<!-- If you need to report a security issue please visit https://github.com/apache/dubbo/security/policy -->

ExtensionLoader cannot be resumed after interruption.

```
java.lang.InterruptedException
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1302)
  at java.util.concurrent.CountDownLatch.await(CountDownLatch.java:231)
  at org.apache.dubbo.common.utils.ClassLoaderResourceLoader.loadResources(ClassLoaderResourceLoader.java:55)
  at org.apache.dubbo.common.extension.ExtensionLoader.loadDirectory(ExtensionLoader.java:1005)
  at org.apache.dubbo.common.extension.ExtensionLoader.loadDirectory(ExtensionLoader.java:943)
  at org.apache.dubbo.common.extension.ExtensionLoader.loadExtensionClasses(ExtensionLoader.java:931)
  at org.apache.dubbo.common.extension.ExtensionLoader.getExtensionClasses(ExtensionLoader.java:913)
  at org.apache.dubbo.common.extension.ExtensionLoader.createExtension(ExtensionLoader.java:752)
  at org.apache.dubbo.common.extension.ExtensionLoader.getExtension(ExtensionLoader.java:548)
  at org.apache.dubbo.common.extension.ExtensionLoader.getExtension(ExtensionLoader.java:523)
  at org.apache.dubbo.rpc.protocol.injvm.InjvmInvoker.<init>(InjvmInvoker.java:74)
```
return null;
        }
        return getExtension(cachedDefaultName);
    }
    public boolean hasExtension(String name) {
        checkDestroyed();
        if (StringUtils.isEmpty(name)) {
            throw new IllegalArgumentException("Extension name == null");
        }
        Class<?> c = this.getExtensionClass(name);
        return c != null;
    }
    public Set<String> getSupportedExtensions() {
        checkDestroyed();
        Map<String, Class<?>> classes = getExtensionClasses();
        return Collections.unmodifiableSet(new TreeSet<>(classes.keySet()));
    }
    public Set<T> getSupportedExtensionInstances() {
        checkDestroyed();
        List<T> instances = new LinkedList<>();
        Set<String> supportedExtensions = getSupportedExtensions();
        if (CollectionUtils.isNotEmpty(supportedExtensions)) {
            for (String name : supportedExtensions) {
                instances.add(getExtension(name));
            }
        }
        
        instances.sort(Prioritized.COMPARATOR);
        return new LinkedHashSet<>(instances);
    }