标签：没有 request thread not init red turn 创建 ted
PooledByteBuf的初始化过程分为两个步骤：创建实例；初始化内存。这两个步骤的代码如下：
protected PooledByteBuf(Recycler.Handle recyclerHandle, int maxCapacity) {
super(maxCapacity);
this.recyclerHandle = recyclerHandle;
}
void init(PoolChunk<T> chunk, long handle, int offset, int length, int maxLength, PoolThreadCache cache) {
init0(chunk, handle, offset, length, maxLength, cache);
}
private void init0(PoolChunk<T> chunk, long handle, int offset, int length, int maxLength, PoolThreadCache cache) {
assert handle >= 0;
assert chunk != null;
this.chunk = chunk;
memory = chunk.memory;
allocator = chunk.arena.parent;
this.cache = cache;
this.handle = handle;
this.offset = offset;
this.length = length;
this.maxLength = maxLength;
tmpNioBuf = null;
}
创建实例时调用的构造方法只是为maxCapacity和recyclerHandler属性赋值，构造方法是protected，不打算暴露到外面。派生类都提供了newInstance方法创建实例，以PooledHeapByteBuf为例，它的newInstance方法实现如下：
1 private static final Recycler<PooledHeapByteBuf> RECYCLER = new Recycler<PooledHeapByteBuf>() {
2 @Override
3 protected PooledHeapByteBuf newObject(Handle handle) {
4 return new PooledHeapByteBuf(handle, 0);
5 }
6 };
7
8 static PooledHeapByteBuf newInstance(int maxCapacity) {
9 PooledHeapByteBuf buf = RECYCLER.get();
10 buf.reuse(maxCapacity);
11 return buf;
12 }
这里的newInstance使用RECYCLER创建实例对象。Recycler<T>是一个轻量级的，支持循环使用的对象池。当对象池中没有可用对象时，会在第4行使用构造方法创建一个新的对象。
init调用init0初始化数据内存，init0方法为几个内存相关的关键属性赋值:
内存初始化完成之后，这个PooledByteBuf可使用的内存范围是memory内存中[offset, offset+length)。idx方法可以把ByteBuf的索引转换成memory的索引:
1 protected final int idx(int index) {
2 return offset + index;
3 }
和前面讲过的ByteBuf实现一样，PooledByteBuf也需要使用capacity(int newCapacity)改变内存大小，也会涉及到把数据从旧内存中复制到新内存的问题。也就是说，要解决的问题是一样的，只是具体实现的差异。
1 @Override
2 public final ByteBuf capacity(int newCapacity) {
3 checkNewCapacity(newCapacity);
4
5 // If the request capacity does not require reallocation, just update the length of the memory.
6 if (chunk.unpooled) {
7 if (newCapacity == length) {
8 return this;
9 }
10 } else {
11 if (newCapacity > length) {
12 if (newCapacity <= maxLength) {
13 length = newCapacity;
14 return this;
15 }
16 } else if (newCapacity < length) {
17 if (newCapacity > maxLength >>> 1) {
18 if (maxLength <= 512) {
19 if (newCapacity > maxLength - 16) {
20 length = newCapacity;
21 setIndex(Math.min(readerIndex(), newCapacity), Math.min(writerIndex(), newCapacity));
22 return this;
23 }
24 } else { // > 512 (i.e. >= 1024)
25 length = newCapacity;
26 setIndex(Math.min(readerIndex(), newCapacity), Math.min(writerIndex(), newCapacity));
27 return this;
28 }
29 }
30 } else {
31 return this;
32 }
33 }
34
35 // Reallocation required.
36 chunk.arena.reallocate(this, newCapacity, true);
37 return this;
38 }
netty源码解解析(4.0)-24 ByteBuf基于内存池的内存管理
标签：没有 request thread not init red turn 创建 ted
原文地址：https://www.cnblogs.com/aa1212/p/11706352.html
