sequential concurrency ... what ???

Download Sequential Concurrency ... WHAT ???

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Using the ThreadPool, we cannot ensure the execution order of the tasks. There are few situations as per the industry needs, where we need to ensure the task execution order. StripedExecutorService class we are developing, would ensure the task execution order. Example: On an Exchange server we have many products on which users can trade. Transactions on a single product should be performed in FIFO order as per the business needs, and there are many products of such type. So along with maintaining the sequential order of execution of tasks for A product, we are also processing tasks sequentially for other product B as well concurrently. We would be showing Heinz Kabutz implementation.

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  • 1. Jitendra Chittoda, Member Development Department @ ION Trading IndiaPvt. Ltd.Co-leader Delhi and NCR Java User Group (DaNJUG)Email: jitendra@chittoda.comTwitter: @JChittodaBlog: http://chittoda.comSequential Concurrency. WHAT???08 May 20131JavaOne India 2013 : COM1240

2. Delhi & NCR JUG (DaNJUG)08 May 20132 30+ Members Looking for more active members Meetup.com, Groups If your friends are in Delhi NCR, please spreadthe word 3. Agenda What is ThreadPool Benefits of using ThreadPool What we cant achieve with ThreadPool Why & Where ? Sequential Concurrency Fundamentals SerialExecutor StripedExecutorService Design Features Current State08 May 20133 4. ThreadPool08 May 20134 5. Benefits of ThreadPool08 May 20135 Pre-initialized pool of threads Reusable threads Configurable 6. What we cant achieve withThreadPool08 May 20136 As per the business requirement, sometimes youmay want to process Tasks in specific order. Tasks execution order is not maintained by thenormal ThreadPools Processing Not Ordered Processing of a Task is not ordered, you can say itsuncertain. 7. 08 May 20137 8. Why? Industry Examples08 May 20138 Exchange trading Processing of trades on an instrument. Train Reservations Ticket booking requests for a train must beprocessed in FIFO order. Multi Tenancy Each tenant want some specific execution to beordered 9. Where ?08 May 20139 First saw in 2007 then in 2010 and in 2011 November 2011: Started writing my ownimplementation, published a blog onhttp://chittoda.com November 2012: http://www.javaspecialists.eu/archive/Issue206.html Heinz got 5 different implementations after thisissue. 10. Sequential ConcurrencyFundamentals08 May 201310IdentificationMaintaining OrderSequential ProcessingNo Dependency 11. Sequential ConcurrencyFundamentals08 May 201311 Identification Maintain the sequence based on some Stripe orKey Stripe: An object which is common among theTasks those needs to be processed in sequence. 12. Sequential ConcurrencyFundamentals08 May 201312 Maintaining Order Maintain the sequential ordering tasks FIFO Order 13. Sequential ConcurrencyFundamentals08 May 201313 Sequential Processing Process tasks of a Stripe in sequence To maintain this we assign one and only one Thread to aQueue. 14. Sequential ConcurrencyFundamentals08 May 201314 No Dependency Tasks of one Stripe-X should not be dependent on Tasks ofanother Stripe-Y 15. Sequential Concurrency08 May 20131512 132Pool ofThreadsQueue ofStripeStripedExecutorServiceT-1T-2T-3 16. Executor JavaDoc08 May 201316 Many Executor implementations impose some sort oflimitation on how and when tasks are scheduled. Theexecutor below serializes the submission of tasks to asecond executor, illustrating a composite executor.class SerialExecutor implements Executor {Queue tasks = new ArrayDeque();Executor executor;Runnable active;SerialExecutor(Executor executor) {this.executor = executor;} 17. SerialExecutor08 May 201317public void execute(final Runnable r) {tasks.offer(new Runnable() {public void run() {try {r.run();} finally {scheduleNext();}}});if (active == null) {scheduleNext();}} 18. SerialExecutor08 May 201318protected void scheduleNext() {if ((active = tasks.poll()) != null) {executor.execute(active);}} 19. Pool of SerialExecutor08 May 201319 SerialExecutor maintain the sequence of thetasks assigned to it and process them insequence. Using single queue. BUT we need pool of SerialExecutor, so that wecan concurrently execute tasks of two or moreStriped Queues 20. Implementation Details08 May 2013201) Identification Stripe: We are using Object as Stripe, you candefine your own.2) Maintain Order With separate Queue based on Stripe. SerialExecutor is maintaining a Queue3) Sequential Processing Handled by SerialExecutor4) No Dependency Handled by SerialExecutor 21. Design08 May 201321 22. 08 May 201322 23. 08 May 201323 24. Inside StripedExecutorService08 May 201324class SerialExecutor implements Executor {private BlockingQueue tasks =new LinkedBlockingQueue();private Runnable active;private final Object stripe;private SerialExecutor(Object stripe) {this.stripe = stripe;} 25. 08 May 201325public void execute(final Runnable r) {lock.lock();try {tasks.add(new Runnable() {public void run() {try {r.run();} finally { scheduleNext(); }}});if (active == null){ scheduleNext(); }} finally {lock.unlock();}} 26. Inside StripedExecutorService08 May 201326private void scheduleNext() {lock.lock();try {if ((active = tasks.poll()) != null) {executor.execute(active);terminating.signalAll();} else {removeEmptySerialExecutor(stripe, this);}} finally {lock.unlock();}} 27. 08 May 201327private final ExecutorService executor;private final Map executors =new IdentityHashMap();public void execute(Runnable command) {lock.lock();try {Object stripe = getStripe(command);if (stripe != null) {SerialExecutor ser_exec=executors.get(stripe);if (ser_exec == null) {executors.put(stripe, ser_exec=new SerialExecutor(stripe));}ser_exec.execute(command);} else { executor.execute(command); }} finally { lock.unlock(); }} 28. Features08 May 201328 Non striped tasks can also be handled with SES Queues gets created when required No memory leaks in terms of the Queues. Queuesgets removed once all tasks are finished. 29. Current State08 May 201329 Work In Progress Several other implementations available, but noone passes the tests written forStripedExecutorService Performance 30. References08 May 201330 Delhi & NCR JUG https://groups.google.com/d/forum/dncrjug GitHub : https://github.com/kabutz/striped-executor-service Dr. Heinz Kabutz Newsletter http://www.javaspecialists.eu/archive/Issue206.html http://www.javaspecialists.eu/ Blog http://chittoda.com 31. 08 May 201331

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