Netty 4 Bytebuffer WritableBytes 说明

Question

我正在尝试了解 ByteBuffer。下面是程序。

        ByteBuf heapBuff = Unpooled.buffer(18);
        System.out.println("writableBytes " + heapBuff.writableBytes());
        heapBuff.writeCharSequence("RAJKUMAR NATARAJAN TESTE", Charset.defaultCharset());
        System.out.println("readableBytes " + heapBuff.readableBytes());
        System.out.println("writableBytes " + heapBuff.writableBytes());

以上程序的输出是

        writableBytes 18
        readableBytes 24
        writableBytes 104

writableBytes的计算逻辑是什么

Answer 1

缓冲区写入将检查它们是否有足够的可写字节来容纳数据，如果没有，将在后台增加缓冲区的大小。这就是检查是否有足够的可写字节时调用的内容，也是容量增加的原因。如果将 24 加到 104 = 128，即 2 的幂。

AbstractByteBuf.class

final void ensureWritable0(int minWritableBytes) {
    ensureAccessible();
    if (minWritableBytes <= writableBytes()) {
        return;
    }

    if (minWritableBytes > maxCapacity - writerIndex) {
        throw new IndexOutOfBoundsException(String.format(
                "writerIndex(%d) + minWritableBytes(%d) exceeds maxCapacity(%d): %s",
                writerIndex, minWritableBytes, maxCapacity, this));
    }

    // Normalize the current capacity to the power of 2.
    int newCapacity = alloc().calculateNewCapacity(writerIndex + minWritableBytes, maxCapacity);

    // Adjust to the new capacity.
    capacity(newCapacity);
}

资源：

ByteBuf JavaDoc

AbstractByteBuf.class (github)

Netty 4 Bytebuffer WritableBytes 说明

Netty 4 Bytebuffer WritableBytes clarification

netty