在上一篇博客 并发编程--原子类AotmicInteger中我们已经简单介绍了一下AtomicInteger相关的知识，简单来说AtomicLong的实现原理与AtomicInteger是相同的，用volatile来修饰变量value和使用sun.misc.Unsafe来完成对value的原子操作。
AtomicBoolean的实现机制还是比较简单的，通过判断用volatile修改的value与1和0之间的关系来返回true和false，使用sun.misc.Unsafe来完成对value的原子操作
AtomicReference的实现机制就是通过sun.misc.Unsafe来对对象引用进行原子操作。
源码如下：
public class AtomicLong extends Number implements java.io.Serializable {
private static final long serialVersionUID = 1927816293512124184L;
private static final Unsafe unsafe = Unsafe.getUnsafe();
private static final long valueOffset;
static final boolean VM_SUPPORTS_LONG_CAS = VMSupportsCS8();
private static native boolean VMSupportsCS8();
static {
try {
valueOffset = unsafe.objectFieldOffset
(AtomicLong.class.getDeclaredField("value"));
} catch (Exception ex) { throw new Error(ex); }
}
private volatile long value;
public AtomicLong(long initialValue) {
value = initialValue;
}
public AtomicLong() {
}
public final long get() {
return value;
}
public final void set(long newValue) {
value = newValue;
}
public final void lazySet(long newValue) {
unsafe.putOrderedLong(this, valueOffset, newValue);
}
public final long getAndSet(long newValue) {
return unsafe.getAndSetLong(this, valueOffset, newValue);
}
public final boolean compareAndSet(long expect, long update) {
return unsafe.compareAndSwapLong(this, valueOffset, expect, update);
}
public final boolean weakCompareAndSet(long expect, long update) {
return unsafe.compareAndSwapLong(this, valueOffset, expect, update);
}
public final long getAndIncrement() {
return unsafe.getAndAddLong(this, valueOffset, 1L);
}
public final long getAndDecrement() {
return unsafe.getAndAddLong(this, valueOffset, -1L);
}
public final long getAndAdd(long delta) {
return unsafe.getAndAddLong(this, valueOffset, delta);
}
public final long incrementAndGet() {
return unsafe.getAndAddLong(this, valueOffset, 1L) + 1L;
}
public final long decrementAndGet() {
return unsafe.getAndAddLong(this, valueOffset, -1L) - 1L;
}
public final long addAndGet(long delta) {
return unsafe.getAndAddLong(this, valueOffset, delta) + delta;
}
public final long getAndUpdate(LongUnaryOperator updateFunction) {
long prev, next;
do {
prev = get();
next = updateFunction.applyAsLong(prev);
} while (!compareAndSet(prev, next));
return prev;
}
public final long updateAndGet(LongUnaryOperator updateFunction) {
long prev, next;
do {
prev = get();
next = updateFunction.applyAsLong(prev);
} while (!compareAndSet(prev, next));
return next;
}
public final long getAndAccumulate(long x,
LongBinaryOperator accumulatorFunction) {
long prev, next;
do {
prev = get();
next = accumulatorFunction.applyAsLong(prev, x);
} while (!compareAndSet(prev, next));
return prev;
}
public final long accumulateAndGet(long x,
LongBinaryOperator accumulatorFunction) {
long prev, next;
do {
prev = get();
next = accumulatorFunction.applyAsLong(prev, x);
} while (!compareAndSet(prev, next));
return next;
}
public String toString() {
return Long.toString(get());
}
public int intValue() {
return (int)get();
}
public long longValue() {
return get();
}
public float floatValue() {
return (float)get();
}
public double doubleValue() {
return (double)get();
}
}
AtomicBoolean的源码：
public class AtomicBoolean implements java.io.Serializable {
private static final long serialVersionUID = 4654671469794556979L;
private static final Unsafe unsafe = Unsafe.getUnsafe();
private static final long valueOffset;
static {
try {
valueOffset = unsafe.objectFieldOffset
(AtomicBoolean.class.getDeclaredField("value"));
} catch (Exception ex) { throw new Error(ex); }
}
private volatile int value;
public AtomicBoolean(boolean initialValue) {
value = initialValue ? 1 : 0;
}
public AtomicBoolean() {
}
public final boolean get() {
return value != 0;
}
public final boolean compareAndSet(boolean expect, boolean update) {
int e = expect ? 1 : 0;
int u = update ? 1 : 0;
return unsafe.compareAndSwapInt(this, valueOffset, e, u);
}
public boolean weakCompareAndSet(boolean expect, boolean update) {
int e = expect ? 1 : 0;
int u = update ? 1 : 0;
return unsafe.compareAndSwapInt(this, valueOffset, e, u);
}
public final void set(boolean newValue) {
value = newValue ? 1 : 0;
}
public final void lazySet(boolean newValue) {
int v = newValue ? 1 : 0;
unsafe.putOrderedInt(this, valueOffset, v);
}
public final boolean getAndSet(boolean newValue) {
boolean prev;
do {
prev = get();
} while (!compareAndSet(prev, newValue));
return prev;
}
public String toString() {
return Boolean.toString(get());
}
}
AtomicReference源码：
public class AtomicReference<V> implements java.io.Serializable {
private static final long serialVersionUID = -1848883965231344442L;
private static final Unsafe unsafe = Unsafe.getUnsafe();
private static final long valueOffset;
static {
try {
valueOffset = unsafe.objectFieldOffset
(AtomicReference.class.getDeclaredField("value"));
} catch (Exception ex) { throw new Error(ex); }
}
private volatile V value;
public AtomicReference(V initialValue) {
value = initialValue;
}
public AtomicReference() {
}
public final V get() {
return value;
}
public final void set(V newValue) {
value = newValue;
}
public final void lazySet(V newValue) {
unsafe.putOrderedObject(this, valueOffset, newValue);
}
public final boolean compareAndSet(V expect, V update) {
return unsafe.compareAndSwapObject(this, valueOffset, expect, update);
}
public final boolean weakCompareAndSet(V expect, V update) {
return unsafe.compareAndSwapObject(this, valueOffset, expect, update);
}
@SuppressWarnings("unchecked")
public final V getAndSet(V newValue) {
return (V)unsafe.getAndSetObject(this, valueOffset, newValue);
}
public final V getAndUpdate(UnaryOperator<V> updateFunction) {
V prev, next;
do {
prev = get();
next = updateFunction.apply(prev);
} while (!compareAndSet(prev, next));
return prev;
}
public final V updateAndGet(UnaryOperator<V> updateFunction) {
V prev, next;
do {
prev = get();
next = updateFunction.apply(prev);
} while (!compareAndSet(prev, next));
return next;
}
public final V getAndAccumulate(V x,
BinaryOperator<V> accumulatorFunction) {
V prev, next;
do {
prev = get();
next = accumulatorFunction.apply(prev, x);
} while (!compareAndSet(prev, next));
return prev;
}
public final V accumulateAndGet(V x,
BinaryOperator<V> accumulatorFunction) {
V prev, next;
do {
prev = get();
next = accumulatorFunction.apply(prev, x);
} while (!compareAndSet(prev, next));
return next;
}
public String toString() {
return String.valueOf(get());
}
}
