FFM (Foreign Function and Memory) Stdlib Example

Published at

11/7/2024

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2 categories in total

FFM is the new API trying to replace JNI and jep is here It is basically calling calling functions outside of JVM or accessing memory not managed by JVM. I wanted to test can FFM beat regular Java API, below you can find a simple test doing math sin with FFM and with regular Math.sin

import java.lang.foreign.FunctionDescriptor;
import java.lang.foreign.Linker;
import java.lang.foreign.MemorySegment;
import java.lang.foreign.SymbolLookup;
import java.lang.foreign.ValueLayout;

public class FFMSinTest {
    public static void main(String[] args) throws Throwable {
        Linker linker = Linker.nativeLinker();
        SymbolLookup stdlib = linker.defaultLookup();

        // Locate the "sin" function in the C math library
        MemorySegment sinAddress = stdlib.find("sin").orElseThrow();
        FunctionDescriptor descriptor = FunctionDescriptor.of(ValueLayout.JAVA_DOUBLE, ValueLayout.JAVA_DOUBLE);
        var sinHandle = linker.downcallHandle(sinAddress, descriptor);

        double angle = Math.PI / 4; // 45 degrees in radians

        // Timing Java's Math.sin()
        long javaStartTime = System.nanoTime();
        for (int i = 0; i < 1_000_000; i++) {
            double result = Math.sin(angle);
        }
        long javaEndTime = System.nanoTime();
        long javaDuration = javaEndTime - javaStartTime;

        // Timing C sin via FFM
        long ffmStartTime = System.nanoTime();
        for (int i = 0; i < 1_000_000; i++) {
            double result = (double) sinHandle.invoke(angle);
        }
        long ffmEndTime = System.nanoTime();
        long ffmDuration = ffmEndTime - ffmStartTime;

        System.out.println("Java Math.sin() took: " + javaDuration / 1_000_000.0 + " ms");
        System.out.println("C sin (FFM) took: " + ffmDuration / 1_000_000.0 + " ms");
    }
}

And result is

Java Math.sin() took: 4.8677 ms
C sin (FFM) took: 78.9172 ms

In my laptop, lesson is “calling outside JVM is not a cheap process” 🤓

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FFM (Foreign Function and Memory) Stdlib Example