Java Multithreading: "Juc Atomic class" 04 Atomicreference Atomic class

Atomicreference Introduction and Functions List

Atomicreference is a function of atomic manipulation of "objects".

atomicreference Function List

// Create a new AtomicReference with null initial value.
AtomicReference ()
// Create a new AtomicReference with the given initial value.
AtomicReference (V initialValue)
    
// If the current value == the expected value, then atomically set the value to the given update value.
boolean compareAndSet (V expect, V update)
// Get the current value.
V get ()
// Set to the given value atomically and return the old value.
V getAndSet (V newValue)
// Finally set to the given value.
void lazySet (V newValue)
// Set to the given value.
void set (V newValue)
// Return the string representation of the current value.
String toString ()
// If the current value == the expected value, then atomically set the value to the given update value.
boolean weakCompareAndSet (V expect, V update)
AtomicReference source code analysis (based on JDK1.7.0_40)

The source code of AtomicReference.java in JDK1.7.0_40 is as follows:

public class AtomicReference <V> implements java.io.Serializable {
    private static final long serialVersionUID = -1848883965231344442L;
    
    // Get Unsafe object, the role of Unsafe is to provide CAS operation
    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);}
    }
    
    // volatile type
    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);
    }
    
    public final V getAndSet (V newValue) {
        while (true) {
            V x = get ();
            if (compareAndSet (x, newValue))
                return x;
        }
    }
    
    public String toString () {
        return String.valueOf (get ());
    }
}