CpuFeaturesJava

Java bindings for Google cpu_features

---

Even though Java is a "write once, run anywhere" language, often a library will still want to use a native library, which is not only OS-specific but also host-specific. These libraries may be compiled with different CPU flags enabled, such as AVX2 or F16C, to utilise different CPU features. When loading a library from Java, the program has no clue which features may be supported, so must rely on the most accessible version - which is often the slowest. Using cpu_features, Java programs can detect which features the host CPU supports and load different native libraries based on this info.

Note: Version 2.0 of this library uses the (currently unstable) Java foreign function interface, and will require Java 19 as well as the command line arguments --enable-preview --enable-native-access=ALL-UNNAMED. The previous version, using JNI and Java 15, is still available under io.github.aecsocket:cpu-features-jni:1.0.1.

Coverage

Platforms:

• Linux (x86)
• Windows (x86)
• MacOS (x86)

Architectures:

• AArch64
• ARM
• X86

Usage

repositories {
    mavenCentral()
}

dependencies {
    implementation("io.github.aecsocket", "cpu-features-java", "VERSION")
    // native libraries
    runtimeOnly("io.github.aecsocket", "cpu-features-java-natives-linux-x86", "VERSION")
    runtimeOnly("io.github.aecsocket", "cpu-features-java-natives-windows-x86", "VERSION")
    runtimeOnly("io.github.aecsocket", "cpu-features-java-natives-macos-x86", "VERSION")
}

Usage is very similar to cpu_features. See HelloCpuFeatures.java to get a minimal implementation.

Getting CPU info

// If using the native library dependencies:
CpuFeatures.load();
// Otherwise load the libraries yourself:
// System.loadLibrary("cpu_features");

// CpuFeatures is the entry point to the application
CpuArchitecture arch = CpuFeatures.getArchitecture();
switch (arch) {
    case ARM -> {
        // The various -Info classes hold all CPU info
        ArmInfo info = ArmInfo.get();
        System.out.println(info.implementer);
    }
    case X86 -> {
        X86Info info = X86Info.get()
        System.out.println(info.vendor);
    }
    // ...
}

Querying CPU features

public static boolean useAVX2 = false;

public static void init() {
    X86Info info = X86Info.get();
    // Prefer accessing `features` directly over using an enum
    useAVX2 = info.features().avx2();
    // useAVX2 = X86Feature.AVX2.in(info.features());

    Set<X86Feature> features = info.featureSet();
    System.out.println("features: " + features);
}

Building from source

On Windows, you need Ninja installed.

git clone https://github.com/aecsocket/cpu-features-java
cd cpu-features-java
git submodule update --init
./gradlew build