To find entry in the HashMap RI performs: 1) Check that entry.hash==key.hashCode() (entry - hash map entry) 2) Check that entry.key == key or (key!=null && key.eqauls(entry.key))
hm.get(proxyInstance); returns !=null object because entry.key == key in the 2) and equals doesn't perform. Oleg On Wed, Jul 8, 2009 at 8:34 AM, Regis<xu.re...@gmail.com> wrote: > Jim Yu wrote: >> >> 2009/6/18 Regis <xu.re...@gmail.com> >> >>> Jim Yu wrote: >>> >>>> 2009/6/18 Regis <xu.re...@gmail.com> >>>> >>>> Jim Yu wrote: >>>>> >>>>> Hi all, >>>>>> >>>>>> There is an interesting edge case in HashMap. If we use a proxy object >>>>>> as >>>>>> the key to put something into HashMap, we will fail to retrieve the >>>>>> value >>>>>> by >>>>>> using that key. But RI works well for this case. Here is a test case >>>>>> below >>>>>> to present the problem. I found the root cause of the failure for our >>>>>> HashMap is that proxyInstance.equals(proxyInstance) returns false >>>>>> which >>>>>> sounds strange but appears work correctly as both Harmony and RI >>>>>> behave >>>>>> so. >>>>>> >>>>>> It's very interesting behaviors, seems like RI did it intended, are >>>>> >>>>> there >>>>> any cases we need proxyInstance.equals(proxyInstance) return false? >>>>> >>>> >>>> I think it is reasonable to return false here since spec mentioned for >>>> proxy >>>> instance that "An invocation of the hashCode, equals, or toString >>>> methods >>>> declared in java.lang.Object on a proxy instance will be encoded and >>>> dispatched to the invocation handler's invoke method" So the meaning of >>>> equals method seems has been changed by the invoke here: ) >>>> >>>> >>>>> I suspect RI has made some special approaches to match the key when >>>>> the >>>>> >>>>>> key >>>>>> is a proxy object. So I would be inclined to follow RI's behavior in >>>>>> this >>>>>> case. Any thoughts here? >>>>>> >>>>>> I think if proxyInstance.equals(proxyInstance) return false is >>>>> >>>>> reasonable, >>>>> we should do some tricks to make HashMap work with Proxy. And does >>>>> Proxy >>>>> object work well with other collections which used equals to retrieve >>>>> object >>>>> from collection? >>>>> >>>>> >>>> Agree. I have made a patch to do the trick so as to follow RI's >>>> behavior. >>>> >>> The patch looks good for me, applied at r786015, please verify. >> >> >> Verified at r786379. Thanks, Regis. >> >>> >>> >>>> >>>>> I have raised a JIRA at >>>>>> >>>>>> https://issues.apache.org/jira/browse/HARMONY-6237for this issue. >>>>>> >>>>>> >>>>>> public interface MockInterface { >>>>>> public String mockMethod(); >>>>>> } >>>>>> >>>>>> public class MockClass implements MockInterface { >>>>>> public String mockMethod() { >>>>>> return "This is a mock class."; >>>>>> } >>>>>> } >>>>>> >>>>>> import java.lang.reflect.InvocationHandler; >>>>>> import java.lang.reflect.Method; >>>>>> import java.lang.reflect.Proxy; >>>>>> import java.util.HashMap; >>>>>> import java.util.Map; >>>>>> >>>>>> public class TestProxy implements InvocationHandler { >>>>>> >>>>>> Object obj; >>>>>> >>>>>> public TestProxy(Object o) { >>>>>> obj = o; >>>>>> } >>>>>> >>>>>> public Object invoke(Object proxy, Method m, Object[] args) >>>>>> throws Throwable { >>>>>> >>>>>> Object result = null; >>>>>> >>>>>> try { >>>>>> >>>>>> result = m.invoke(obj, args); >>>>>> >>>>>> } catch (Exception e) { >>>>>> e.printStackTrace(); >>>>>> } finally { >>>>>> } >>>>>> return result; >>>>>> } >>>>>> >>>>>> public static void main(String[] argv) throws Exception { >>>>>> >>>>>> MockInterface proxyInstance = (MockInterface) >>>>>> Proxy.newProxyInstance( >>>>>> MockInterface.class.getClassLoader(), >>>>>> new Class[] { MockInterface.class }, new TestProxy( >>>>>> new MockClass())); >>>>>> >>>>>> Map hm = new HashMap(); >>>>>> >>>>>> hm.put(proxyInstance, "Value"); >>>>>> >>>>>> Object o = hm.get(proxyInstance); >>>>>> >>>>>> System.out.println("Value got for proxy object key:" + o); >>>>>> >>>>>> System.out.println(proxyInstance.equals(proxyInstance)); >>>>>> >>>>>> } >>>>>> } >>>>>> >>>>>> Output >>>>>> Harmony: >>>>>> Value got for proxy object key:null >>>>>> false >>>>>> >>>>>> RI: >>>>>> Value got for proxy object key:Value >>>>>> false >>>>>> >>>>>> >>>>>> -- >>>>> >>>>> Best Regards, >>>>> Regis. >>>>> >>>>> >>>> >>>> >>> -- >>> Best Regards, >>> Regis. >>> >> >> >> > > I found this patch involve serious performance regression. Because > Proxy.isProxyClass() synchronized on a instance "proxyCache", which is a > static field of Proxy, so all HashMap.get() will contend for this lock. So > is there other way to test whether a class is Proxy class or > Proxy.isProxyClass() could avoid to use lock of static field? > > > -- > Best Regards, > Regis. >
