heima并发---ConcurrentHashMap系列后续-p6-281和以后
博客：https://www.cnblogs.com/cjsblog/p/10017911.html
博客：https://www.jianshu.com/p/865c813f2726
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put方法：
final V putVal(K key, V value, boolean onlyIfAbsent) {
// 这里面的key和value是不能为空的
if (key == null || value == null) throw new NullPointerException();
// 算出hash值
int hash = spread(key.hashCode());
int binCount = 0;
for (Node[] tab = table;;) {
Node f; int n, i, fh;
if (tab == null || (n = tab.length) == 0)
// 数组为空首先要初始化数组
tab = initTable();
else if ((f = tabAt(tab, i = (n - 1) & hash)) == null) {
// 拿到为空的就设置值
if (casTabAt(tab, i, null,
new Node(hash, key, value, null)))
break; // no lock when adding to empty bin
}
// moved是-1，扩容的
else if ((fh = f.hash) == MOVED)
tab = helpTransfer(tab, f);
else {// 插入的位置不为空的时候 可能是链表 可能是红黑树
V oldVal = null;
synchronized (f) {// 加锁不是分段锁是对f加锁的 就是链表的第一个节点
if (tabAt(tab, i) == f) {// 判断还是不是头节点了 双重校验
if (fh >= 0) {
binCount = 1;// 计数器记录当前位置有几个节点
for (Node e = f;; ++binCount) {
// 遍历链表 替换旧值
K ek;
if (e.hash == hash &&
((ek = e.key) == key ||
(ek != null && key.equals(ek)))) {
oldVal = e.val;
if (!onlyIfAbsent)
e.val = value;
break;
}
Node pred = e;
if ((e = e.next) == null) {// 没有找到加到链表的尾部
pred.next = new Node(hash, key,
value, null);
break;
}
}
}
else if (f instanceof TreeBin) {// 树的添加
Node p;
binCount = 2;
if ((p = ((TreeBin)f).putTreeVal(hash, key,
value)) != null) {
oldVal = p.val;
if (!onlyIfAbsent)
p.val = value;
}
}
}
}
if (binCount != 0) {
if (binCount >= TREEIFY_THRESHOLD)
treeifyBin(tab, i);// 树化
if (oldVal != null)
return oldVal;// 返回旧值
break;
}
}
}
addCount(1L, binCount);
return null;
} 代码拆分：
注意unsafe的方法：
unsafe源码：https://www.cnblogs.com/dennyzhangdd/p/7230012.html
注意指向的关系。
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看下树化的逻辑：
private final void treeifyBin(Node[] tab, int index) {
Node b; int n, sc;
if (tab != null) {
if ((n = tab.length) < MIN_TREEIFY_CAPACITY)
tryPresize(n << 1);
else if ((b = tabAt(tab, index)) != null && b.hash >= 0) {
synchronized (b) {
if (tabAt(tab, index) == b) {// 和hashmap一样还是先改为双向链表
TreeNode hd = null, tl = null;
for (Node e = b; e != null; e = e.next) {
TreeNode p =
new TreeNode(e.hash, e.key, e.val,
null, null);
if ((p.prev = tl) == null)
hd = p;
else
tl.next = p;
tl = p;
}
setTabAt(tab, index, new TreeBin(hd));// 生成红黑树
}
}
}
}
} 注意存的是什么？
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TreeBin就是一个对象，包括树的头节点。
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初始化：
初始化table：https://www.jianshu.com/p/7471f98988bd
/**
* Initializes table, using the size recorded in sizeCtl.
*/
private final Node[] initTable() {
Node[] tab; int sc;
while ((tab = table) == null || tab.length == 0) {
if ((sc = sizeCtl) < 0)// 默认是0 初始化为-1
Thread.yield(); // lost initialization race; just spin
else if (U.compareAndSwapInt(this, SIZECTL, sc, -1)) {
try {
if ((tab = table) == null || tab.length == 0) {
int n = (sc > 0) ? sc : DEFAULT_CAPACITY;
@SuppressWarnings("unchecked")
Node[] nt = (Node[])new Node[n];
table = tab = nt;
sc = n - (n >>> 2);
}
} finally {
sizeCtl = sc;
}
break;
}
}
return tab;
}
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扩容：
private final void addCount(long x, int check) {
CounterCell[] as; long b, s;
// 完成baseCount++的操作
if ((as = counterCells) != null ||
// baseCOunt增加失败
!U.compareAndSwapLong(this, BASECOUNT, b = baseCount, s = b + x)) {
CounterCell a; long v; int m;
boolean uncontended = true;
if (as == null || (m = as.length - 1) < 0 ||
(a = as[ThreadLocalRandom.getProbe() & m]) == null ||
!(uncontended =
// 失败
U.compareAndSwapLong(a, CELLVALUE, v = a.value, v + x))) {
fullAddCount(x, uncontended);// 这个包括了很多东西
return;
}
if (check <= 1)
return;
s = sumCount();//
}
if (check >= 0) {
Node[] tab, nt; int n, sc;
while (s >= (long)(sc = sizeCtl) && (tab = table) != null &&
(n = tab.length) < MAXIMUM_CAPACITY) {
int rs = resizeStamp(n);
if (sc < 0) {
if ((sc >>> RESIZE_STAMP_SHIFT) != rs || sc == rs + 1 ||
sc == rs + MAX_RESIZERS || (nt = nextTable) == null ||
transferIndex <= 0)
break;
if (U.compareAndSwapInt(this, SIZECTL, sc, sc + 1))
transfer(tab, nt);
}
else if (U.compareAndSwapInt(this, SIZECTL, sc,
(rs << RESIZE_STAMP_SHIFT) + 2))
transfer(tab, null);
s = sumCount();
}
}
}
counterCell的思路：
我们做下实验，看下sum就明白了：
cellCount：https://blog.csdn.net/chenssy/article/details/73521950，https://www.sohu.com/a/254192521_355142
https://www.jianshu.com/p/749d1b8db066
看下
// See LongAdder version for explanation
private final void fullAddCount(long x, boolean wasUncontended) {
int h;
if ((h = ThreadLocalRandom.getProbe()) == 0) {
ThreadLocalRandom.localInit(); // force initialization
h = ThreadLocalRandom.getProbe();
wasUncontended = true;
}
boolean collide = false; // True if last slot nonempty
for (;;) {
CounterCell[] as; CounterCell a; int n; long v;
if ((as = counterCells) != null && (n = as.length) > 0) {
if ((a = as[(n - 1) & h]) == null) {
if (cellsBusy == 0) { // Try to attach new Cell
CounterCell r = new CounterCell(x); // Optimistic create
if (cellsBusy == 0 &&
U.compareAndSwapInt(this, CELLSBUSY, 0, 1)) {
boolean created = false;
try { // Recheck under lock
CounterCell[] rs; int m, j;
if ((rs = counterCells) != null &&
(m = rs.length) > 0 &&
rs[j = (m - 1) & h] == null) {
rs[j] = r;
created = true;
}
} finally {
cellsBusy = 0;
}
if (created)
break;
continue; // Slot is now non-empty
}
}
collide = false;
}
else if (!wasUncontended) // CAS already known to fail
wasUncontended = true; // Continue after rehash
else if (U.compareAndSwapLong(a, CELLVALUE, v = a.value, v + x))
break;
else if (counterCells != as || n >= NCPU)
collide = false; // At max size or stale
else if (!collide)
collide = true;
else if (cellsBusy == 0 &&
U.compareAndSwapInt(this, CELLSBUSY, 0, 1)) {
try {
if (counterCells == as) {// Expand table unless stale
CounterCell[] rs = new CounterCell[n << 1];
for (int i = 0; i < n; ++i)
rs[i] = as[i];
counterCells = rs;
}
} finally {
cellsBusy = 0;
}
collide = false;
continue; // Retry with expanded table
}
h = ThreadLocalRandom.advanceProbe(h);
}
else if (cellsBusy == 0 && counterCells == as &&
U.compareAndSwapInt(this, CELLSBUSY, 0, 1)) {
boolean init = false;
try { // Initialize table
if (counterCells == as) {
CounterCell[] rs = new CounterCell[2];
rs[h & 1] = new CounterCell(x);
counterCells = rs;
init = true;
}
} finally {
cellsBusy = 0;
}
if (init)
break;
}
else if (U.compareAndSwapLong(this, BASECOUNT, v = baseCount, v + x))
break; // Fall back on using base
}
}
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什么时候扩容：https://blog.csdn.net/varyall/article/details/81277296
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