[JUC supplementary] atomic class, unsafe

reference：https://zhuanlan.zhihu.com/p/115345089
atomic Class provides many classes , These classes perform atomic operations on different data types

example

Source code analysis

The bottom is unsafe Class cas operation , and Unsafe The bottom layer is actually calling C Code （native Keyword modification ）,C Code calls assembly , Finally, a CPU Instructions cmpxchg, To complete the operation . That's why CAS It's atomic , because It's a CPU Instructions , Will not be interrupted .

Unsafe

Now that it's up there unsafe Here to learn more
obtain unsafe：
Because its constructor is private, it cannot new

Earlier versions use reflection to get the internally created theUnsafe：

    Field f = Unsafe.class.getDeclaredField("theUnsafe");
    f.setAccessible(true);// Set up private by  public
    Unsafe unsafe = (Unsafe) f.get(null);

The latest version is more open and offers get Go straight back to

except cas What other operations are relatively low-level ？

Locksupport Of park And unpark stay unsafe The underlying implementation of

Operate on memory , It's a memory level operation , You can specify the memory address and release , Very low level