序
本文主要研究一下dubbo的ConcurrentHashSet
ConcurrentHashSet
dubbo-2.7.2/dubbo-common/src/main/java/org/apache/dubbo/common/utils/ConcurrentHashSet.java
public class ConcurrentHashSet<E> extends AbstractSet<E> implements Set<E>, java.io.Serializable {
private static final long serialVersionUID = -8672117787651310382L;
private static final Object PRESENT = new Object();
private final ConcurrentMap<E, Object> map;
public ConcurrentHashSet() {
map = new ConcurrentHashMap<E, Object>();
}
public ConcurrentHashSet(int initialCapacity) {
map = new ConcurrentHashMap<E, Object>(initialCapacity);
}
/**
* Returns an iterator over the elements in this set. The elements are
* returned in no particular order.
*
* @return an Iterator over the elements in this set
* @see ConcurrentModificationException
*/
@Override
public Iterator<E> iterator() {
return map.keySet().iterator();
}
/**
* Returns the number of elements in this set (its cardinality).
*
* @return the number of elements in this set (its cardinality)
*/
@Override
public int size() {
return map.size();
}
/**
* Returns <tt>true</tt> if this set contains no elements.
*
* @return <tt>true</tt> if this set contains no elements
*/
@Override
public boolean isEmpty() {
return map.isEmpty();
}
/**
* Returns <tt>true</tt> if this set contains the specified element. More
* formally, returns <tt>true</tt> if and only if this set contains an
* element <tt>e</tt> such that
* <tt>(o==null ? e==null : o.equals(e))</tt>.
*
* @param o element whose presence in this set is to be tested
* @return <tt>true</tt> if this set contains the specified element
*/
@Override
public boolean contains(Object o) {
return map.containsKey(o);
}
/**
* Adds the specified element to this set if it is not already present. More
* formally, adds the specified element <tt>e</tt> to this set if this set
* contains no element <tt>e2</tt> such that
* <tt>(e==null ? e2==null : e.equals(e2))</tt>. If this
* set already contains the element, the call leaves the set unchanged and
* returns <tt>false</tt>.
*
* @param e element to be added to this set
* @return <tt>true</tt> if this set did not already contain the specified
* element
*/
@Override
public boolean add(E e) {
return map.put(e, PRESENT) == null;
}
/**
* Removes the specified element from this set if it is present. More
* formally, removes an element <tt>e</tt> such that
* <tt>(o==null ? e==null : o.equals(e))</tt>, if this
* set contains such an element. Returns <tt>true</tt> if this set contained
* the element (or equivalently, if this set changed as a result of the
* call). (This set will not contain the element once the call returns.)
*
* @param o object to be removed from this set, if present
* @return <tt>true</tt> if the set contained the specified element
*/
@Override
public boolean remove(Object o) {
return map.remove(o) == PRESENT;
}
/**
* Removes all of the elements from this set. The set will be empty after
* this call returns.
*/
@Override
public void clear() {
map.clear();
}
}
- ConcurrentHashSet继承了AbstractSet，实现了Set、Serializable接口；它底层使用ConcurrentHashMap来实现，其value固定为PRESENT
实例
dubbo-2.7.2/dubbo-config/dubbo-config-spring/src/main/java/org/apache/dubbo/config/spring/extension/SpringExtensionFactory.java
public class SpringExtensionFactory implements ExtensionFactory {
private static final Logger logger = LoggerFactory.getLogger(SpringExtensionFactory.class);
private static final Set<ApplicationContext> CONTEXTS = new ConcurrentHashSet<ApplicationContext>();
private static final ApplicationListener SHUTDOWN_HOOK_LISTENER = new ShutdownHookListener();
public static void addApplicationContext(ApplicationContext context) {
CONTEXTS.add(context);
if (context instanceof ConfigurableApplicationContext) {
((ConfigurableApplicationContext) context).registerShutdownHook();
DubboShutdownHook.getDubboShutdownHook().unregister();
}
BeanFactoryUtils.addApplicationListener(context, SHUTDOWN_HOOK_LISTENER);
}
public static void removeApplicationContext(ApplicationContext context) {
CONTEXTS.remove(context);
}
public static Set<ApplicationContext> getContexts() {
return CONTEXTS;
}
// currently for test purpose
public static void clearContexts() {
CONTEXTS.clear();
}
@Override
@SuppressWarnings("unchecked")
public <T> T getExtension(Class<T> type, String name) {
//SPI should be get from SpiExtensionFactory
if (type.isInterface() && type.isAnnotationPresent(SPI.class)) {
return null;
}
for (ApplicationContext context : CONTEXTS) {
if (context.containsBean(name)) {
Object bean = context.getBean(name);
if (type.isInstance(bean)) {
return (T) bean;
}
}
}
logger.warn("No spring extension (bean) named:" + name + ", try to find an extension (bean) of type " + type.getName());
if (Object.class == type) {
return null;
}
for (ApplicationContext context : CONTEXTS) {
try {
return context.getBean(type);
} catch (NoUniqueBeanDefinitionException multiBeanExe) {
logger.warn("Find more than 1 spring extensions (beans) of type " + type.getName() + ", will stop auto injection. Please make sure you have specified the concrete parameter type and there's only one extension of that type.");
} catch (NoSuchBeanDefinitionException noBeanExe) {
if (logger.isDebugEnabled()) {
logger.debug("Error when get spring extension(bean) for type:" + type.getName(), noBeanExe);
}
}
}
logger.warn("No spring extension (bean) named:" + name + ", type:" + type.getName() + " found, stop get bean.");
return null;
}
private static class ShutdownHookListener implements ApplicationListener {
@Override
public void onApplicationEvent(ApplicationEvent event) {
if (event instanceof ContextClosedEvent) {
DubboShutdownHook shutdownHook = DubboShutdownHook.getDubboShutdownHook();
shutdownHook.doDestroy();
}
}
}
}
- SpringExtensionFactory实现了ExtensionFactory接口，它使用ConcurrentHashSet来注册spring的ApplicationContext
小结
ConcurrentHashSet继承了AbstractSet，实现了Set、Serializable接口；它底层使用ConcurrentHashMap来实现，其value固定为PRESENT
