Netty学习——源码篇11 Netty非池化内存分配

1 堆内内存的分配

        现在来看UnpooledByteBufAllocator的内存分配原理。首先是heapBuffer的分配逻辑，newHeapBuffer方法的代码如下：

    @Override
    protected ByteBuf newHeapBuffer(int initialCapacity, int maxCapacity) {
        return PlatformDependent.hasUnsafe() ? new UnpooledUnsafeHeapByteBuf(this, initialCapacity, maxCapacity)
                : new UnpooledHeapByteBuf(this, initialCapacity, maxCapacity);
    }

        通过调用PlatformDependent.hasUnsafe()方法来判断操作系统是否支持Unsafe，如果支持Unsafe则创建UnpooledUnsafeHeapByteBuf类，否则创建UnpooledHeapByteBuf类。先看一下UnpooledUnsafeHeapByteBuf的构造器会进行哪些操作，代码如下：

final class UnpooledUnsafeHeapByteBuf extends UnpooledHeapByteBuf {

    /**
     * Creates a new heap buffer with a newly allocated byte array.
     *
     * @param initialCapacity the initial capacity of the underlying byte array
     * @param maxCapacity the max capacity of the underlying byte array
     */
    UnpooledUnsafeHeapByteBuf(ByteBufAllocator alloc, int initialCapacity, int maxCapacity) {
        super(alloc, initialCapacity, maxCapacity);
    }
}

        发现UnpooledUnsafeHeapByteBuf继承了UnpooledHeapByte,并且在UnpooledUnsafeHeapByteBuf的构造器中直接调用了super方法，也就是其父类UnpooledHeapByte的构造方法。看一下UnpooledHeapByte的构造方法。

public class UnpooledHeapByteBuf extends AbstractReferenceCountedByteBuf {

    private final ByteBufAllocator alloc;
    byte[] array;
    private ByteBuffer tmpNioBuf;

    /**
     * Creates a new heap buffer with a newly allocated byte array.
     *
     * @param initialCapacity the initial capacity of the underlying byte array
     * @param maxCapacity the max capacity of the underlying byte array
     */
    protected UnpooledHeapByteBuf(ByteBufAllocator alloc, int initialCapacity, int maxCapacity) {
        this(alloc, new byte[initialCapacity], 0, 0, maxCapacity);
    }

    protected UnpooledHeapByteBuf(ByteBufAllocator alloc, byte[] initialArray, int maxCapacity) {
        this(alloc, initialArray, 0, initialArray.length, maxCapacity);
    }

    private UnpooledHeapByteBuf(
            ByteBufAllocator alloc, byte[] initi