番石榴库:Iterators.cycle()线程安全吗? [英] guava-libraries: is Iterators.cycle() thread-safe?

问题描述

假设我有以下课程:

public class Foo {  

    private List<Integer> list = Lists.newArrayList(1, 2, 3, 4, 5);
    private Iterator<Integer> iterator = Iterators.cycle(list);  

    public void bar(){  
        Integer value = iterator.next();  
        doSomethingWithAnInteger(value);
    }  
}  

如果两个线程同时访问Foo的实例，则我需要每个线程从iterator.next()获得不同的值.是否必须使bar()方法同步?还是可以保证iterator.next()是线程安全的?

If an instance of Foo is acessed simultaneously by two threads, I need that each thread gets a different value from iterator.next(). Does the bar() method have to be made synchronized? Or is iterator.next() guaranteed to be thread-safe?

在此示例中，我使用ArrayList作为基础Iterable.循环迭代器的线程安全性是否取决于特定的可迭代实现?

In this example, I am using an ArrayList as the underlying Iterable. Does the thread-safety of the cyclic iterator depend on the specific iterable implementation?

谢谢.

推荐答案

除非有相关说明，否则Guava中几乎没有任何东西可以保证线程安全.

Pretty much nothing in Guava is guaranteed to be thread safe unless documented as such.

您不必同步整个bar方法，但应将对iterator.next()的调用包装在一个同步块中.例如:

You do not have to synchronize the entire bar method, but you should wrap the call to iterator.next() in a synchronized block. eg:

public void bar(){  
    Integer value;
    synchronized (iterator) {
        value = iterator.next();  
    }
    doSomethingWithAnInteger(value);
}  

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