虚拟化--026 vsphere HA 配置 步骤

HashTable为线程安全的Map对象，但是现在的JDK不提倡使用HashTable

而日常推荐使用的HashMap为非线程安全的对象，通过java.util.Collections可以把HashMap变为线程安全，在需要多线程环境中实现同步时使用。

Map map = Collections.synchronizedMap(new HashMap());

一下内容为JDK中实现的Map同步代码

private static class SynchronizedMap<K,V>
implements Map<K,V>, Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 1978198479659022715L;

private Map<K,V> m; // Backing Map
Object mutex; // Object on which to synchronize

SynchronizedMap(Map<K,V> m) {
if (m==null)
throw new NullPointerException();
this.m = m;
mutex = this;
}

SynchronizedMap(Map<K,V> m, Object mutex) {
this.m = m;
this.mutex = mutex;
}

public int size() {
synchronized(mutex) {return m.size();}
}
public boolean isEmpty(){
synchronized(mutex) {return m.isEmpty();}
}
public boolean containsKey(Object key) {
synchronized(mutex) {return m.containsKey(key);}
}
public boolean containsValue(Object value){
synchronized(mutex) {return m.containsValue(value);}
}
public V get(Object key) {
synchronized(mutex) {return m.get(key);}
}

public V put(K key, V value) {
synchronized(mutex) {return m.put(key, value);}
}
public V remove(Object key) {
synchronized(mutex) {return m.remove(key);}
}
public void putAll(Map<? extends K, ? extends V> map) {
synchronized(mutex) {m.putAll(map);}
}
public void clear() {
synchronized(mutex) {m.clear();}
}

private transient Set<K> keySet = null;
private transient Set<Map.Entry<K,V>> entrySet = null;
private transient Collection<V> values = null;

public Set<K> keySet() {
synchronized(mutex) {
if (keySet==null)
keySet = new SynchronizedSet<K>(m.keySet(), mutex);
return keySet;
}
}

public Set<Map.Entry<K,V>> entrySet() {
synchronized(mutex) {
if (entrySet==null)
entrySet = new SynchronizedSet<Map.Entry<K,V>>((Set<Map.Entry<K,V>>)m.entrySet(), mutex);
return entrySet;
}
}

public Collection<V> values() {
synchronized(mutex) {
if (values==null)
values = new SynchronizedCollection<V>(m.values(), mutex);
return values;
}
}

public boolean equals(Object o) {
synchronized(mutex) {return m.equals(o);}
}
public int hashCode() {
synchronized(mutex) {return m.hashCode();}
}
public String toString() {
synchronized(mutex) {return m.toString();}
}
private void writeObject(ObjectOutputStream s) throws IOException {
synchronized(mutex) {s.defaultWriteObject();}
}
}