java 基于 MemCache 的队列实现
在用Memcache 的时候，想有一个类似于队列的功能。import java.util.Collection;
import com.danga.MemCached.MemCachedClient;
/**
* 基于MemCache的一个队列实现
* @author v_tianyongjun
*
*/
public class MemCacheQueue<T>{
private static final String KEY_SIZE = "_size";
private static final String KEY_OFFSET = "_offset";
private static final String KEY = "_key";
private static final String LOCK = "_lock";
private MemCachedClient mcc ;
private String name ;
public MemCacheQueue(String name , MemCachedClient mcc) {
this.mcc = mcc ;
this.name = name ;
mcc.set( name + KEY_SIZE , 0);
mcc.set( name + KEY_OFFSET , 0);
}
/**
* 向队列里添加一个元素
* @param t
*/
public void push(T t){
lock();
int size = getSize();
mcc.set( name + KEY + "_" + size, t);
mcc.set( name + KEY_SIZE , size + 1 );
unlock();
}
public void pushAll(Collection<T> ts){
lock();
int _size = ts.size() ;
int size = getSize();
int c = 0 ;
for( T t : ts){
mcc.set( name + KEY + "_" + (size + c++), t);
}
mcc.set( name + KEY_SIZE , size + _size );
unlock();
}
/**
* 读取队头
* @return
*/
public T peek(){
int offset = getOffset();
@SuppressWarnings("unchecked")
T t = (T) mcc.get( name + KEY + "_" + offset );
return t ;
}
/**
* 读取并删除队头
* @return
*/
public T poll(){
lock();
T t = peek();
int offset = getOffset();
mcc.delete( name + KEY + "_" + offset );
mcc.set( name + KEY_OFFSET , offset + 1 );
unlock();
return t;
}
public void clear(){
lock();
int size = getSize();
int offset = getOffset();
for( int i = 0 ; i < size ; i++){
mcc.delete(name + KEY + "_" + ( offset + i ) );
}
mcc.delete( name + KEY_SIZE );
mcc.delete( name + KEY_OFFSET );
unlock();
}
/**
* @return
*/
public int getSize() {
Integer size = (Integer) mcc.get(name+KEY_SIZE);
if( size == null ){
size = 0 ;
}
return size;
}
private int getOffset(){
Integer off = (Integer) mcc.get(name+KEY_OFFSET);
if( off == null ){
off = 0 ;
}
return off;
}
private void lock(){
while(true){
Long lock = mcc.addOrDecr(name+LOCK,1);
if( lock == 1 ) {
return;
}
try {
Thread.sleep(10);
} catch (InterruptedException e) {}
}
}
private void unlock(){
mcc.delete(name+LOCK);
}
}
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