非空类成员字段的双重检查锁定

double-checked locking 成语 Java null 如果是这样,则获取具有该字段的类的锁:

// Double-check idiom for lazy initialization of instance fields
// See Pascal Thivent's original answer <https://stackoverflow.com/a/3580658/1391325>
private volatile FieldType field;

FieldType getField() {
    FieldType result = field;
    if (result == null) { // First check (no locking)
        synchronized(this) {
            result = field;
            if (result == null) { // Second check (with locking)
                field = result = computeFieldValue();
            }
        }
    }
    return result;
}

field null object “延迟替换为“非空对象”的值),可以在 this synchronized(field) ?

实例

我有一个很大的 HugeObject Reference<HugeObject> Reference<HugeObject> field = new SoftReference<>(null) 这 因此,使用不影响 领域 领域 。那么是否可以简单地在 此初始“空对象” 或 已经实例化的“非空对象”,或者这会导致微妙的、不想要的并发影响吗?见以下代码:

private volatile Reference<HugeObject> field = new SoftReference<>(null);

HugeObject getField() {
    HugeObject result = field.get();
    if (result == null) {
        synchronized(field) {
            result = field.get();
            if (result == null) {
                result = computeFieldValue();
                field = new SoftReference<>(result);
            }
        }
    }
    return result;
}