Java源码解析ConcurrentHashMap的初始化

private final Node<K,V>[] initTable() {
    Node<K,V>[] tab; int sc;
    while ((tab = table) == null || tab.length == 0) { // 第一次检查
      if ((sc = sizeCtl) < 0)
        Thread.yield(); // lost initialization race; just spin
      else if (U.compareAndSwapInt(this, SIZECTL, sc, -1)) {
        try {
          if ((tab = table) == null || tab.length == 0) {// 第二次检查
            int n = (sc > 0) ? sc : DEFAULT_CAPACITY;
            @SuppressWarnings("unchecked")
            Node<K,V>[] nt = (Node<K,V>[])new Node<?,?>[n];
            table = tab = nt;
            sc = n - (n >>> 2);
          }
        } finally {
          sizeCtl = sc;
        }
        break;
      }
    }
    return tab;
  }