通过访问器检索的实例成员的线程安全

Question

Class A 's methods are accessed by two threads. One thread updates it. The other retrieves its member.

public class A {
    private V v;

    public V getV() {
        return v;
    }

    public V updateV(A a, B b, Cc) {
        //complex logic updating V
    }
}

How can I make V thread safe?

Answer 1

The easiest way to make V thread safe is to make it immutable (by making final all its non static fields) then in A you simply affect a new instance of V in updateV as next:

public class A {
    private V v;

    public synchronized V getV() {
        return v;
    }

    public synchronized V updateV(A a, B b, Cc) {
        //complex logic updating V
        this.v = new V(...);
        return v;
    }
}

As you can see to make A thread safe I simply added the keyword synchronized to the getter and the setter to prevent concurrent read and write but if it is not needed in your case you can sill make v volatile as next:

public class A {
    private volatile V v;

    public V getV() {
        return v;
    }

    public V updateV(A a, B b, Cc) {
        //complex logic updating V
        this.v = new V(...);
        return v;
    }
}