public abstract class ArrayPool<T> { public static ArrayPool<T> Create() { // 堆代码 duidaima.com return new ConfigurableArrayPool<T>(); } } internal sealed class ConfigurableArrayPool<T> : ArrayPool<T> { private sealed class Bucket { internal readonly int _bufferLength; private readonly T[][] _buffers; private int _index; } private readonly Bucket[] _buckets; //bucket数组 }3. 为什么每一个 bucket 里都有 50 个 buffer[]
internal sealed class ConfigurableArrayPool<T> : ArrayPool<T> { internal ConfigurableArrayPool() : this(1048576, 50) { } internal ConfigurableArrayPool(int maxArrayLength, int maxArraysPerBucket) { int num = Utilities.SelectBucketIndex(maxArrayLength); Bucket[] array = new Bucket[num + 1]; for (int i = 0; i < array.Length; i++) { array[i] = new Bucket(Utilities.GetMaxSizeForBucket(i), maxArraysPerBucket, id); } _buckets = array; } }4. bucket 中 buffer[].length 为什么依次是 16,32,64 ...
internal ConfigurableArrayPool(int maxArrayLength, int maxArraysPerBucket) { Bucket[] array = new Bucket[num + 1]; for (int i = 0; i < array.Length; i++) { array[i] = new Bucket(Utilities.GetMaxSizeForBucket(i), maxArraysPerBucket, id); } } internal static int GetMaxSizeForBucket(int binIndex) { return 16 << binIndex; }5. 初始化时 bucket 到底有多少个?
maxArrayLength=1048576 = 2的20次方 buffer.length= 16 = 2的4次方最后的算法就是取次方的差值:bucket[].length= 20 - 4 + 1 = 17,换句话说最后一个 bucket 下的 buffer[].length=1048576,详细代码请参考 SelectBucketIndex() 方法。
internal sealed class ConfigurableArrayPool<T> : ArrayPool<T> { internal ConfigurableArrayPool(): this(1048576, 50) { } internal ConfigurableArrayPool(int maxArrayLength, int maxArraysPerBucket) { int num = Utilities.SelectBucketIndex(maxArrayLength); Bucket[] array = new Bucket[num + 1]; for (int i = 0; i < array.Length; i++) { array[i] = new Bucket(Utilities.GetMaxSizeForBucket(i), maxArraysPerBucket, id); } _buckets = array; } internal static int SelectBucketIndex(int bufferSize) { return BitOperations.Log2((uint)(bufferSize - 1) | 0xFu) - 3; } }到这里我相信你对 ArrayPool 的池化架构思路已经搞明白了,接下来看下如何申请和归还 buffer[]。
class Program { static void Main(string[] args) { // 堆代码 duidaima.com var arrayPool = ArrayPool<int>.Create(); var bytes = arrayPool.Rent(10); for (int i = 0; i < bytes.Length; i++) bytes[i] = 10; arrayPool.Return(bytes); Console.ReadLine(); } }
有了代码和图之后,再稍微捋一下流程。
internal T[] Rent() { T[][] buffers = _buffers; T[] array = null; bool lockTaken = false; bool flag = false; try { if (_index < buffers.Length) { array = buffers[_index]; buffers[_index++] = null; flag = array == null; } } if (flag) { array = new T[_bufferLength]; } return array; }这里有一个坑,那就是你以为借了 byte[10],现实给你的是 byte[16],这里稍微注意一下。当用 ArrayPool.Return 归还 byte[16] 时, 很明显看到它落到了第一个bucket的第一个buffer[]上,参考如下简化后的代码:
internal void Return(T[] array) { if (_index != 0) { _buffers[--_index] = array; } }这里也有一个值得注意的坑,那就是还回去的 byte[16] 里面的数据默认是不会清掉的,从上面的代码也是可以看出来的,要想做清理,需要在 Return 方法中指定 clearArray=true,参考如下代码:
public override void Return(T[] array, bool clearArray = false) { int num = Utilities.SelectBucketIndex(array.Length); if (num < _buckets.Length) { if (clearArray) { Array.Clear(array, 0, array.Length); } _buckets[num].Return(array); } }