Java concurrency introduction

1. Java Concurrency Introduction yangwm http://t.sina.com.cn/yangwm

2. - Java Memory Model - Thread coordinate and Synchronize - Lock Blocking and Contention - Java Util Concurrent - Fork/Join, Coroutine

3. Java Memory Model: 1. Atomicity, Visibility,Ordering 2. main memory, working memory 3, safe publication happends-before ordering: synchronized:Atomicity, Visibility,Ordering volatile:Visibility(access main memory),Ordering final java.util.concurrent.locks java.util.concurrent.atmoic ... ThreadLocal ： keep state with a thread cache objects which you need frequently

4. Thread coordinate and Synchronize: interrupt: throw InterruptedException or Thread.currentThread().interrupt() synchronized vs lock Condition await() -> wait() signal() -> notify() signalAll() -> notifyAll() LockSupport park() unpark()

5. Lock Blocking : suspending spin-waiting

6. Lock Contention : 1. 减少锁持有的时间 2. 减少锁请求的频率 3. 采用共享锁取代独占锁 lock separate: read write lock split lock-free: cas

7. Java Util Concurrent : AtomicInteger: visibility: volatile nonblocking: for(;;) + compare-and-swap(cpu instruct: read-modify-write) ReentrantLock : NonfairSync vs FairSync ReentrantReadWriteLock : volatile int value; AbstractQueuedSynchronizer: synchronization state; blocking and unblocking threads Queues: CLH FutureTask, CountDownLatch, CyclicBarrier, Exchanger

8. Amdahl's Law 1 / ((1 - P) + (P / N)) P is the proportion of a program that can be made parallel (1 − P) is the proportion that cannot be parallelized (remains serial) N is processors

9. remind batch simple process flow : 1. split uids to uid array 2. local cache check source(appkey) for { 3. hash by uid 4. get jedis connection by hash 5. do something with jedis connection 6. release jedis connection 7. return resultBean and to json or xml }

10. remind batch optimization process flow : 1. get jedis connection while(1){ 2. get something message by queue 3. do something with jedis connection } 4. get jedis connection 1. split uids to uid array 2. local cache check source(appkey) for { 3. hash by uid 4. put something message to queue by hash 5. return resultBean and to json or xml }

11. Concurrent Collection: ConcurrentMap : ConcurrentHashMap/ConcurrentSkipListMap queue: ConcurrentLinkedQueue BlockingQueue: SynchronousQueue/ArrayBlockingQueue/LinkedBlockingQueue copy-on-write: CopyOnWriteArrayList/CopyOnWriteArraySet

12. ThreadPoolExecutor : power and flexible 1. strategy create and destory strategy handle workqueue task handle excess task hook function extend behaviour 2. Concrete Implement ： 1 ）当 workerCount 小于 corePoolSize 就新建线程，并处理请求 2 ）当 workerCount 大于等于 corePoolSize ，把请求放入 workQueue 中，空闲线程就去从 workQueue 中取任务并处理 3 ）当 workQueue 放不下新入的任务时，新建 worker 加入 pool ，并处理请求，如果 workerCount 大小撑到了 maximumPoolSize 就用 RejectedExecutionHandler 来做拒绝处理

13. Fork/Join Framework Fork/Join parallelism is among the simplest and most effective design techniques for obtaining good parallel performance. Result solve(Problem problem) { if (problem is small) { directly solve problem } else { split problem into independent parts fork new subtasks to solve each part join all subtasks compose result from subresults } }

14. Coroutine: Kilim is a message-passing framework for Java that provides ultra-lightweight threads and facilities for fast, safe, zero-copy messaging

15. thank you