JNI

The native code for a JNI application is compiled into a shared library or executable that's loaded into the process address space.

The JNI specification requires that each native be able to create at least 16 local references.

A common JNI programming pitfall is to call a JNI method and to proceed without checking for exceptions once the call is complete.

It's possible to recompile your own JNI libraries with one of these tools to track a native memory leak in your code.

A thread must be attached to the VM before any other JNI calls can be made.

It recommended that you do not relax the EJB restrictions on using JNI in your application server, as this can compromise its robustness.

Some APIs can only be invoked from C code, if necessary, through the use of JNI or other coupling facilities.

The EJB specification forbids using JNI, as it compromises the stability, security, and scalability of the application server.

The goal is to help you recognize and steer clear of them so that you can write safe, effective JNI code that performs well from the start.

This generates a trace of the native methods called as well as the JNI callbacks that they make.

IBM's JVM implementation includes an option that turns on automatic JNI checks, at the cost of slower execution.

Does not support Java Native Interface (JNI), Raw Native Interface (RNI), and Remote Method Invocation (RMI).

Native operations should be grouped together whenever possible to reduce the number of JNI calls.

Note that it is beyond the scope of this article to provide a complete description of JNI.

If your application server allowed JNI, then an error in the JNI access could bring down the entire application server!

Handling exceptions natively in the JNI code itself, though unavoidable sometimes, leads to performance degradation.

JNI allows Java code that runs inside a JVM to interoperate with applications and libraries written in other programming languages.

The tutorial moves on to introduce the Java Native Interface (JNI), which is the technology of interest when working with the NDK.

Pinned objects are those that cannot be moved during heap compaction because of JNI (Java Native Interface) access to these objects.

It issues warnings when it sees code that doesn't conform to the specification and can help you find instances of the common JNI pitfalls.

A JVM implementing the JNI can allocate and store thread-local data in the area pointed to by the JNI interface pointer.

However, communication between JVM and native code is generally slow, thus too many JNI calls can degrade performance.

If you have your own JNI libraries, try stubbing them out entirely one at a time to determine if they are causing the leak.

The JDIC component code itself figures out which OS the application is being run on and calls the appropriate JNI function.

Offers a tutorial and detailed description of JNI features and programming techniques.

Class also maintains a JNI environment pointer at a thread-specific location.

JNI puts the interface pointer value at a location specified by its first parameter.

jni is of little use except when working with JNI and native libraries.

JNI allows native code (applications written in native languages such as C and C ) to call Java methods and vice versa.

This type of barrier processing is also required for internal JVM structures, including the JNI Global Reference list.

You're now aware of the top 10 JNI programming pitfalls and have learned some good practices for identifying them in existing or new code.

Yawning ['jni] and headache are the most common adverse reactions.

When a JNI invocation happens, it usually involves two process.

The JNI interface pointer, once obtained, should be stored in memory for later use.

Using the IBM JVM's -Xcheck: jni option as part of the standard development process can help you find coding errors much more easily.

The first switch is from a Java API layer to a Java native Interface (JNI) layer.

The utility is useful in environments where the VM is started using the JNI Invocation API rather than the standard Java launcher.

As we pointed out in our introduction, the use of JNI isn't sufficient to meet these needs.

The native code that runs in the same process space as the invoking JVM under JNI.

It is strongly recommended NOT to invoke Java code through JNI using user exits.

The first parameter is the JNI environment, frequently used with helper functions.

Not all the findings the JNI check reports are necessarily errors in the code.

This means is that you need to keep the JNI interface pointer in thread - local data as well .

The native may not make any JNI calls between these methods and may not block for any reason.

The Invocation API is part of the JNI specification.

Validate that there is a check for an exception after all JNI calls that can raise an exception.

JNI context for the main thread of the app.

List all the occurrences of JNI references in your application.

The JNI specification states that each JNIEnv is local to a thread.

Many of the JNI methods that natives can call can raise exceptions on the executing thread.

This article covers the 10 most common coding and design errors that users of the JNI make.

All native JNI methods should be declared in the Java code.

Enabling or disabling strict native call checking (-Xcheck: jni).

The JNI interface pointer is valid only in the current thread.

Don't think that you need to be an expert in native code or JNI or must know every OS.

The second switch is from a JNI layer to a kernel space.

Thus, you have to modify the signatures of existing functions to work with JNI.

JNI lets you call native code in the Java language, and vice versa.

The third file contains a Java proxy class that implements the interface by calling the JNI methods.

ikvm-native. dll: A unmanaged C library needed for the JNI interface.

Options such as JNI and other . Net to Java integration libraries were not chosen for a number of reasons.

ning just like a native method. Thus it can, among other things, issue JNI calls to.

A thread executing native code uses a JNIEnv to make JNI methods calls.

JNI's flexibility and power introduce the risk of programming practices that can lead to poor performance, bugs, and even program crashes.

No use of heap or JNI resources beyond the absolute minimum.

fjni tells gcj that native methods in your Java code are implemented using JNI.

There is no defined behavior if you want to use JNI to change final fields.

See the Resources section below for more information on JNI.

And in my case even the connectors from Tomcat to Apache and the database are pure Java, because they use sockets to interoperate, not JNI.

The second file contains JNI native declarations for each of the methods in the interface, shown in Listing 5

Additional information about JNI programming can be found in the following developerWorks articles

The JNI interface pointer can be obtained in two ways

Research of Platform Independent Programming Using JNI Technology

Discuss on Application of JNI Technology in Embedded Software Development

Validating new code against the JNI specification

Once the thread is done with JNI calls, it needs to release the interface pointer by calling

Implementation of JNI technology in smart cards

Performance of JNI Field and Method Operations

A string representing the method's signature in JNI syntax

You enable the JNI check option with the following command line

Analyzing and implementation of application's frame based on JNI technology

Use the following code to compile and create a JNI header file for Pipes. java

load and initialize a Java VM, return a JNI interface

Summary of JNI String Functions

Research of Microcomputer Data Gain Based on JNI Technology

For example, Listing 1 shows the JNI code required to call a static method