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in Technique[技术] by (71.8m points)

ConcurrentHashMap类型的成员变量,为何在业务方法中还要加锁?

nacos源码中对tasks加锁,不懂为何要这样使用。

public class NacosDelayTaskExecuteEngine extends AbstractNacosTaskExecuteEngine<AbstractDelayTask> {
    
    private final ScheduledExecutorService processingExecutor;
    
    protected final ConcurrentHashMap<Object, AbstractDelayTask> tasks;
    
    @Override
    public boolean isEmpty() {
        lock.lock();
        try {
            return tasks.isEmpty();
        } finally {
            lock.unlock();
        }
    }
    
    
    }

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ConcurrentHashMap使用了分段锁提升并发性能,但在size和isEmpty时,并不能保证并发下的准确性。算是性能和准确性的一个折中妥协吧


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