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I'm using OpenCV with MXJ but I encounters an annoying problem. Let me explains

which contains a build folder which contains 

folder contains the native library of OpenCV and the JNI Jar I need to add to my Eclipse project 

image.png

 Then I create a Eclipse project, in the properties of this project I set up my Buildpath to use the OpenCV JNI and all an mxj externals needs :

 The OpenCV Native Library dll is placed in one of my PATH folder, "c:\windows\system32" in my case

by the way, I use the 1.7 JRE and it seems to work properly like that : 

public class TestOpenCV extends MaxObject {

static { System.loadLibrary(Core.NATIVE_LIBRARY_NAME); }

declareOutlets(new int[]{DataTypes.ALL}); 

Mat m = new Mat(5, 9, CvType.CV_8UC4, new Scalar(0));

OpenCV seems correctly implemented, for exemple, I can instantiate a Mat object and post its content to Max console. 

Sending a bang I get the content of the Mat Object : 

0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0; 

1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 5, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0;

0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 

Problems appears when I change the Java code of the mxj object. To update my object, I delete it and recreate it again. Then, the errors appears in Max Console :

C:\Windows\System32\opencv_java300.dll already loaded in another

 at java.lang.ClassLoader.loadLibrary1(Unknown Source) at java.lang.ClassLoader.loadLibrary0(Unknown Source) at java.lang.ClassLoader.loadLibrary(Unknown Source) at java.lang.Runtime.loadLibrary0(Unknown Source) at java.lang.System.loadLibrary(Unknown Source) at OpenCVClassLoad.loadNativeLibrary(OpenCVClassLoad.java:5) at TestOpenCV.(TestOpenCV.java:22) (mxj) unable to alloc instance of TestOpenCV 

https://cycling74.com/articles/mxj-class-loading

 , It's clear that when I create a new MXJ with a more recent class file, a new class loader is used, but the Native Library stills loaded and that's what generate this errors. Unfortunatly, that article don't seems to provide any solutions.

Only things I can do then is close and restart Max/MSP.

I found a lot of questions about this kind of problem on Stack Overflow but nothing helped, most of the time it concerns something called Tomcat that I never used.

Use a custom class loader ? That's a solution 

 but it seems hard to implement. With this solution, I could maybe unload the Native Library inside a notifyDelete() method. 

Re-use the Native Library already loaded ? Don't know if it's possible..

 Doing some research on Github, hoping to find an example using Native Library I find this one : 

 (the only one) He don't use "System.loadLibrary" so he has an alternative method, I notice he recommend to place the DLL in 

 resources\packages\max-mxj\java-classes\lib 

A magical stuff to do in notifyDelete() ?

Someone tell me it was possible to solve this by setting "Native Library Location" in build path's Eclipse project but it doesn't helped, maybe I'm doing it wrong ?

Place the DLL in '.../Max 7/resources/support' ?

I don't know what to do against this and that's really annoying because I'm really near to have the complete solution to use OpenCV properly with mxj :'(

(Windows 7 , Max 7 64 bit)
1. I downloaded the  OpenCV archive, this is a 7-zip self extractor.
2. I obtain a folder called opencv which contains a build folder which contains  java.
3. This java folder contains the native library of OpenCV and the JNI Jar I need to add to my Eclipse project 



4. Then I create a Eclipse project, in the properties of this project I  set up my Buildpath to use the OpenCV JNI and all an mxj externals needs :


5. The OpenCV Native Library dll is placed in one of my PATH folder,  "c:\windows\system32" in my case

by the way, I use the 1.7 JRE and it seems to work properly like that : 


( Highlighted syntax version on PasteBin  ) 


import com.cycling74.max.*;
import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.core.Scalar;

public class TestOpenCV extends MaxObject {
  static { System.loadLibrary(Core.NATIVE_LIBRARY_NAME); }
  
  public TestOpenCV(Atom[] args)
  {
    declareInlets(new int[]{DataTypes.ALL});
    declareOutlets(new int[]{DataTypes.ALL});  
  }
  
  public void bang() { 
    Mat m = new Mat(5, 9, CvType.CV_8UC4, new Scalar(0));
    Mat mr1 = m.row(1);
    mr1.setTo(new Scalar(1));
    Mat mc5 = m.col(3);
    mc5.setTo(new Scalar(5));
    post("OpenCV Mat data:\n" + m.dump()); 
  }
}

 OpenCV seems correctly implemented, for exemple, I can instantiate a Mat object and post its content to Max console. 

 Sending a bang I get the content of the Mat Object :  

OpenCV Mat data: [
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0;  
1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 5, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0;
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
... And so on

 Problems appears when I change the Java code of the mxj object. To update my object, I delete it and recreate it again.  Then, the errors appears in Max Console : 

 java.lang.UnsatisfiedLinkError: Native Library C:\Windows\System32\opencv_java300.dll already loaded in another classloader at java.lang.ClassLoader.loadLibrary1(Unknown Source) at java.lang.ClassLoader.loadLibrary0(Unknown Source) at java.lang.ClassLoader.loadLibrary(Unknown Source) at java.lang.Runtime.loadLibrary0(Unknown Source) at java.lang.System.loadLibrary(Unknown Source) at OpenCVClassLoad.loadNativeLibrary(OpenCVClassLoad.java:5) at TestOpenCV.(TestOpenCV.java:22) (mxj) unable to alloc instance of TestOpenCV 

 Reading this article : https://cycling74.com/articles/mxj-class-loading , It's clear that when I create a new MXJ with a more recent class file, a new class loader is used, but the Native Library stills loaded and that's what generate this errors.  Unfortunatly, that article don't seems to provide any solutions.  

Only things I can do then is close and restart Max/MSP.


1. Use a custom  class loader ?  That's a solution I read here  but it seems hard to implement. With this solution, I could maybe unload the Native Library inside a notifyDelete() method. 
 
2. Re-use the Native Library already loaded ? Don't know if it's possible..

3. Doing some research on Github, hoping to find an example using Native Library I find this one : https://github.com/timini/maxSerial (the only one) He don't use "System.loadLibrary" so he has an alternative method, I notice he recommend to place the DLL in java/lib (Max5),  probably  resources\packages\max-mxj\java-classes\lib Today. Could it be the solution ? 

4. A magical stuff to do in  notifyDelete() ?  

5. Someone tell me it was possible to solve this by setting "Native Library Location" in build path's  Eclipse project but it doesn't helped, maybe I'm doing it wrong ? 

6. Place the DLL in '.../Max 7/resources/support' ? 

 I don't know what to do against this and that's really annoying because I'm really near to have the complete solution to use OpenCV properly with mxj :'(  

I'm using OpenCV with MXJ but I encounters an annoying problem. Let me explains
Instructions for OpenCV with mxj
(Windows 7 , Max 7 64 bit)


mxj-class-loader-problem-with-opencv-native-library

Please verify your library path is right or not. Of course, you can use following code to check your library 

System.out.println(System.getProperty("java.library.path"));

Please verify your library path is right or not. Of course, you can use following code to check your library path : System.out.println(System.getProperty("java.library.path"));

You can appoint the java.library.path when launching a Java application:

MXJ Class Loader problem with OpenCV Native Library