CODEWITHSUNDEEP
javajava-native-interface
Green 绿色
Green 绿色

Reputation: 2916

Fill ArrayList in JNI yields Segfault

I made a very simple JNI application to fill an array. The C++ code should simply insert elements into the list. However, env->CallBooleanMethod yields a segmentation fault. The input arguments to this method are all not null. As far as I understand, this should work. What's the problem of this?

public class Main {
    public static void main(String[] args) {
        System.load("/path/to/project/Main.so");
        List<Integer> list = new ArrayList<>();
        Main.fill(list, 1);
        System.out.println(list);
    }

    private static native void fill(List<Integer> list, int n);
}

JNIEXPORT void JNICALL Java_Main_fill
    (JNIEnv *env, jclass cls, jobject jList, jint jn) {
  jclass jListCls = env->GetObjectClass(jList);
  jmethodID jListAddMethod = env->GetMethodID(jListCls, "add", "(Ljava/lang/Object;)Z");
  for (int i = 0; i < jn; i++) {
    env->CallBooleanMethod(jList, jListAddMethod, (jint) i); // <- Segfault occurs here
  }
  env->DeleteLocalRef(jListCls);
}

Upvotes: 1

Views: 66

Answers (1)

Michael
Michael

Reputation: 58467

Your list elements are of the type java.lang.Integer. In JNI code there's no autoboxing, so primitive integers won't get automatically converted to java.lang.Integer.

You'll have to get/create the java.lang.Integer instances yourself. That is, get a reference to that class using FindClass, get a reference to the static valueOf method, and then invoke it.

Upvotes: 2

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