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ByteBuf 分类
Pooled: 每次申请内存都是从曾经调配好的内存池中取
Unpooled: 每次申请内存都重新分配
Heap: 应用 jvm 的堆内存
Direct: 操作系统间接内存
Unsafe: 调用 native 办法间接操作内存
非 Unsafe: 通过 jdk 的 api 间接操作内存
Unsafe 形式: 调用 jdk 的 unsafe 实例，依据根底偏移量 +index 算出总偏移量
static byte getByte(byte[] data, int index) {return UNSAFE.getByte(data, BYTE_ARRAY_BASE_OFFSET + index);
}非 Unsafe 形式: 就是通过数组下标获取
static byte getByte(byte[] memory, int index) {return memory[index];
}Unsafe 与下面两种分类形式不同，用户无奈决定用哪种形式；是否选用 unsafe 是由 Netty 判断能不能拿到底层的 unsafe 决定的。
if (PlatformDependent.hasUnsafe()) {buf = UnsafeByteBufUtil.newUnsafeDirectByteBuf(this, initialCapacity, maxCapacity);
} else {buf = new UnpooledDirectByteBuf(this, initialCapacity, maxCapacity);
}UnpooledByteBufAllocator 调配形式比较简单，就是每次申请内存的时候都重新分配一块新的内存返回。
重点看 PooledByteBufAllocator 内存调配流程
PooledByteBufAllocator 分配内存流程
以堆外内存非配为例
protected ByteBuf newDirectBuffer(int initialCapacity, int maxCapacity) {
// 拿到线程独有的 PoolThreadCache
PoolThreadCache cache = threadCache.get();
PoolArena<ByteBuffer> directArena = cache.directArena;
ByteBuf buf;
if (directArena != null) {buf = directArena.allocate(cache, initialCapacity, maxCapacity);
} else {if (PlatformDependent.hasUnsafe()) {buf = UnsafeByteBufUtil.newUnsafeDirectByteBuf(this, initialCapacity, maxCapacity);
} else {buf = new UnpooledDirectByteBuf(this, initialCapacity, maxCapacity);
}
}
return toLeakAwareBuffer(buf);
}先通过 threadCache 拿到一个 PoolThreadCache 类型的属性，threadCache 是 PoolThreadLocalCache 类型的，PoolThreadLocalCache 继承自 netty 自定义的 FastThreadLocal，相似 jdk 的 ThreadLocal，每个线程都有本人的 PoolThreadLocalCache，这样每个线程也就有本人的 PoolThreadCache。
PoolThreadCache 次要有两块区域，arena 和 cache
通过 PoolThreadCache 分配内存时，会先从 cache 获取，cache 是之前被应用过被回收的内存；
cache 获取不到，就从 arena 开拓一块内存，用完后再回收到 cache，不便下次间接从 cache 获取。
cache 局部是由多个 MemoryRegionCache 类型的数组组织起来的。不同数组下标代表不同的 MemoryRegionCache 内存规格。
MemoryRegionCache 里有一个队列，队列元素 Entry 蕴含一个 chunk 和一个 handle，chunk 是一块内存区域，而后通过 handle 能够定位到这个 Entry 它所援用的内存地位。
所以整个 PoolThreadCache 的 cache 局部的构造如下:
队列元素 Entry 代表一块对应大小的可分配内存。
ByteBufAllocator 内存调配
在 PooledByteBufAllocator 构造函数里，会创立两个 PoolArena 类型的数组，别离用于堆内和堆外
heapArenas = newArenaArray(nHeapArena);
directArenas = newArenaArray(nDirectArena);nHeapArena 默认状况下是 2*CPU 核数
final int defaultMinNumArena = runtime.availableProcessors() * 2;
这个应该是跟 NioEventLoopGroup 无关，默认 workGroup 会创立 2*CPU 核数 个 NioEventLoop，这样就能保障每个 NioEventLoop 线程都有一个本人独享的 Arena 防止线程争用，不必加锁。
接着下面的 directArena.allocate()办法
PooledByteBuf<T> allocate(PoolThreadCache cache, int reqCapacity, int maxCapacity) {
// 获取一个 PooledByteBuf 对象，如果对象池里有间接拿来用，否则就创立
PooledByteBuf<T> buf = newByteBuf(maxCapacity);
// 在 PoolThreadCache 里分配内存
allocate(cache, buf, reqCapacity);
return buf;
}allocate()办法先尝试从缓存中调配，也就是命中缓存；
如果失败，再从 arena 里开拓一块内存调配
命中缓存调配流程
- 找到对应 size 的 MemoryRegionCache
- 从队列中弹出一个 entry 给 ByteBuf 初始化
- 将弹出的 entry 扔到对象池复用
在 PoolThreadCache 里分配内存时，都是先尝试从缓存上进行调配，如果缓存上没有适合的，就在 arena 开拓一块内存。
内存规格
private void allocate(PoolThreadCache cache, PooledByteBuf<T> buf, final int reqCapacity) {
// 对申请的内存大小进行规格化
final int normCapacity = normalizeCapacity(reqCapacity);
// 依据申请内存大小进行调配
if (isTinyOrSmall(normCapacity)) { // capacity < pageSize
int tableIdx;
PoolSubpage<T>[] table;
boolean tiny = isTiny(normCapacity);
if (tiny) { // < 512
if (cache.allocateTiny(this, buf, reqCapacity, normCapacity)) {
// was able to allocate out of the cache so move on
return;
}
tableIdx = tinyIdx(normCapacity);
table = tinySubpagePools;
} else {if (cache.allocateSmall(this, buf, reqCapacity, normCapacity)) {
// was able to allocate out of the cache so move on
return;
}
tableIdx = smallIdx(normCapacity);
table = smallSubpagePools;
}
final PoolSubpage<T> head = table[tableIdx];
synchronized (head) {
final PoolSubpage<T> s = head.next;
// 示意以后链表没有元素
if (s != head) {
assert s.doNotDestroy && s.elemSize == normCapacity;
long handle = s.allocate();
assert handle >= 0;
s.chunk.initBufWithSubpage(buf, handle, reqCapacity);
if (tiny) {allocationsTiny.increment();
} else {allocationsSmall.increment();
}
return;
}
}
allocateNormal(buf, reqCapacity, normCapacity);
return;
}
if (normCapacity <= chunkSize) {if (cache.allocateNormal(this, buf, reqCapacity, normCapacity)) {
// was able to allocate out of the cache so move on
return;
}
allocateNormal(buf, reqCapacity, normCapacity);
} else {
// Huge allocations are never served via the cache so just call allocateHuge
allocateHuge(buf, reqCapacity);
}
}以 tiny 类型的内存调配为例
boolean allocateTiny(PoolArena<?> area, PooledByteBuf<?> buf, int reqCapacity, int normCapacity) {return allocate(cacheForTiny(area, normCapacity), buf, reqCapacity);
}
private MemoryRegionCache<?> cacheForTiny(PoolArena<?> area, int normCapacity) {int idx = PoolArena.tinyIdx(normCapacity);
if (area.isDirect()) {return cache(tinySubPageDirectCaches, idx);
}
return cache(tinySubPageHeapCaches, idx);
}
// tinyIdx 办法间接把 normCapacity/16
static int tinyIdx(int normCapacity) {return normCapacity >>> 4;}
private static <T> MemoryRegionCache<T> cache(MemoryRegionCache<T>[] cache, int idx) {if (cache == null || idx > cache.length - 1) {return null;}
// 拿到 MemoryRegionCache 节点
return cache[idx];
}
private boolean allocate(MemoryRegionCache<?> cache, PooledByteBuf buf, int reqCapacity) {if (cache == null) {
// no cache found so just return false here
return false;
}
boolean allocated = cache.allocate(buf, reqCapacity);
if (++ allocations >= freeSweepAllocationThreshold) {
allocations = 0;
trim();}
return allocated;
}
public final boolean allocate(PooledByteBuf<T> buf, int reqCapacity) {
// 找到对应 size 的 MemoryRegionCache 后，用它的 queue 弹出一个 entry
Entry<T> entry = queue.poll();
if (entry == null) {return false;}
// 初始化
initBuf(entry.chunk, entry.handle, buf, reqCapacity);
// 回收 entry 对象
entry.recycle();
// allocations is not thread-safe which is fine as this is only called from the same thread all time.
++ allocations;
return true;
}
protected void initBuf(PoolChunk<T> chunk, long handle, PooledByteBuf<T> buf, int reqCapacity) {chunk.initBufWithSubpage(buf, handle, reqCapacity);
}
private void initBufWithSubpage(PooledByteBuf<T> buf, long handle, int bitmapIdx, int reqCapacity) {
assert bitmapIdx != 0;
int memoryMapIdx = memoryMapIdx(handle);
PoolSubpage<T> subpage = subpages[subpageIdx(memoryMapIdx)];
assert subpage.doNotDestroy;
assert reqCapacity <= subpage.elemSize;
buf.init(
this, handle,
runOffset(memoryMapIdx) + (bitmapIdx & 0x3FFFFFFF) * subpage.elemSize, reqCapacity, subpage.elemSize,
arena.parent.threadCache());
}
void init(PoolChunk<T> chunk, long handle, int offset, int length, int maxLength, PoolThreadCache cache) {
assert handle >= 0;
assert chunk != null;
this.chunk = chunk;
this.handle = handle;
memory = chunk.memory;
this.offset = offset;
this.length = length;
this.maxLength = maxLength;
tmpNioBuf = null;
this.cache = cache;
}
void recycle() {
chunk = null;
handle = -1;
recyclerHandle.recycle(this);
}
public void recycle(Object object) {if (object != value) {throw new IllegalArgumentException("object does not belong to handle");
}
stack.push(this);
}未命中缓存
arena 数据结构
依照内存使用率，把雷同内存使用率的 chunk 归为一个 chunkList，而后 chunkList 之间双向连贯。
每个 chunk 的大小是 16M，分配内存不可能每次申请都调配 16M，所以 chunk 又能够划分为不同大小的 subPage。
page 级别内存调配
private synchronized void allocateNormal(PooledByteBuf<T> buf, int reqCapacity, int normCapacity) {
// 尝试在 chunkList 链表上进行调配
if (q050.allocate(buf, reqCapacity, normCapacity) || q025.allocate(buf, reqCapacity, normCapacity) ||
q000.allocate(buf, reqCapacity, normCapacity) || qInit.allocate(buf, reqCapacity, normCapacity) ||
q075.allocate(buf, reqCapacity, normCapacity)) {
++allocationsNormal;
return;
}
// 以后没有适合的 chunk，就创立一个 chunk
PoolChunk<T> c = newChunk(pageSize, maxOrder, pageShifts, chunkSize);
// 通过 chunk 调配指定大小的一块内存，返回一个 handle
// handle 指向 chunk 内调配的一块间断内存
long handle = c.allocate(normCapacity);
++allocationsNormal;
assert handle > 0;
// 拿到内存后，初始化 PoolByteBuf
c.initBuf(buf, handle, reqCapacity);
qInit.add(c);
}- 现有 chunk 上调配
boolean allocate(PooledByteBuf<T> buf, int reqCapacity, int normCapacity) {if (head == null || normCapacity > maxCapacity) {
// Either this PoolChunkList is empty or the requested capacity is larger then the capacity which can
// be handled by the PoolChunks that are contained in this PoolChunkList.
return false;
}
// 遍历 chunkList，尝试调配
for (PoolChunk<T> cur = head;;) {long handle = cur.allocate(normCapacity);
// handle<0 阐明调配失败，持续遍历
if (handle < 0) {
cur = cur.next;
if (cur == null) {return false;}
} else {
// 调配胜利，初始化 byteBuf
cur.initBuf(buf, handle, reqCapacity);
// 查看以后 chunk 调配后的使用率是否还满足原来的使用率范畴
// 不满足就将它转移到别的 chunkList
if (cur.usage() >= maxUsage) {remove(cur);
nextList.add(cur);
}
return true;
}
}
}- 创立一个 chunk 调配
protected PoolChunk<ByteBuffer> newChunk(int pageSize, int maxOrder, int pageShifts, int chunkSize) {
return new PoolChunk<ByteBuffer>(this, allocateDirect(chunkSize),
pageSize, maxOrder, pageShifts, chunkSize);
}
// 调用 JDK API，分配内存
private static ByteBuffer allocateDirect(int capacity) {return PlatformDependent.useDirectBufferNoCleaner() ?
PlatformDependent.allocateDirectNoCleaner(capacity) : ByteBuffer.allocateDirect(capacity);
}netty 用一个齐全二叉树示意一个 chunk 被调配的状况。
示意形式有点像线段树，树的每个节点代表一段区间，通过这个节点来示意这段区间有没有被应用。
叶子节点 (一个 page) 示意的区间大小为 8k，一个 chunk 也就是根节点的大小是 16M，所以树的高度为 11。
节点示意相应的区间是否被调配
PoolChunk(PoolArena<T> arena, T memory, int pageSize, int maxOrder, int pageShifts, int chunkSize) {
unpooled = false;
this.arena = arena;
this.memory = memory;
this.pageSize = pageSize;
this.pageShifts = pageShifts;
this.maxOrder = maxOrder;
this.chunkSize = chunkSize;
unusable = (byte) (maxOrder + 1);
log2ChunkSize = log2(chunkSize);
subpageOverflowMask = ~(pageSize - 1);
freeBytes = chunkSize;
assert maxOrder < 30 : "maxOrder should be < 30, but is:" + maxOrder;
maxSubpageAllocs = 1 << maxOrder;
// Generate the memory map.
// memoryMap、depthMap 示意第几个节点在树的第几层
memoryMap = new byte[maxSubpageAllocs << 1];
depthMap = new byte[memoryMap.length];
int memoryMapIndex = 1;
// 遍历树的每一层
for (int d = 0; d <= maxOrder; ++ d) { // move down the tree one level at a time
int depth = 1 << d;
// 遍历这一层的每个节点
for (int p = 0; p < depth; ++ p) {
// in each level traverse left to right and set value to the depth of subtree
memoryMap[memoryMapIndex] = (byte) d;
depthMap[memoryMapIndex] = (byte) d;
memoryMapIndex ++;
}
}
subpages = newSubpageArray(maxSubpageAllocs);
}long allocate(int normCapacity) {if ((normCapacity & subpageOverflowMask) != 0) { // >= pageSize
return allocateRun(normCapacity);
} else {return allocateSubpage(normCapacity);
}
}
private long allocateRun(int normCapacity) {
// 算出要调配的内存在树的第几层
int d = maxOrder - (log2(normCapacity) - pageShifts);
int id = allocateNode(d);
if (id < 0) {return id;}
freeBytes -= runLength(id);
return id;
}
// 在算出的层数上进行内存调配
private int allocateNode(int d) {
int id = 1;
int initial = - (1 << d); // has last d bits = 0 and rest all = 1
byte val = value(id);
if (val > d) { // unusable
return -1;
}
while (val < d || (id & initial) == 0) { // id & initial == 1 << d for all ids at depth d, for < d it is 0
id <<= 1;
val = value(id);
if (val > d) {
id ^= 1;
val = value(id);
}
}
byte value = value(id);
assert value == d && (id & initial) == 1 << d : String.format("val = %d, id & initial = %d, d = %d",
value, id & initial, d);
// 标记这个节点已被应用
setValue(id, unusable); // mark as unusable
// 逐层向上标记它的父节点已被应用
updateParentsAlloc(id);
return id;
}初始化 byteBuf
void initBuf(PooledByteBuf<T> buf, long handle, int reqCapacity) {int memoryMapIdx = memoryMapIdx(handle);
int bitmapIdx = bitmapIdx(handle);
if (bitmapIdx == 0) {byte val = value(memoryMapIdx);
assert val == unusable : String.valueOf(val);
buf.init(this, handle, runOffset(memoryMapIdx), reqCapacity, runLength(memoryMapIdx),
arena.parent.threadCache());
} else {initBufWithSubpage(buf, handle, bitmapIdx, reqCapacity);
}
}void init(PoolChunk<T> chunk, long handle, int offset, int length, int maxLength, PoolThreadCache cache) {
assert handle >= 0;
assert chunk != null;
this.chunk = chunk;
this.handle = handle;
memory = chunk.memory;
this.offset = offset;
this.length = length;
this.maxLength = maxLength;
tmpNioBuf = null;
this.cache = cache;
}subPage 级别的内存调配
- 定位到一个 subPage
- 初始化 subPage(在 chunk 中找到一个 page，对这个 page 依照自定义的 subPage 大小进行划分)
- 初始化 ByteBuf
// tableIdx 是间接将申请的内存大小除以 16
tableIdx = tinyIdx(normCapacity);
// 数组，不同下标示意不同大小的 subPage
table = tinySubpagePools;
// 拿到对应大小的的 subPage 的链表头结点
final PoolSubpage<T> head = table[tableIdx];tinySubpagePools 构造和 MemoryRegionCache 的 tiny 数组相似，不同下标代表不同大小的内存。
先通过 allocateNormal 调配
// 与 page 级别不同的是，这里会走到上面的 allocateSubpage
long allocate(int normCapacity) {if ((normCapacity & subpageOverflowMask) != 0) { // >= pageSize
return allocateRun(normCapacity);
} else {return allocateSubpage(normCapacity);
}
}
private long allocateSubpage(int normCapacity) {
// Obtain the head of the PoolSubPage pool that is owned by the PoolArena and synchronize on it.
// This is need as we may add it back and so alter the linked-list structure.
PoolSubpage<T> head = arena.findSubpagePoolHead(normCapacity);
synchronized (head) {// d 间接赋值为 11，在树的最初一层调配(因为最初一次层的大小是一个 page，大于要调配的大小)
int d = maxOrder; // subpages are only be allocated from pages i.e., leaves
int id = allocateNode(d);
if (id < 0) {return id;}
final PoolSubpage<T>[] subpages = this.subpages;
final int pageSize = this.pageSize;
freeBytes -= pageSize;
// subpageIdx: 这个 subPage 在 page 中的地位
int subpageIdx = subpageIdx(id);
PoolSubpage<T> subpage = subpages[subpageIdx];
if (subpage == null) {subpage = new PoolSubpage<T>(head, this, id, runOffset(id), pageSize, normCapacity);
subpages[subpageIdx] = subpage;
} else {subpage.init(head, normCapacity);
}
return subpage.allocate();}
}
PoolSubpage(PoolSubpage<T> head, PoolChunk<T> chunk, int memoryMapIdx, int runOffset, int pageSize, int elemSize) {
this.chunk = chunk;
this.memoryMapIdx = memoryMapIdx;
this.runOffset = runOffset;
this.pageSize = pageSize;
bitmap = new long[pageSize >>> 10]; // pageSize / 16 / 64
init(head, elemSize);
}
void init(PoolSubpage<T> head, int elemSize) {
doNotDestroy = true;
this.elemSize = elemSize;
if (elemSize != 0) {
maxNumElems = numAvail = pageSize / elemSize;
nextAvail = 0;
bitmapLength = maxNumElems >>> 6;
if ((maxNumElems & 63) != 0) {bitmapLength ++;}
// bitmap: 示意 page 中那个 subPage 已被调配
for (int i = 0; i < bitmapLength; i ++) {bitmap[i] = 0;
}
}
addToPool(head);
}
// 将创立好的 subPage 加到 tinySubpagePools 的链表中
private void addToPool(PoolSubpage<T> head) {
assert prev == null && next == null;
prev = head;
next = head.next;
next.prev = this;
head.next = this;
}long allocate() {if (elemSize == 0) {return toHandle(0);
}
if (numAvail == 0 || !doNotDestroy) {return -1;}
final int bitmapIdx = getNextAvail();
int q = bitmapIdx >>> 6;
int r = bitmapIdx & 63;
assert (bitmap[q] >>> r & 1) == 0;
bitmap[q] |= 1L << r;
if (-- numAvail == 0) {removeFromPool();
}
return toHandle(bitmapIdx);
}
private long toHandle(int bitmapIdx) {return 0x4000000000000000L | (long) bitmapIdx << 32 | memoryMapIdx;
}private void initBufWithSubpage(PooledByteBuf<T> buf, long handle, int bitmapIdx, int reqCapacity) {
assert bitmapIdx != 0;
int memoryMapIdx = memoryMapIdx(handle);
PoolSubpage<T> subpage = subpages[subpageIdx(memoryMapIdx)];
assert subpage.doNotDestroy;
assert reqCapacity <= subpage.elemSize;
buf.init(
this, handle,
runOffset(memoryMapIdx) + (bitmapIdx & 0x3FFFFFFF) * subpage.elemSize, reqCapacity, subpage.elemSize,
arena.parent.threadCache());
}ByteBuf 的开释
- 将要开释的内存加到缓存
- 如果退出缓存失败(缓存已满)，就标记该内存未应用
- 将 ByteBuf 放到对象池
private boolean release0(int decrement) {for (;;) {
int refCnt = this.refCnt;
if (refCnt < decrement) {throw new IllegalReferenceCountException(refCnt, -decrement);
}
if (refCntUpdater.compareAndSet(this, refCnt, refCnt - decrement)) {
// 援用计数缩小到 decrement
if (refCnt == decrement) {deallocate();
return true;
}
return false;
}
}
}
protected final void deallocate() {if (handle >= 0) {
final long handle = this.handle;
this.handle = -1;
memory = null;
chunk.arena.free(chunk, handle, maxLength, cache);
recycle();}
}
void free(PoolChunk<T> chunk, long handle, int normCapacity, PoolThreadCache cache) {if (chunk.unpooled) {int size = chunk.chunkSize();
destroyChunk(chunk);
activeBytesHuge.add(-size);
deallocationsHuge.increment();} else {SizeClass sizeClass = sizeClass(normCapacity);
if (cache != null && cache.add(this, chunk, handle, normCapacity, sizeClass)) {
// cached so not free it.
return;
}
freeChunk(chunk, handle, sizeClass);
}
}
boolean add(PoolArena<?> area, PoolChunk chunk, long handle, int normCapacity, SizeClass sizeClass) {MemoryRegionCache<?> cache = cache(area, normCapacity, sizeClass);
if (cache == null) {return false;}
return cache.add(chunk, handle);
}
public final boolean add(PoolChunk<T> chunk, long handle) {Entry<T> entry = newEntry(chunk, handle);
boolean queued = queue.offer(entry);
if (!queued) {
// If it was not possible to cache the chunk, immediately recycle the entry
entry.recycle();}
return queued;
}增加缓存失败
void freeChunk(PoolChunk<T> chunk, long handle, SizeClass sizeClass) {
final boolean destroyChunk;
synchronized (this) {switch (sizeClass) {
case Normal:
++deallocationsNormal;
break;
case Small:
++deallocationsSmall;
break;
case Tiny:
++deallocationsTiny;
break;
default:
throw new Error();}
destroyChunk = !chunk.parent.free(chunk, handle);
}
if (destroyChunk) {
// destroyChunk not need to be called while holding the synchronized lock.
destroyChunk(chunk);
}
}
// 标记内存为未应用
void free(long handle) {int memoryMapIdx = memoryMapIdx(handle);
int bitmapIdx = bitmapIdx(handle);
if (bitmapIdx != 0) { // free a subpage
PoolSubpage<T> subpage = subpages[subpageIdx(memoryMapIdx)];
assert subpage != null && subpage.doNotDestroy;
// Obtain the head of the PoolSubPage pool that is owned by the PoolArena and synchronize on it.
// This is need as we may add it back and so alter the linked-list structure.
PoolSubpage<T> head = arena.findSubpagePoolHead(subpage.elemSize);
synchronized (head) {if (subpage.free(head, bitmapIdx & 0x3FFFFFFF)) {return;}
}
}
freeBytes += runLength(memoryMapIdx);
setValue(memoryMapIdx, depth(memoryMapIdx));
updateParentsFree(memoryMapIdx);
}将 ByteBuf 退出到对象池
private void recycle() {recyclerHandle.recycle(this);
}正文完