1.Heap Buffer(堆缓冲区)
2.Direct Buffer(直接缓冲区)
3.Composite Buffer(复合缓冲区)
4.PooledByteBuf 池缓冲
readerInex 当前读取索引
writerIndex 当前写索引
0~readerInex 之间被视为 discard,调用 discardReadBytes() 会释放空间 @Override
public ByteBuf discardReadBytes() {
ensureAccessible();
if (readerIndex == 0) {
return this;
} if (readerIndex != writerIndex) {
setBytes(0, this, readerIndex, writerIndex - readerIndex);
writerIndex -= readerIndex;
adjustMarkers(readerIndex);
readerIndex = 0;
} else {
adjustMarkers(readerIndex);
writerIndex = readerIndex = 0;
}
return this;
} @Override
public ByteBuf ensureWritable(int minWritableBytes) {
if (minWritableBytes < 0) {
throw new IllegalArgumentException(String.format(
"minWritableBytes: %d (expected: >= 0)", minWritableBytes));
} if (minWritableBytes <= writableBytes()) {
return this;
}
//写入数据长度大于剩余长度（默认int max - wirter）
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.
//计算新空间大小
int newCapacity = calculateNewCapacity(writerIndex + minWritableBytes); // Adjust to the new capacity.
//不同类型扩展实现 处理过程实际是直接修改JDK ByteBuffer
capacity(newCapacity);
return this;
} private int calculateNewCapacity(int minNewCapacity) {
final int maxCapacity = this.maxCapacity;
final int threshold = 1048576 * 4; // 4 MiB page if (minNewCapacity == threshold) {
return threshold;
} // If over threshold, do not double but just increase by threshold.
//当超过4M时，直接扩展4M空间
if (minNewCapacity > threshold) {
int newCapacity = minNewCapacity / threshold * threshold;
if (newCapacity > maxCapacity - threshold) {
newCapacity = maxCapacity;
} else {
newCapacity += threshold;
}
return newCapacity;
} // Not over threshold. Double up to 4 MiB, starting from 64.
//以双倍扩展空间
int newCapacity = 64;
while (newCapacity < minNewCapacity) {
newCapacity <<= 1;
} return Math.min(newCapacity, maxCapacity);
}