Unsafe类存在于sun.misc包中,其内部方法操作可以像C的指针一样直接操作内存,单从名称看来就可以知道该类是非安全的,毕竟Unsafe拥有着类似于C的指针操作,因此总是不应该首先使用Unsafe类,Java官方也不建议直接使用的Unsafe类,据说Oracle正在计划从Java 9中去掉Unsafe类,但我们还是很有必要了解该类,因为Java中CAS操作的...
所以我们在编写程序时如果没有什么特殊要求不应该考虑使用它,并且Java官方也不推荐使用(Unsafe也不对外提供构造函数),而且Oracle官方当初也打算在Java9中去掉Unsafe类。但是由于Java并发包中大量使用了该类,所以Oracle最终在Java并没有移除掉Unsafe类,只是做了相对于的优化与维护,而且除开并发包之外,类似于Netty等框架也...
直到设置成功方能退出循环,返回旧值publicfinalintgetAndAddInt(Object o,longoffset,intdelta){intv;do{//获取内存中最新值v=getIntVolatile(o,offset);//通过CAS操作}while(!compareAndSwapInt(o,offset,v,v+delta));returnv;}//1.8新增,方法作用同上,只不过这里操作的long类型数据publicfinallonggetAndAdd...
Modifier and Type Method Description E accumulateAndGet(int i, E x, BinaryOperator<E> accumulatorFunction) Atomically updates the element at index i with the results of applying the given function to the current and given values, returning the updated value. boolean compareAndSet...
As you saw in the preceding section, you cannot safely read a field from multiple threads unless you use locks or thevolatilemodifier. There is one other situation in which it is safe to access a shared field: when it is declaredfinal. Consider ...
Modifier and Type Method Description boolean attemptMark(V expectedReference, boolean newMark) Atomically sets the value of the mark to the given update value if the current reference is == to the expected reference. boolean compareAndSet(V expectedReference, V newReference, boolean expectedMark, ...
java.lang.RuntimeException:java.lang.IllegalAccessException:Classxxx.AtomicIntegerFieldUpdateTestcan not access a member ofclassxxx.AtomicIntegerFieldUpdateTest$Userwithmodifiers"private"java.lang.ExceptionInInitializerErrorCausedby:java.lang.IllegalArgumentException:Mustbevolatiletype//源码:if(!Modifier.isVolat...
weakCompareAndSet( )方法和compareAndSet( )类似,都是conditional modifier方法。这2个方法接受2个参数,一个是期望数据(expected),一个是新数据(new);如果atomic里面的数据和期望数据一 致,则将新数据设定给atomic的数据,返回true,表明成功;否则就不设定,并返回false。JSR规范中说:以原子方式读取和有条件地写入变...
类路径:java.util.concurrent.atomic.AtomicBoolean 保证了boolean操作的原子性 // 创建Unsafe类的实例 privatestaticfinalUnsafeunsafe=Unsafe.getUnsafe(); // 变量value的偏移量, 具体赋值是在下面的静态代码块中中进行的 privatestaticfinallongvalueOffset; ...
classA{privatestaticvolatileintvalue=0;privatestaticfinalAtomicIntegerFieldUpdaterupdater=AtomicIntegerFieldUpdater.newUpdater((A.class),"value");// warning: Field 'value' has 'static' modifier} classB{privatestaticfinalAtomicIntegerFieldUpdaterupdater=AtomicIntegerFieldUpdater.newUpdater(B.class,"value");// ...