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AttachCurrentThread Is Stuck in JNI

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0

I am trying to understand the strange behaviour of JNI Application. I am starting the thread from native JNI dll routine (sayHello), which in its turn when started, tries to attach to JVM thread to acquire the the environment variable. However it seams that it cannot do so unless main thread is exiting. How come? In example below (disregard the thread memory leak) the thread routine foo will succeed to attach to JVM only after Thread.sleep(5000) in main thread; Why is that?

OUTPUT:

Hello World!!!
Hello World from C++!
Hello FROM FOO
Good Bye World!!!

 %%% JNIEnv attached : 00000206FF8E7B40

JAVA CODE

package com.home;

public class Main 

 static 
 System.loadLibrary("JNITest"); // Load native library hello.dll (Windows) or libhello.so (Unixes)
 // at runtime
 // This library contains a native method called sayHello()
 

 public static void main(String[] args) throws Exception 
 // TODO Auto-generated method stub

 System.out.println("Hello World!!!");

 new Main().sayHello();

 Thread.sleep(5000);

 System.out.println("Good Bye World!!!");

 

 // Declare an instance native method sayHello() which receives no parameter and returns void
 private native void sayHello();

JNI DLL

// JNITest.cpp : Defines the exported functions for the DLL application.
//
#include "com_home_Main.h"
#include "stdafx.h"
#include <iostream>
#include <thread> 

static JavaVM *g_jVM = NULL;

using namespace std;
void foo()

 JNIEnv *jEnv = NULL;

 cout << "Hello FROM FOO" << endl;

 g_jVM->AttachCurrentThreadAsDaemon((void **)(&jEnv), NULL);
 if (jEnv == NULL)
 
 std::cout << "n !!! Failed to attach current thread with JVM !!! n";

 
 else
 
 std::cout << "n %%%t JNIEnv attached : " << (void *)jEnv;
 g_jVM->DetachCurrentThread();
 




extern "C"
// Implementation of the native method sayHello()
JNIEXPORT void JNICALL Java_com_home_Main_sayHello(JNIEnv *env, jobject thisObj) 
 cout << "Hello World from C++!" << endl;

 env->GetJavaVM(&g_jVM);

 std::thread *first = new std::thread(foo);

 return;

java multithreading java-native-interface

share|improve this question

edited Mar 25 at 1:32

Boris

asked Mar 25 at 1:20

BorisBoris

566628

add a comment | 

0

I am trying to understand the strange behaviour of JNI Application. I am starting the thread from native JNI dll routine (sayHello), which in its turn when started, tries to attach to JVM thread to acquire the the environment variable. However it seams that it cannot do so unless main thread is exiting. How come? In example below (disregard the thread memory leak) the thread routine foo will succeed to attach to JVM only after Thread.sleep(5000) in main thread; Why is that?

OUTPUT:

Hello World!!!
Hello World from C++!
Hello FROM FOO
Good Bye World!!!

 %%% JNIEnv attached : 00000206FF8E7B40

JAVA CODE

package com.home;

public class Main 

 static 
 System.loadLibrary("JNITest"); // Load native library hello.dll (Windows) or libhello.so (Unixes)
 // at runtime
 // This library contains a native method called sayHello()
 

 public static void main(String[] args) throws Exception 
 // TODO Auto-generated method stub

 System.out.println("Hello World!!!");

 new Main().sayHello();

 Thread.sleep(5000);

 System.out.println("Good Bye World!!!");

 

 // Declare an instance native method sayHello() which receives no parameter and returns void
 private native void sayHello();

JNI DLL

// JNITest.cpp : Defines the exported functions for the DLL application.
//
#include "com_home_Main.h"
#include "stdafx.h"
#include <iostream>
#include <thread> 

static JavaVM *g_jVM = NULL;

using namespace std;
void foo()

 JNIEnv *jEnv = NULL;

 cout << "Hello FROM FOO" << endl;

 g_jVM->AttachCurrentThreadAsDaemon((void **)(&jEnv), NULL);
 if (jEnv == NULL)
 
 std::cout << "n !!! Failed to attach current thread with JVM !!! n";

 
 else
 
 std::cout << "n %%%t JNIEnv attached : " << (void *)jEnv;
 g_jVM->DetachCurrentThread();
 




extern "C"
// Implementation of the native method sayHello()
JNIEXPORT void JNICALL Java_com_home_Main_sayHello(JNIEnv *env, jobject thisObj) 
 cout << "Hello World from C++!" << endl;

 env->GetJavaVM(&g_jVM);

 std::thread *first = new std::thread(foo);

 return;

java multithreading java-native-interface

share|improve this question

edited Mar 25 at 1:32

Boris

asked Mar 25 at 1:20

BorisBoris

566628

add a comment | 

I am trying to understand the strange behaviour of JNI Application. I am starting the thread from native JNI dll routine (sayHello), which in its turn when started, tries to attach to JVM thread to acquire the the environment variable. However it seams that it cannot do so unless main thread is exiting. How come? In example below (disregard the thread memory leak) the thread routine foo will succeed to attach to JVM only after Thread.sleep(5000) in main thread; Why is that?

OUTPUT:

Hello World!!!
Hello World from C++!
Hello FROM FOO
Good Bye World!!!

 %%% JNIEnv attached : 00000206FF8E7B40

JAVA CODE

package com.home;

public class Main 

 static 
 System.loadLibrary("JNITest"); // Load native library hello.dll (Windows) or libhello.so (Unixes)
 // at runtime
 // This library contains a native method called sayHello()
 

 public static void main(String[] args) throws Exception 
 // TODO Auto-generated method stub

 System.out.println("Hello World!!!");

 new Main().sayHello();

 Thread.sleep(5000);

 System.out.println("Good Bye World!!!");

 

 // Declare an instance native method sayHello() which receives no parameter and returns void
 private native void sayHello();

JNI DLL

// JNITest.cpp : Defines the exported functions for the DLL application.
//
#include "com_home_Main.h"
#include "stdafx.h"
#include <iostream>
#include <thread> 

static JavaVM *g_jVM = NULL;

using namespace std;
void foo()

 JNIEnv *jEnv = NULL;

 cout << "Hello FROM FOO" << endl;

 g_jVM->AttachCurrentThreadAsDaemon((void **)(&jEnv), NULL);
 if (jEnv == NULL)
 
 std::cout << "n !!! Failed to attach current thread with JVM !!! n";

 
 else
 
 std::cout << "n %%%t JNIEnv attached : " << (void *)jEnv;
 g_jVM->DetachCurrentThread();
 




extern "C"
// Implementation of the native method sayHello()
JNIEXPORT void JNICALL Java_com_home_Main_sayHello(JNIEnv *env, jobject thisObj) 
 cout << "Hello World from C++!" << endl;

 env->GetJavaVM(&g_jVM);

 std::thread *first = new std::thread(foo);

 return;

java multithreading java-native-interface

share|improve this question

edited Mar 25 at 1:32

Boris

asked Mar 25 at 1:20

BorisBoris

566628

Hello World!!!
Hello World from C++!
Hello FROM FOO
Good Bye World!!!

 %%% JNIEnv attached : 00000206FF8E7B40

package com.home;

public class Main 

 static 
 System.loadLibrary("JNITest"); // Load native library hello.dll (Windows) or libhello.so (Unixes)
 // at runtime
 // This library contains a native method called sayHello()
 

 public static void main(String[] args) throws Exception 
 // TODO Auto-generated method stub

 System.out.println("Hello World!!!");

 new Main().sayHello();

 Thread.sleep(5000);

 System.out.println("Good Bye World!!!");

 

 // Declare an instance native method sayHello() which receives no parameter and returns void
 private native void sayHello();

// JNITest.cpp : Defines the exported functions for the DLL application.
//
#include "com_home_Main.h"
#include "stdafx.h"
#include <iostream>
#include <thread> 

static JavaVM *g_jVM = NULL;

using namespace std;
void foo()

 JNIEnv *jEnv = NULL;

 cout << "Hello FROM FOO" << endl;

 g_jVM->AttachCurrentThreadAsDaemon((void **)(&jEnv), NULL);
 if (jEnv == NULL)
 
 std::cout << "n !!! Failed to attach current thread with JVM !!! n";

 
 else
 
 std::cout << "n %%%t JNIEnv attached : " << (void *)jEnv;
 g_jVM->DetachCurrentThread();
 




extern "C"
// Implementation of the native method sayHello()
JNIEXPORT void JNICALL Java_com_home_Main_sayHello(JNIEnv *env, jobject thisObj) 
 cout << "Hello World from C++!" << endl;

 env->GetJavaVM(&g_jVM);

 std::thread *first = new std::thread(foo);

 return;

share|improve this question

edited Mar 25 at 1:32

Boris

asked Mar 25 at 1:20

BorisBoris

566628

share|improve this question

edited Mar 25 at 1:32

Boris

asked Mar 25 at 1:20

BorisBoris

566628

asked Mar 25 at 1:20

BorisBoris

566628

asked Mar 25 at 1:20

BorisBoris

566628