AtomicInteger
每个 AtomicInteger 对象中都包含了 整数 value, 所以，该类利用 valueOffset 表示当前 value 在对象中内存首地址的偏移量
getAndIncrement
返回旧值， 然后自增1
/**
* Atomically increments by one the current value.
*
* @return the previous value
*/
public final int getAndIncrement() {
return unsafe.getAndAddInt(this, valueOffset, 1);
}
/*
var1 当前对象
var2 偏移量
var4
该方法 首先利用 var5 保存 expectValue
var5 + var4 == newValue
*/
public final int getAndAddInt(Object var1, long var2, int var4) {
int var5;
do {
var5 = this.getIntVolatile(var1, var2);
} while(!this.compareAndSwapInt(var1, var2, var5, var5 + var4));
return var5;
}
getAndDecrement
先获取值，再减一
/**
* Atomically decrements by one the current value.
*
* @return the previous value
*/
public final int getAndDecrement() {
return unsafe.getAndAddInt(this, valueOffset, -1);
}
getAndAdd
这个比较有意思的是，我先获取旧值，然后 增加 delta
/**
* Atomically adds the given value to the current value.
*
* @param delta the value to add
* @return the previous value
*/
public final int getAndAdd(int delta) {
return unsafe.getAndAddInt(this, valueOffset, delta);
}
incrementAndGet
因为 getAdnAddInt 是获取 旧值，然后自增1，但是，该方法希望首先自增1，然后获取新值
/**
* Atomically increments by one the current value.
*
* @return the updated value
*/
public final int incrementAndGet() {
return unsafe.getAndAddInt(this, valueOffset, 1) + 1;
}
decrementAndGet
/**
* Atomically decrements by one the current value.
*
* @return the updated value
*/
public final int decrementAndGet() {
return unsafe.getAndAddInt(this, valueOffset, -1) - 1;
}
addAndGet
该方法也是首先自增，然后获取
/**
* Atomically adds the given value to the current value.
*
* @param delta the value to add
* @return the updated value
*/
public final int addAndGet(int delta) {
return unsafe.getAndAddInt(this, valueOffset, delta) + delta;
}
compareAndSet
expect value
update newValue
这个只是返回是否修改成功
/**
* Atomically sets the value to the given updated value
* if the current value {@code ==} the expected value.
*
* @param expect the expected value
* @param update the new value
* @return {@code true} if successful. False return indicates that
* the actual value was not equal to the expected value.
*/
public final boolean compareAndSet(int expect, int update) {
return unsafe.compareAndSwapInt(this, valueOffset, expect, update);
}
getAndSet
这个方法修改 值，返回的是旧值
/**
* Atomically sets to the given value and returns the old value.
*
* @param newValue the new value
* @return the previous value
*/
public final int getAndSet(int newValue) {
return unsafe.getAndSetInt(this, valueOffset, newValue);
}
