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一个cache的改造过程

发布时间:2019-10-13 06:57:52 编辑:笔名

  在分布式的程序中,cache的合理使用可以带来性能上的极大提升,尤其是在资源创建需要昂贵的开销时。cache的设计最重要的是要保证线程安全和高效性。下面以代码为例,介绍了三种cache的写法。

  1. 粗放的加锁

  public class Cache1 { private HashMapString, ServerGroup route2SG = null; public Cache1() { route2SG = new HashMapString, ServerGroup(); } public synchronized ServerGroup get(String routeKey) throws IOException { ServerGroup sg = null; sg = t(routeKey); if (sg == null) { sg = getServerGroup(routeKey); t(routeKey, sg); } return sg; } public synchronized void remove(String routeKey) { move(routeKey); } private ServerGroup getServerGroup(String routeKey) throws IOException { ServerGroup sg = null; /** * Construct ServerGroup here */ return sg; } }2. 读写锁

  public class Cache2 { private ConcurrentHashMapString, ServerGroup route2SG = null; private final ReadWriteLock lock = new ReentrantReadWriteLock(); public Cache2() { route2SG = new ConcurrentHashMapString, ServerGroup(); } public ServerGroup get(String routeKey) throws IOException { ServerGroup sg = null; try { adLock().lock(); sg = t(routeKey); if (sg == null) { adLock().unlock(); iteLock().lock(); sg = t(routeKey); if (sg == null) { sg = getServerGroup(routeKey); t(routeKey, sg); } adLock().lock(); iteLock().unlock(); } } catch (IOException e) { iteLock().unlock(); throw (e); } adLock().unlock(); return sg; } public void remove(String routeKey) { try { iteLock().lock(); move(routeKey); } finally { iteLock().unlock(); } } private ServerGroup getServerGroup(String routeKey) throws IOException { ServerGroup sg = null; /** * Construct ServerGroup here */ return sg; } }3. 无锁

  public class Cache3 { private ConcurrentHashMapString, FutureTaskServerGroup route2SGFT = null; public Cache3() { route2SGFT = new ConcurrentHashMapString, FutureTaskServerGroup(); } public ServerGroup get(String routeKey) throws IOException, InterruptedException, ExecutionException { FutureTaskServerGroup ft = t(routeKey); if (ft != null) { return t(); } FutureTaskServerGroup sft = new FutureTaskServerGroup(new ConstructSGTask(routeKey)); FutureTaskServerGroup old = tIfAbsent(routeKey, sft); if (old == null) { old=sft; n(); } return t(); } public void remove(String routeKey) { move(routeKey); } class ConstructSGTask implements CallableServerGroup { private final String key; public ConstructSGTask(String key) { super(); y = key; } @Override public ServerGroup call() throws Exception { return getServerGroup(key); } } private ServerGroup getServerGroup(String routeKey) throws IOException { ServerGroup sg = null; /** * Construct ServerGroup here */ return sg; } }总结,

  从三份代码中可以看出,锁的粒度从粗放到无,这个就极大的提高了cache的并发性。

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