course/semester2/pprog/assignment1/openmp/nbody.c

   1 /**
   2  * @file nbody.c
   3  * @purpose OpenMP version of N-Body simulator, implementation
   4  * @author Sam Moore (20503628) - 2012
   5  */
   6
   7 #include "nbody.h"
   8 #include "../single-thread/nbody.c" // Include original code
   9 #include "graphics.h" // For Graphics_Run function only
  10
  11 /**
  12  * @function Simulation_Run
  13  * @purpose Start the simulation
  14  * @param argc, argv - Passed to Graphics_Run if needed, otherwise unused
  15  */
  16 void Simulation_Run(int argc, char ** argv)
  17 {
  18         omp_set_nested(1);
  19         if (omp_get_nested() != 1)
  20         {
  21                 fprintf(stderr, "Couldn't set nested parallelism, I kind of need that\n");
  22                 exit(EXIT_FAILURE);
  23         }
  24
  25
  26         if (options.num_threads == 0)
  27                 options.num_threads = omp_get_max_threads();
  28
  29         if (options.draw_graphics)
  30                 omp_set_num_threads(2);
  31         else
  32                 omp_set_num_threads(1);
  33
  34
  35
  36
  37         #pragma omp parallel sections
  38         {
  39
  40                 #pragma omp section
  41                 {
  42                         omp_set_num_threads(options.num_threads);
  43                         while (true)
  44                         {
  45
  46                                 if (runstate != RUN) break; //Check whether the main thread wants to exit
  47
  48                                 if (ExitCondition())
  49                                 {
  50                                         break;
  51                                 }
  52
  53
  54                                 if (options.draw_graphics == false && options.verbosity != 0
  55                                         && universe.steps % options.verbosity == 1)
  56                                 {
  57                                         DisplayStatistics();
  58                                 }
  59
  60
  61                                 Compute();
  62                         }
  63                         //printf("Left compute loop\n");
  64                 }
  65
  66                 #pragma omp section
  67                 {
  68                         if (options.draw_graphics)
  69                                 Graphics_Run(argc, argv);
  70                         //printf("Got to bit after Graphics_Run()\n");
  71                 }
  72
  73         }
  74 }
  75
  76 /**
  77  * @function Compute
  78  * @purpose Compute a single step, multithreaded using OpenMP
  79  */
  80 void Compute(void)
  81 {
  82         //printf("There are %d threads working and %d available\n", omp_get_num_threads(), omp_get_max_threads());
  83         //return;
  84         unsigned n_per_thread = (universe.N) / options.num_threads;
  85         unsigned remainder = (universe.N) % options.num_threads;
  86         #pragma omp parallel for
  87         for (unsigned i = 0; i < options.num_threads; ++i)
  88         {
  89                 //printf("Thread %d executes iteration %u\n", omp_get_thread_num(), i);
  90                 System s;
  91                 s.body = universe.body + (i * n_per_thread);
  92                 s.N = (i == options.num_threads - 1) ? n_per_thread : n_per_thread + remainder;
  93                 System_Forces(&s, &universe);
  94         }
  95
  96         #pragma omp parallel for
  97         for (unsigned i = 0; i < options.num_threads; ++i)
  98         {
  99                 //printf("Thread %d executes iteration %u\n", omp_get_thread_num(), i);
 100                 System s;
 101                 s.body = universe.body + (i * n_per_thread);
 102                 s.N = (i == options.num_threads - 1) ? n_per_thread : n_per_thread + remainder;
 103                 System_Positions(&s);
 104         }
 105
 106         universe.steps += 1;
 107
 108 }