2. Agenda Background Multiprocessing Programming Preference Programming Model Parallel Section Clauses Synchronization

3. Background Parallel has no semantic impact Concurrency has a substantial semantic impact

4. Background Symmetric Multi Processor(SMP) Shared Memory Multiprocessing Programming OpenMP Massively Parallel Processor(MPP) Message Passing Interface Programming MPI

5. Background

6. Multiprocessing Programming

7. Multiprocessing Programming General Threading Model Main thread executes the program’s main function Main thread creates subthreads, witch execute other functions in the program. Subthreads can also create additional threads.

8. Multiprocessing Programming Benefits Increased performance and better resource utilization Even on single processor systems – for hiding latency and increasing throughput IPC thread shared memory is more efficient Risk Increases complexity of the application Difficult to debug (data races, deadlocks, etc.)

9. OpenMP Preference (later VS2005)

10. OpenMP Preference (later GCC 4.2)

11. Programming Model Generate multi-thread code by referencing directive code Compiler is required to support openMP To eliminate synchronization and dependency

12. Programming Model

13. Parallel Section (for) #pragmaomp for [clause [clause …] ] { for loop }

14. Parallel Section (sections) #pragmaomp sections [clause [clause …] ] { [#progmaomp section] structured code block }

15. Clauses private(var1, …) to block sharing selected values with threads shared(var1, …) to share selected values with threads schedule(type [, chunk_size]) to divide work with threads for equality static dynamic

16. Synchronization (critical section) Declaring critical section in parallel section Running only single thread at moment #pragmaomp critical [(name)] { structured code block }

17. https://computing.llnl.gov/tutorials/openMP/