Memory leak in SWIG polymorphism across C++ and Java using directors

Question

I have a C++ program to receive binary data from network. After data is received, it will callback the data as a byte array from C++ to a Java client. I use the director feature in SWIG to easily achieve cross language polymorphism across C++ and Java for callback. Here's a link .

But I found there is no typemaps in SWIG from char* in C++ to byte[] in Java. So, I added a patch to the virous.i. Here's a link .

/*Director specific typemaps*/
%typemap(directorin, descriptor="[B") char *BYTE {
    jbyteArray jb = (jenv)->NewByteArray(strlen(BYTE));
   (jenv)->SetByteArrayRegion(jb, 0, strlen(BYTE), (jbyte*)BYTE);
    $input = jb;
}
%typemap(directorout) char *BYTE {
$1 = 0;
if($input){
        $result = (char *) jenv->GetByteArrayElements($input, 0); 
        if(!$1) 
            return $null;
        jenv->ReleaseByteArrayElements($input, $result, 0);
    }
}
%typemap(javadirectorin) char *BYTE "$jniinput"
%typemap(javadirectorout) char *BYTE "$javacall"

For example. I have a class in C++ called A:

class A{
public:
       virtual void onDataReceived(const char* BYTE, const size_t len) {}
};

Then in Java code I have another class B to extend A:

class B extends A {
    @Override
    public void onDataReceived(byte[] data, long len) {
       //handling the data.
    }
}

I can receive the byte array in Java code, but it seems it is never garbage collected by JVM. The onDataReceived method in SWIG generated wrapper file is like this:

void SwigDirector_A::onDataReceived(char const *BYTE, size_t const len) {
  JNIEnvWrapper swigjnienv(this);
  JNIEnv * jenv = swigjnienv.getJNIEnv();
  jobject swigjobj = (jobject) NULL;
  jbyteArray jBYTE = 0;
  jlong jlen;

  if (!swig_override[3]) {
    A::onDataReceived(BYTE,len);
    return;
  }
  swigjobj = swig_get_self(jenv);
  if (swigjobj && jenv->IsSameObject(swigjobj, NULL) == JNI_FALSE) {
    {
      jbyteArray jb = (jenv)->NewByteArray(strlen(BYTE));
      (jenv)->SetByteArrayRegion(jb, 0, strlen(BYTE), (jbyte*)BYTE);
      jBYTE = jb;
    }
    jlen = (jlong) len;
    jenv->CallStaticVoidMethod(Swig::jclass_DataTransferJNI, Swig::director_methids[3], swigjobj, jBYTE, jlen);
    if (jenv->ExceptionCheck() == JNI_TRUE) return;
  } else {
    SWIG_JavaThrowException(jenv, SWIG_JavaNullPointerException, "null upcall object");
  }
  if (swigjobj) jenv->DeleteLocalRef(swigjobj);
}

In my C++ code, I will delete the data in the receive buffer after the callback is done. But I checked from Java VisualVM that the memory used by java client process is not GC-ed after a long time. Thanks advance for any help!

PS. The data is quite large, it is around 32KB.

Answer 1

I got it solved by added deletion of reference to jb in Director typemaps: (jenv)->DeleteLocalRef(jb);

Here's the updated patch .