Java example source code file (EpollEventArray.java)

This example Java source code file (EpollEventArray.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

epoll_data_offset, epoll_event_size, epolleventarray, illegalargumentexception

The EpollEventArray.java Java example source code

/*
 * Copyright 2015 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.channel.epoll;

import io.netty.util.internal.PlatformDependent;

/**
 * This is an internal datastructure which can be directly passed to epoll_wait to reduce the overhead.
 *
 * typedef union epoll_data {
 *     void        *ptr;
 *     int          fd;
 *     uint32_t     u32;
 *     uint64_t     u64;
 * } epoll_data_t;
 *
 * struct epoll_event {
 *     uint32_t     events;      // Epoll events
 *     epoll_data_t data;        // User data variable
 * };
 *
 * We use {@code fd} if the {@code epoll_data union} to store the actual file descriptor of an
 * {@link AbstractEpollChannel} and so be able to map it later.
 */
final class EpollEventArray {
    // Size of the epoll_event struct
    private static final int EPOLL_EVENT_SIZE = Native.sizeofEpollEvent();
    // The offsiet of the data union in the epoll_event struct
    private static final int EPOLL_DATA_OFFSET = Native.offsetofEpollData();

    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;
        memoryAddress = allocate(length);
    }

    private static long allocate(int length) {
        return PlatformDependent.allocateMemory(length * EPOLL_EVENT_SIZE);
    }

    /**
     * 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;
        free();
        memoryAddress = allocate(length);
    }

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

    /**
     * Return the events for the {@code epoll_event} on this index.
     */
    int events(int index) {
        return PlatformDependent.getInt(memoryAddress + index * EPOLL_EVENT_SIZE);
    }

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