EpollEventArray Class — netty Architecture

Source Code

transport-classes-epoll/src/main/java/io/netty/channel/epoll/EpollEventArray.java lines 43–127

@UnstableApi
public final class EpollEventArray {
    // Size of the epoll_event struct
    private static final int EPOLL_EVENT_SIZE = Native.sizeofEpollEvent();
    // The offset of the data union in the epoll_event struct
    private static final int EPOLL_DATA_OFFSET = Native.offsetofEpollData();

    private CleanableDirectBuffer cleanable;
    private ByteBuffer memory;
    private long memoryAddress;
    private int length;

    EpollEventArray(int length) {
        if (length < 1) {
            throw new IllegalArgumentException("length must be >= 1 but was " + length);
        }
        this.length = length;
        cleanable = Buffer.allocateDirectBufferWithNativeOrder(calculateBufferCapacity(length));
        memory = cleanable.buffer();
        memoryAddress = Buffer.memoryAddress(memory);
    }

    /**
     * Return the {@code memoryAddress} which points to the start of this {@link EpollEventArray}.
     */
    long memoryAddress() {
        return memoryAddress;
    }

    /**
     * Return the length of the {@link EpollEventArray} which represent the maximum number of {@code epoll_events}
     * that can be stored in it.
     */
    int length() {
        return length;
    }

    /**
     * Increase the storage of this {@link EpollEventArray}.
     */
    void increase() {
        // double the size
        length <<= 1;
        // There is no need to preserve what was in the memory before.
        CleanableDirectBuffer buffer = Buffer.allocateDirectBufferWithNativeOrder(calculateBufferCapacity(length));
        cleanable.clean();
        cleanable = buffer;
        memory = buffer.buffer();
        memoryAddress = Buffer.memoryAddress(buffer.buffer());
    }

    /**
     * Free this {@link EpollEventArray}. Any usage after calling this method may segfault the JVM!
     */
    void free() {
        cleanable.clean();
        memoryAddress = 0;
    }

    /**
     * Return the events for the {@code epoll_event} on this index.
     */
    int events(int index) {
        return getInt(index, 0);
    }

    /**
     * Return the file descriptor for the {@code epoll_event} on this index.
     */
    int fd(int index) {
        return getInt(index, EPOLL_DATA_OFFSET);
    }

    private int getInt(int index, int offset) {
        if (PlatformDependent.hasUnsafe()) {
            long n = (long) index * EPOLL_EVENT_SIZE;
            return PlatformDependent.getInt(memoryAddress + n + offset);
        }
        return memory.getInt(index * EPOLL_EVENT_SIZE + offset);
    }