Java JNI with QT application - Why it's use so many CPU resources?

ArtUrlWWW

I have Java JNI app with QT application.

Java class:
@
package my.site.processors.files.jni;

import java.io.File;

/**

@author ArtUrlWWW
*/
public class FfmpegStarter {

public native void run(String pathToFfmpegExe, String paramsArr[]);

}
@

QT code is:

@
#include "ffmpegstarterjni.h"
#include "mainwindow.h"
#include <QApplication>
#include <QStringList>

FfmpegStarterJNI::FfmpegStarterJNI()
{
}

JNIEXPORT void JNICALL Java_my_site_processors_files_jni_FfmpegStarter_run
(JNIEnv *env, jobject object, jstring pathToFfmpegExe, jobjectArray stringArray) {

int argc=0;
char *argv[1];

QApplication a(argc, argv);

a.exec&#40;&#41;;

}
@
With this code Java JVM used 100% of one core (25% from 4-core CPU).

If I comment a.exec(); code, then JVM doesn't use 100% of one CPU's core.

As I understand, this caused by a.exec(); (http://qt-project.org/doc/qt-5/qapplication.html#exec) - it makes loop, what can be ended by the QApplication::quit(); .

How to prevent huge CPU usage in JNI applications, which used QT and QApplication's function a.exec(); ?