彩票型网站建设,好看的个人网站主页,速度快的wordpress主机,订餐网站怎么做文章目录 1.概述2. ByteBuf 分类3. 代码实例3.1 常用方法3.1.1 创建ByteBuf3.1.2 写入字节3.1.3 扩容3.1.2.1 扩容实例3.1.2.2 扩容计算新容量代码 3.1.4 读取字节3.1.5 标记回退3.1.6 slice3.1.7 duplicate3.1.8 CompositeByteBuf3.1.9 retain release3.1.9.1 retain release3.1.9.1 retain release3.1.9.2 Netty TailContext release 3.2 完整实例 4. 参考文献 1.概述
ByteBuf 对字节进行操作
ByteBuf 四个基本属性
readerIndex 读指针字节数组读到哪了writerIndex 写指针字节数组写到哪了maxCapacity最大容量字节数组最大容量markedReaderIndex标记读指针resetReaderIndex方法可以把readerIndex修改为markedReaderIndex回退重新读数据markedWriterIndex 标记写指针resetReaderIndex方法可以把 writerIndex 修改为markedWriterIndex回退重新写数据
public abstract class AbstractByteBuf extends ByteBuf {int readerIndex;int writerIndex;private int markedReaderIndex;private int markedWriterIndex;private int maxCapacity;
}2. ByteBuf 分类
ByteBuf 分为
直接内存或堆内存Heap/Direct池化 和 非池化Pooled/Unpooled和 操作方式是否安全 Unsafe/非 Unsafe
ByteBuf 创建可以基于直接内存或堆内存
直接内存创建和销毁的代价昂贵但读写性能高少一次内存复制适合配合池化功能一起用直接内存对 GC 压力小因为这部分内存不受 JVM 垃圾回收的管理但也要注意及时主动释放
ByteBuf 池化 和 非池化
没有池化则每次都得创建新的 ByteBuf 实例这个操作对直接内存代价昂贵就算是堆内存也会增加 GC 压力有了池化则可以重用池中 ByteBuf 实例并且采用了与 jemalloc 类似的内存分配算法提升分配效率高并发时池化功能更节约内存减少内存溢出的可能
ByteBuf 操作方式是否安全 Unsafe/非 Unsafe
Unsafe表示每次调用 JDK 的 Unsafe 对象操作物理内存依赖 offset index 的方式操作数据非 Unsafe则不需要依赖 JDK 的 Unsafe 对象直接通过数组下标的方式操作数据
3. 代码实例
3.1 常用方法
3.1.1 创建ByteBuf
创建ByteBuf , 默认都是池化的 // 堆内存的ByteBufByteBuf bufferHeap ByteBufAllocator.DEFAULT.heapBuffer();// 直接内存的ByteBufByteBuf bufferDirect ByteBufAllocator.DEFAULT.directBuffer();System.out.println(bufferHeap);System.out.println(bufferDirect);3.1.2 写入字节 bufferHeap.writeBytes(new byte[]{1, 2, 3, 4});bufferDirect.writeBytes(new byte[]{1, 2, 3, 4});print(第一次写入, bufferHeap);print(第一次写入, bufferDirect);3.1.3 扩容
3.1.2.1 扩容实例
默认 256扩容加一倍到了4194304每次4194304 for (int i 0; i 100; i) {bufferHeap.writeBytes(new byte[]{1, 2, 3, 4});bufferDirect.writeBytes(new byte[]{1, 2, 3, 4});}print(批量写入扩容, bufferHeap);print(批量写入扩容, bufferDirect);3.1.2.2 扩容计算新容量代码
public int calculateNewCapacity(int minNewCapacity, int maxCapacity) {ObjectUtil.checkPositiveOrZero(minNewCapacity, minNewCapacity);if (minNewCapacity maxCapacity) {throw new IllegalArgumentException(String.format(minNewCapacity: %d (expected: not greater than maxCapacity(%d), minNewCapacity, maxCapacity));} else {int threshold 4194304;if (minNewCapacity 4194304) {return 4194304;} else {int newCapacity;if (minNewCapacity 4194304) {newCapacity minNewCapacity / 4194304 * 4194304;if (newCapacity maxCapacity - 4194304) {newCapacity maxCapacity;} else {newCapacity 4194304;}return newCapacity;} else {for(newCapacity 64; newCapacity minNewCapacity; newCapacity 1) {}return Math.min(newCapacity, maxCapacity);}}}
}3.1.4 读取字节 readByte(bufferHeap);readByte(bufferDirect);print(读取一个字节, bufferHeap);print(读取一个字节, bufferDirect);3.1.5 标记回退 bufferHeap.markReaderIndex();bufferDirect.markReaderIndex();readByte(bufferHeap);readByte(bufferDirect);print(读取一个字节, bufferHeap);print(读取一个字节, bufferDirect);System.out.println(回退);bufferHeap.resetReaderIndex();bufferDirect.resetReaderIndex();readByte(bufferHeap);readByte(bufferDirect);print(读取一个字节, bufferHeap);print(读取一个字节, bufferDirect);3.1.6 slice // 无参 slice 是从原始 ByteBuf 的 read index 到 write index 之间的内容进行切片// slice 和 bufferHeap 共享一块内存ByteBuf slice bufferHeap.slice();slice.setByte(0, 9);print(slice, slice);readByte(bufferHeap);3.1.7 duplicate // 内存拷贝不共享内存ByteBuf duplicate bufferHeap.duplicate();print(duplicate, duplicate);print(bufferHeap, bufferHeap);duplicate.writeBytes(new byte[]{5});print(duplicate, duplicate);print(bufferHeap, bufferHeap);3.1.8 CompositeByteBuf // CompositeByteBuf 是一个组合的 ByteBuf它内部维护了一个 Component 数组// 每个 Component 管理一个 ByteBuf记录了这个 ByteBuf 相对于整体偏移量等信息代表着整体中某一段的数据。// 优点对外是一个虚拟视图组合这些 ByteBuf 不会产生内存复制// 缺点复杂了很多多次操作会带来性能的损耗ByteBuf buf1 ByteBufAllocator.DEFAULT.buffer(5);buf1.writeBytes(new byte[]{1, 2, 3, 4, 5});ByteBuf buf2 ByteBufAllocator.DEFAULT.buffer(5);buf2.writeBytes(new byte[]{6, 7, 8, 9, 10});CompositeByteBuf buf3 ByteBufAllocator.DEFAULT.compositeBuffer();// true 表示增加新的 ByteBuf 自动递增 write index, 否则 write index 会始终为 0buf3.addComponents(true, buf1, buf2);print(buf3, buf3);3.1.9 retain release
3.1.9.1 retain release
Netty 这里采用了引用计数法来控制回收内存每个 ByteBuf 都实现了 ReferenceCounted 接口
每个 ByteBuf 对象的初始计数为 1调用 release 方法计数减 1如果计数为 0ByteBuf 内存被回收调用 retain 方法计数加 1表示调用者没用完之前其它 handler 即使调用了 release 也不会造成回收当计数为 0 时底层内存会被回收这时即使 ByteBuf 对象还在其各个方法均无法正常使用 bufferHeap.retain();bufferDirect.retain();bufferHeap.release();bufferDirect.release();print(release bufferHeap, bufferHeap);print(release bufferDirect, bufferDirect);bufferHeap.release();bufferDirect.release();print(release bufferHeap, bufferHeap);print(release bufferDirect, bufferDirect);bufferHeap.release();bufferDirect.release();print(release bufferHeap, bufferHeap);print(release bufferDirect, bufferDirect);3.1.9.2 Netty TailContext release
io.netty.channel.DefaultChannelPipeline.TailContext
io.netty.channel.DefaultChannelPipeline.TailContext#channelRead Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) {onUnhandledInboundMessage(ctx, msg);}io.netty.channel.DefaultChannelPipeline#onUnhandledInboundMessage(ChannelHandlerContext, Object) protected void onUnhandledInboundMessage(ChannelHandlerContext ctx, Object msg) {onUnhandledInboundMessage(msg);if (logger.isDebugEnabled()) {logger.debug(Discarded message pipeline : {}. Channel : {}.,ctx.pipeline().names(), ctx.channel());}}3.2 完整实例 import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
import io.netty.buffer.CompositeByteBuf;public class ByteBufStudy {public static void main(String[] args) {// 堆内存的ByteBufByteBuf bufferHeap ByteBufAllocator.DEFAULT.heapBuffer();// 直接内存的ByteBufByteBuf bufferDirect ByteBufAllocator.DEFAULT.directBuffer();System.out.println(bufferHeap);System.out.println(bufferDirect);bufferHeap.writeBytes(new byte[]{1, 2, 3, 4});bufferDirect.writeBytes(new byte[]{1, 2, 3, 4});print(第一次写入, bufferHeap);print(第一次写入, bufferDirect);for (int i 0; i 100; i) {bufferHeap.writeBytes(new byte[]{1, 2, 3, 4});bufferDirect.writeBytes(new byte[]{1, 2, 3, 4});}print(批量写入扩容, bufferHeap);print(批量写入扩容, bufferDirect);readByte(bufferHeap);readByte(bufferDirect);print(读取一个字节, bufferHeap);print(读取一个字节, bufferDirect);bufferHeap.markReaderIndex();bufferDirect.markReaderIndex();readByte(bufferHeap);readByte(bufferDirect);print(读取一个字节, bufferHeap);print(读取一个字节, bufferDirect);System.out.println(回退);bufferHeap.resetReaderIndex();bufferDirect.resetReaderIndex();readByte(bufferHeap);readByte(bufferDirect);print(读取一个字节, bufferHeap);print(读取一个字节, bufferDirect);// 无参 slice 是从原始 ByteBuf 的 read index 到 write index 之间的内容进行切片// slice 和 bufferHeap 共享一块内存ByteBuf slice bufferHeap.slice();slice.setByte(0, 9);print(slice, slice);readByte(bufferHeap);// 内存拷贝不共享内存ByteBuf duplicate bufferHeap.duplicate();print(duplicate, duplicate);print(bufferHeap, bufferHeap);duplicate.writeBytes(new byte[]{5});print(duplicate, duplicate);print(bufferHeap, bufferHeap);// CompositeByteBuf 是一个组合的 ByteBuf它内部维护了一个 Component 数组// 每个 Component 管理一个 ByteBuf记录了这个 ByteBuf 相对于整体偏移量等信息代表着整体中某一段的数据。// 优点对外是一个虚拟视图组合这些 ByteBuf 不会产生内存复制// 缺点复杂了很多多次操作会带来性能的损耗ByteBuf buf1 ByteBufAllocator.DEFAULT.buffer(5);buf1.writeBytes(new byte[]{1, 2, 3, 4, 5});ByteBuf buf2 ByteBufAllocator.DEFAULT.buffer(5);buf2.writeBytes(new byte[]{6, 7, 8, 9, 10});CompositeByteBuf buf3 ByteBufAllocator.DEFAULT.compositeBuffer();// true 表示增加新的 ByteBuf 自动递增 write index, 否则 write index 会始终为 0buf3.addComponents(true, buf1, buf2);print(buf3, buf3);bufferHeap.retain();bufferDirect.retain();bufferHeap.release();bufferDirect.release();print(release bufferHeap, bufferHeap);print(release bufferDirect, bufferDirect);bufferHeap.release();bufferDirect.release();print(release bufferHeap, bufferHeap);print(release bufferDirect, bufferDirect);bufferHeap.release();bufferDirect.release();print(release bufferHeap, bufferHeap);print(release bufferDirect, bufferDirect);}public static void print(String prefix, ByteBuf buffer) {System.out.printf(%s readerIndex : %s writerIndex : %s maxCapacity : %s capacity : %s %n,prefix, buffer.readerIndex(), buffer.writerIndex(), buffer.maxCapacity(), buffer.capacity());}public static void readByte(ByteBuf buffer) {System.out.printf(读取一个字节: %s %n, buffer.readByte());}
}4. 参考文献
黑马 Netty教程拉钩教育 Netty课程 若地老师
