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Java fork join
- 1. Java Fork Join MASUDHASAN
- 2. Some history Untilrecently, most computers only had 1 processing core Multithreading was simulated on a single core Not true concurrency Serial approach to algorithms often sufficed
- 3. multicore Concurrency andperformance are tied together Real concurrency – separate threads can execute on different cores at the same time The JVM runtime controls scheduling
- 4. Fork and JoinFramework Some types of algorithms exist that require tasks to create subtasks and communicate with each other to complete. Those are the “divide and conquer” algorithms, which are also referred to as “map and reduce,”
- 5. Example: partial sumsof an Array of Integers Divide the array into the number n of available physical processing units Create Callable instances to compute each partial sum Submit them to an executor managing a pool of n threads Collect the result to compute the final sum
- 6. Fork Join Thecore addition is a new ForkJoinPool executor that is dedicated to running instances implementing ForkJoinTask. ForkJoinTask objects feature two specific methods: fork(): allows a ForkJoinTask to be planned for asynchronous execution join() method allows a ForkJoinTask to wait for the completion of another one There are 2 types of ForkJoinTask: RecursiveAction represent executions that do not yield a return value Instances RecursiveTask yields return values
- 7. ForkJoinPool Implements ExecutorService Autosizing workers Double‐ended queue Workstealing algorithm
- 8. Pooling/ExecutorService then why Coarse‐grained independent tasks Recursively decomposed tasks spend most Cme waiCng In normal threadpool: starvaCon Task‐queue of threadpool‐backed ExecutorService not opCmized f or many small tasks No workstealing
- 9. Map/Reduce FORK/JOIN HADOOP MAP/REDUCE EnvironmentSingle JVM Cluster Model Recursive forking Often single map Scales with Cores/CPUs Nodes Worker interaction Workstealing No inter‐node communicati on
- 10. Fork Join &JAVA EE ForkJoinPool starts threads Illegal in EJBs Fair game in servlets/CDI beans Don’t create ForkJoinPool for each request Idea: WorkManager to create poolthreads Single pool, async submit(ForkJoinTask) Don’t Ce up request thread: Servlet 3.0
- 11. Other concurrency models Actors (AKKA) Sofware transactional memory Dataflow concurrency (AKKA) Agents