retrieve the current JNIEnv* with the cached JVM
JNIEnv* env;
AndroidLocationSpotter::cachedJVM->AttachCurrentThread(&env, NULL);
jclass clazz = env->FindClass("com/example/swig/AndroidLocationSpotter");
jmethodID construct = env->GetMethodID(clazz, "<init>", "()V");
jSpotter = env->NewObject(clazz, construct);
jSpotter = env->NewGlobalRef(jSpotter);

您需要使用返回的jSpotter引用创建一个新的全局引用。当前使用的引用是当前帧的本地引用，并且将超出作用域(可能在DetachCurrentThread()时)。

您需要调用env->NewGlobalRef(jSpotter)或env->NewWeakGlobalRef(jSpotter)(两者都有相应的free函数)并使用返回的引用。

编辑

下面是一个正确的附加/分离处理的例子(假设您不需要线程进行进一步的Java操作): 
  JNIEnv* env;
  JavaVM* jvm = AndroidLocationSpotter::cachedJVM;
  int attached = jvm->GetEnv((void *)&env, JNI_VERSION_1_4) == JNI_OK;
  if (!attached) {
    if (jvm->AttachCurrentThread((void *)&env, NULL) != JNI_OK) {
      // Attach failed, handle error condition
      return;
    }
  }
  // Pushing a frame ensures proper cleanup of any local references you might generate
  // in your JNI code, e.g. with NewLocalRef (optional)                                                                                                                                                                                
  if (env->PushLocalFrame(16) < 0) {
    // Handle failed frame push error
  }
  else {
    // example local reference generation: ref2 = env->NewLocalRef(ref);
    //
    // Perform your primary Java operations here
    //
    env->PopLocalFrame(NULL);
  }
  if (!attached) {
    jvm->DetachCurrentThread();
  }
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