我正在创建一个同时执行方法的接口,同时抽象出同步细节(在需要时交换分布式实现).我已经创建了一个单独的jvm实现,它允许将字符串作为互斥体存储在映射中,以确保使用一个引用,即使传入不同引用的字符串.并发似乎工作正常,但我是惊讶地看到测试表明参考计数从未减少.我假设使用WeakValues()就足以防止内存泄漏,但似乎并非如此.任何人都可以指出可能导致这种泄漏的原因吗？

public class SynchronousMethodExecutorSynchronizedImpl implements ISynchronousMethodExecutor {

// mutex map to provide string references
final Map<String, String> mutexMap = new MapMaker()
    .weakValues()
    .makeComputingMap(
        new Function<String, String>() {
        @Override
        public String apply(String id) {
            return id;
        }
    });

@Override
public Object doSynchronousMethod(String domain, String id, ISynchronousMethod synchronousMethod) {
    synchronized(mutexMap.get(domain + "." + id))
    {
        return synchronousMethod.execute();
    } 
}

}

这是在最后一个断言失败的测试：

public class SynchronousMethodExecutorSynchronizedImplTest extends TestCase {
int counter;
SynchronousMethodExecutorSynchronizedImpl methodExecutor;

@Override
public void before() throws Exception {
    super.before();

    methodExecutor = new SynchronousMethodExecutorSynchronizedImpl();
}

@Test
public void concurrentExecute() throws InterruptedException {
    assertEquals(0, counter);

    for(int i=0; i<1000; i++)
        getConcurrentExecutorThread().start();

    // wait for threads to complete
    Thread.sleep(1000);

    assertEquals(1, methodExecutor.mutexMap.size());

    try
    { 
        final List<long[]> infiniteList = new LinkedList<long[]>(); 

       for(long i = Long.MIN_VALUE; i < Long.MAX_VALUE; i++)
            infiniteList.add(new long[102400]); 

        fail("An OutOfMemoryError should be thrown");
    } 
    catch(OutOfMemoryError e)
    { 

    }

    assertEquals(2000, counter);
    assertEquals(0, methodExecutor.mutexMap.size());
}

// synchronous method
private ISynchronousMethod method = new ISynchronousMethod() {
    @Override
    public Object execute() {
        counter++;  
        return null;
    }
};

/**
 * Executes a line of code.
 * 
 * @return Thread
 */
private Thread getConcurrentExecutorThread() {
    return new Thread() {
        @Override
        public void run() {
            methodExecutor.doSynchronousMethod("TEST", "1", method);
            try
            {
                Thread.sleep(500);
            }
            catch (InterruptedException e)
            {

            }
            methodExecutor.doSynchronousMethod("TEST", new String("1"), method);        
        }

    };
}

}

最后一个断言是打破测试的原因：
assertEquals(0,methodExecutor.mutexMap.size());

解决方法:

您将存储与键和值完全相同的String对象.关键是对对象的强烈引用,只要存在对它的强引用,对它的弱引用就没有意义了.弱可达(here)的定义指出：

An object is weakly reachable if it is neither strongly nor softly reachable but can be reached by traversing a weak reference.

顺便说一句,即使有了这个纠正,我也不认为你可以假设地图最后总是空的.它可能会接近空洞,但我认为可以说是关于它的所有内容.