Foreign Function and Memory API in Java

Last Updated : 08 Jun, 2023

Foreign Function Interface (FFI) and Memory API in Java provide mechanisms for Java programs to interact with code written in other languages, such as C or C++. This allows developers to leverage existing native libraries or access low-level system functionality. FFI enables Java programs to call native functions, while the Memory API allows efficient memory management and data exchange between Java and native code.

Concept with Proper Examples and Approach

To illustrate the concept of FFI and Memory API in Java, let’s consider a scenario where we have a native library written in C that performs complex mathematical computations. We want to leverage this library in our Java application.

1. Set up the native library: First, we need to compile the C code into a shared library that can be loaded by Java. This step varies depending on the platform but generally involves using a compiler like GCC or Clang to generate a shared library file (e.g., a .dll file on Windows or a .so file on Linux).

2. Declare the native functions: In Java, we use the native keyword to declare a method that will be implemented in native code. We also need to specify the library from which the method will be loaded using the @native annotation. Here’s an example:

Java

import jdk.incubator.foreign.*; 
  
public class MathLibrary { 
    @CFunction( 
        library = "mathlib", 
        name = "calculateSquareRoot", 
        cdefine = "double calculateSquareRoot(double)"
    ) 
    private static native double calculateSquareRoot(double value); 
  
    public static void main(String[] args) { 
        double result = calculateSquareRoot(16.0); 
        System.out.println("Square root: " + result); 
    } 
  
    static { 
        LibraryLoader.load(); 
    } 
} 

In the example above, we define a native method called calculateSquareRoot that takes a double value as a parameter and returns a double. The @CFunction annotation specifies the library name, function name, and C function signature.

3. Load the native library: To load the native library at runtime, we use the LibraryLoader.load() method. This ensures that the library is available when the native method is called. The LibraryLoader class is part of the jdk.incubator.foreign package.

4. Compile and run the Java program: Compile the Java code using the javac command, and then run it using the java command. Make sure that the native library file is accessible to the Java runtime by either placing it in the same directory or specifying its path using the java.library.path system property.

5. Linking with native code: When the calculateSquareRoot method is invoked, the Java program will make a call to the native function provided by the C library. The native code will execute the required computation and return the result to the Java program.

Another Example of demonstrating the Foreign Memory Access (FMA) API

Java

// Example demonstrating the Foreign Function Interface (FFI) 
import jdk.incubator.foreign.*; 
  
public class ForeignFunctionExample { 
    public static void main(String[] args) { 
        try (LibraryLookup libraryLookup = LibraryLookup.ofDefault()) { 
            // Define the function signature (accepting two longs and returning a long) 
            FunctionDescriptor descriptor = FunctionDescriptor.of(CLinker.C_LONG, CLinker.C_LONG, CLinker.C_LONG); 
              
            // Lookup the shared library containing the function 
            SymbolLookup symbolLookup = libraryLookup.lookup("shared_library_name"); 
              
            // Retrieve the function handle 
            FunctionHandle addFunction = symbolLookup.lookup("add").get().toFunctionHandle(descriptor); 
              
            // Invoke the function with  
              // arguments and print the result 
            long result = addFunction.invokeExact(10, 20); 
            System.out.println("Result: " + result); 
        } 
    } 
} 

By leveraging the FFI and Memory API in Java, developers can combine the power of native code with the ease and portability of the Java platform, enabling them to optimize performance-critical parts of their applications or integrate with existing native libraries seamlessly.