[Solved] How to pass by reference a QAndroidJniEnvironment object to a Qthread?

a.toraby

I have a thread object that works In the qt main thread I successfully can run this:

jbyteArray jBuffer = _env->NewByteArray(bufferSize);

The _env is a QAndroidJniEnvironment. but If I try to use _env in the run function of a Runnable, the application crashes and this error occurs:

Fatal signal 11 (SIGSEGV), code 1

This is the code:

class HelloWorldTask : public QRunnable
{
QAndroidJniEnvironment * _env;
void run()
{
    qDebug() << "Hello world from thread" << QThread::currentThread();
    jbyteArray jBuffer = (*_env)->NewByteArray(10);
    qDebug() << "Hello 2 world from thread" << QThread::currentThread();
}
public:
void setPointer(QAndroidJniEnvironment * p){
    _env = p;
}
};

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
HelloWorldTask * hello = new HelloWorldTask();
QAndroidJniEnvironment env;
QAndroidJniEnvironment * p = & env;
hello->setPointer(p);
QThreadPool::globalInstance()->start(hello);
return a.exec();
}

Could you please tell me how can I use the pointer to the QAndroidJniEnvironment or QAndroidJniObject in a new Qthread? so the application ui remains responsive during the execution of java process.

sneubert

To use an jni environment pointer by a different thread you have to call AttachCurrentThread.

a.toraby

@sneubert
Thanks for your reply. I tried he following code but I got fatal signal again!

JavaVM * _jvm = 0;
JNIEnv* _jniENV;
qDebug() << "Attaching current thread";
_jvm->AttachCurrentThread(&_jniENV,NULL);

Here is full error description:

D/Qt      (14352): ..\untitled4\main.cpp:47 (int main(int, char**)): Attaching current thread
F/libc    (14352): Fatal signal 11 (SIGSEGV), code 1, fault addr 0x0 in tid 14508 (QtThread)

jalomic

@a.toraby
_jvm and _jniENV are initialised ?

sneubert

_jniENV is a pointer already so try to pass it without & to AttachCurrentThread

jalomic

@a.toraby said:

JavaVM * _jvm = 0;
JNIEnv* _jniENV;
qDebug() << "Attaching current thread";
_jvm->AttachCurrentThread(&_jniENV,NULL);

As i see here _jvm - is a null pointer.. and you call method from null pointer

a.toraby

@jalomic said:

@a.toraby said:

JavaVM * _jvm = 0;
JNIEnv* _jniENV;
qDebug() << "Attaching current thread";
_jvm->AttachCurrentThread(&_jniENV,NULL);

As i see here _jvm - is a null pointer.. and you call method from null pointer

Yes you are right. I solved it by using a QAndroidJniEnvironment: Here is the working code:

class HelloWorldTask : public QRunnable
{
QAndroidJniEnvironment * _env;
void run()
{
    JNIEnv * jniEnv;
    JavaVM * jvm = _env->javaVM();
    qDebug() << "Getting jni environment";
    jvm->GetEnv(reinterpret_cast<void**>(&_env), JNI_VERSION_1_6);
    qDebug() << "Attaching current thread";
    jvm->AttachCurrentThread(&jniEnv,NULL);
    qDebug() << "Creating byte array" ;
    jbyteArray jBuffer = jniEnv->NewByteArray(10);
    qDebug() << "byte array created" ;
    jvm->DetachCurrentThread();
}
public:
void setPointer(QAndroidJniEnvironment * p){
    _env = p;
}
};

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();


HelloWorldTask * hello = new HelloWorldTask();


QAndroidJniEnvironment * env;
hello->setPointer(env);
// QThreadPool takes ownership and deletes 'hello' automatically
QThreadPool::globalInstance()->start(hello);
return a.exec();
}