com.github.foobar27.nativeinitializer.NativeInitializer Maven / Gradle / Ivy

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Specify how native libraries should be loaded

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package com.github.foobar27.nativeinitializer;

import java.io.IOException;
import java.util.function.Supplier;

public final class NativeInitializer implements Supplier {
    private NativeLoader loader; // does not need to be volatile
    private final Supplier initializer;
    private final Object monitor = new Object();


    private volatile boolean initialized;
    private T value; // does not need to be volatile

    public NativeInitializer(NativeLoader loader, Supplier initializer) {
        this.initializer = initializer;
        this.loader = loader;
    }

    public void setNativeLoader(NativeLoader loader) throws NativeLoaderAlreadyInitializedException {
        if (initialized) {
            throw new NativeLoaderAlreadyInitializedException();
        }
        this.loader = loader;
    }

    @Override
    public T get() {
        if (!initialized) {
            synchronized (monitor) {
                // double-checked locking
                if (!initialized) {
                    try {
                        loader.load();
                    } catch (IOException e) {
                        throw new NativeLoaderException(e);
                    }
                    T t = initializer.get();
                    value = t;
                    initialized = true;
                    return t;
                }
            }
        }
        // We will read a non-volatile value here.
        // However just before we already read 'initialize', which is also volatile.
        // Thus we don't need to make 'value' volatile too.
        return value;
    }

}