/**
* @file nbody.c
- * @author Sam Moore (20503628) 2012
- * @purpose N-Body simulator - Definition of simulation functions; single threaded version
+ * @purpose Implentation of multi-threaded N-Body simulator using pthreads
+ * @author Sam Moore (20503628) - 2012
*/
-#include <stdlib.h>
-#include <stdio.h>
-#include <math.h>
-#include <time.h>
-#include <string.h>
-#include <stdbool.h>
+#include "nbody.h" // Declarations
+#include "../single-thread/nbody.c" // Include all functions from the single threaded version
-#include "nbody.h"
+#include "graphics.h" // For declaration of Graphics_Run only
-/**
- * Prints the body on screen
- */
-void Body_Print(Body * a)
-{
- printf("Body %p M=%f X=%f Y=%f Z=%f Fx=%f Fy=%f Fz=%f Vx=%f Vy=%f Vz=%f\n",
- (void*)a, a->mass, a->x[0], a->x[1], a->x[2], a->F[0], a->F[1], a->F[2], a->v[0], a->v[1], a->v[2]);
-}
+// --- Variable declarations --- //
-/**
- * Computing forces
- */
-void Body_Force(Body * a, System * s)
-{
- double distance;
- double con;
- double gd;
+pthread_t compute_thread; // The thread responsible for computations; it spawns worker threads
+
+pthread_t * worker_thread = NULL; //Array of worker threads responsible for Force and Position updates
+System * sub_system = NULL; //Array of Systems used to divide up the main "universe" System for worker threads
+pthread_mutex_t mutex_workers; // Mutex used for the barrier between Force and Position updates
+pthread_cond_t workers_done_cv; // Conditional used for the barrier between Force and Position updates
+unsigned workers_busy; // Number of workers currently doing something
- for (unsigned i = 0; i < DIMENSIONS; ++i)
- a->F[i] = 0;
+pthread_mutex_t mutex_runstate; // Mutex around the runstate
- for (unsigned index = 0; index < s->N; ++index)
- {
- Body * b = s->body+index;
- if (b == a)
- continue;
-
- distance = 0.0;
- for (unsigned i = 0; i < DIMENSIONS; ++i)
- distance += square(b->x[i] - a->x[i]);
- distance = sqrt(distance);
- con = G * a->mass * b->mass / square(distance);
- gd = con / distance;
- for (unsigned i = 0; i < DIMENSIONS; ++i)
- a->F[i] += gd * (b->x[i] - a->x[i]);
- }
-}
-/**
- * Compute velocities
- */
-void Body_Velocity(Body * a)
-{
- for (unsigned i = 0; i < DIMENSIONS; ++i)
- a->v[i] += a->F[i] / a->mass * DELTA_T;
-}
/**
- * Compute positions
+ * @function Compute_Thread
+ * @purpose Thread - Continuously computes steps for a system of bodies. Seperate from graphics functions.
+ * Spawns worker threads to divide up computation.
+ * @param arg - Can be cast to the System for which computations are performed (ie: &universe)
*/
-void Body_Position(Body * a)
+void * Compute_Thread(void * arg)
{
- for (unsigned i = 0; i < DIMENSIONS; ++i)
- a->x[i] += a->v[i] * DELTA_T;
-}
-/**
- * Main compute function
- */
-void System_Compute(System * s)
-{
-// clock_t start, finish;
+ System * s = (System*)(arg); //cast argument to a System*
+
-// start = clock();
+ // If no number of threads provided, use the default value, unless someone changed that to a stupid value
+ if (options.num_threads <= 0)
+ options.num_threads = (DEFAULT_WORKING_THREADS > 1) ? DEFAULT_WORKING_THREADS : 1;
- for (unsigned i = 0; i < s->N; ++i)
+ // Do a sanity check; there is no point spawning more threads than bodies.
+ if (options.num_threads > s->N)
{
- Body_Force(s->body+i, s);
- Body_Velocity(s->body+i);
- Body_Position(s->body+i);
+ fprintf(stderr,
+ "Warning: Using %u threads instead of %u specified, because there are only %u bodies to simulate!\n",
+ s->N, options.num_threads, s->N);
+ options.num_threads = s->N;
}
+
+ if (options.num_threads > 1) // Allocate worker threads and sub systems, as long as there would be more than 1
+ {
+ worker_thread = (pthread_t*)(calloc(options.num_threads, sizeof(pthread_t)));
+ if (worker_thread == NULL)
+ {
+ perror("Couldn't allocate array of worker threads");
+ QuitProgram(true);
+ pthread_exit(NULL);
+ }
+ sub_system = (System*)(calloc(options.num_threads, sizeof(System)));
+ if (sub_system == NULL)
+ {
+ perror("Couldn't allocate array of systems for worker threads to use");
+ QuitProgram(true);
+ pthread_exit(NULL);
+ }
-}
+ // Divide up the Body array owned by s into options.num_threads arrays, one for each worker thread
+ unsigned bodies_per_system = (s->N) / options.num_threads;
+ unsigned remainder = (s->N) % options.num_threads;
+ for (unsigned i = 0; i < options.num_threads; ++i)
+ {
+ sub_system[i].body = (s->body)+(i*bodies_per_system);
+ sub_system[i].N = bodies_per_system;
+ sub_system[i].steps = 0;
+ if (i == options.num_threads - 1)
+ sub_system[i].N += remainder; // The last thread gets the remainder
+ }
+ }
+ pthread_attr_t attr; //thread attribute for the workers.
+ pthread_attr_init(&attr);
+ pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED); //Needs to be detached, so that memory can be reused.
-/*
- * This function reads an input file. You can change it if you choose a
- * different file format
- */
-#define LINE_SIZE BUFSIZ
-void System_Init(System * s, char *fileName)
-{
- char line[LINE_SIZE];
- char * token;
- FILE * file;
+ // The main computation loop
+ while (true)
+ {
+ //Check whether the program should quit due to steps being computed, or a timeout
+ if (ExitCondition())
+ {
+ QuitProgram(false);
+ pthread_exit(NULL);
+ }
- file = fopen(fileName, "rt");
- s->N = atoi(fgets(line, LINE_SIZE, file));
- s->body = (Body*) calloc((size_t)s->N, sizeof(Body));
+ if (options.draw_graphics == false && options.verbosity != 0
+ && universe.steps % options.verbosity == 1)
+ {
+ DisplayStatistics();
+ }
- //printf("----------------------Initial field-------------------------------\n");
- for (unsigned i = 0; i < s->N; ++i)
- {
- if (fgets(line, LINE_SIZE, file) != NULL)
+ if (options.num_threads <= 1)
+ {
+ // Just do everything in this thread
+ System_Forces(s, s);
+ System_Positions(s);
+ continue;
+ }
+
+
+
+
+ workers_busy = options.num_threads; //All threads working
+
+ //Compute forces
+ for (unsigned i = 0; i < options.num_threads; ++i)
{
- Body * a = s->body+i;
- token = strtok(line, ",; ");
- a->mass = atof(token);
-
- for (unsigned j = 0; j < DIMENSIONS; ++j)
+ if (pthread_create(worker_thread+i, &attr, Force_Thread, (void*)(sub_system+i)) != 0)
{
- token = strtok(NULL, ",; ");
- a->x[j] = atof(token);
- }
- for (unsigned j = 0; j < DIMENSIONS; ++j)
+ perror("In compute thread, couldn't create worker thread (force)");
+ QuitProgram(true);
+ pthread_exit(NULL);
+ }
+ }
+
+
+
+ //Barrier - Wait for forces to be computed
+ pthread_mutex_lock(&mutex_workers);
+ while (workers_busy > 0)
+ pthread_cond_wait(&workers_done_cv, &mutex_workers);
+ pthread_mutex_unlock(&mutex_workers);
+
+ //All the forces are now computed
+
+ workers_busy = options.num_threads; //All threads working
+
+ //Compute positions
+ for (unsigned i = 0; i < options.num_threads; ++i)
+ {
+ if (pthread_create(worker_thread+i, &attr, Position_Thread, (void*)(sub_system+i)) != 0)
{
- token = strtok(NULL, ",; ");
- a->v[j] = atof(token);
- }
- //Body_Print(a);
+ perror("In compute thread, couldn't create worker thread (position)");
+ QuitProgram(true);
+ pthread_exit(NULL);
+ }
}
- }
- //printf("--------------------------------------------------------------\n");
-
- fclose(file);
+ //Wait for positions to be computed
+ pthread_mutex_lock(&mutex_workers);
+ while (workers_busy > 0)
+ pthread_cond_wait(&workers_done_cv, &mutex_workers);
+ pthread_mutex_unlock(&mutex_workers);
+
+ //Update number of steps computed
+ universe.steps += 1;
+
+
+
+ }
}
/**
- * Cleans up the universe by freeing all memory
+ * @function Force_Thread
+ * @purpose Thread - Calculates the forces on objects in a System
+ * @param s - Can be cast to the System*
*/
-void Universe_Cleanup()
+void * Force_Thread(void * s)
{
- free(universe.body);
- pthread_exit(NULL);
+
+ System_Forces((System*)s, &universe); //Simple wrapper
+
+ pthread_mutex_lock(&mutex_workers);
+ workers_busy -= 1; // Count this thread as done
+ if (workers_busy == 0)
+ {
+ pthread_cond_signal(&workers_done_cv); // All threads done; wake up the compute_thread
+ }
+ pthread_mutex_unlock(&mutex_workers);
+ return NULL;
}
/**
- * Thread - Continuously computes steps for a system of bodies
+ * @function Position_Thread
+ * @purpose Thread - Calculates the positions of objects in a System
+ * @param s - Can be cast to the System*
*/
-void * Compute_Thread(void * s)
+void * Position_Thread(void * s)
{
- while (true)
+
+ System_Positions((System*)s); // Simple wrapper
+
+ pthread_mutex_lock(&mutex_workers);
+ workers_busy -= 1; // Count this thread as done
+ if (workers_busy == 0)
{
- if (terminate) pthread_exit(NULL);
- System_Compute((System*)s);
+ pthread_cond_signal(&workers_done_cv); //All threads done; wake up the compute_thread
}
+ pthread_mutex_unlock(&mutex_workers);
+ return NULL;
+}
+
+/**
+ * @function QuitProgram
+ * @purpose This function can either be called by the main thread in order to signal other threads
+ * that it wants to exit. The main thread then calls pthread_join before exiting.
+ * It can also be called by a child thread to request the main thread to exit.
+ * It is only used this way if there is an unrecovarable error (ie: Can't allocate memory in a child thread)
+ */
+void QuitProgram(bool error)
+{
+ if (runstate == QUIT || runstate == QUIT_ERROR)
+ return; //Don't do anything if already quitting
+ pthread_mutex_lock(&mutex_runstate); // aquire mutex
+ if (error) // set the runstate
+ runstate = QUIT_ERROR;
+ else
+ runstate = QUIT;
+ pthread_mutex_unlock(&mutex_runstate); //release mutex
+}
+
+/**
+ * @function Thread_Cleanup
+ * @purpose Will be called in the main thread when exit() is called
+ * Automatically tells all other threads to quit (if they haven't already been told)
+ * Then waits for them to finish.
+ * Also frees memory associated with the worker threads.
+ */
+void Thread_Cleanup(void)
+{
+ if (runstate == RUN) // If this is true, as far as child threads are concerned, the simulation is still running
+ QuitProgram(false); // So call QuitProgram which will set runstate, and cause child threads to exit
+ pthread_join(compute_thread, NULL);
+ free(worker_thread);
+ free(sub_system);
}
+/**
+ * @function Simulation_Run
+ * @purpose Initialise and start the simulation. Will be called in the main thread.
+ * Replaces the single-threaded macro that does nothing, and sets up the compute thread
+ * @param argc - Number of arguments - Passed to Graphics_Run if needed
+ * @param argv - Argument strings - Passed to Graphics_Run if needed
+ */
+void Simulation_Run(int argc, char ** argv)
+{
+ atexit(Thread_Cleanup);
+ if (options.draw_graphics)
+ {
+ // The graphics are enabled, so create a thread to do computations
+ // Graphics are done in the main loop
+ if (pthread_create(&compute_thread, NULL, Compute_Thread, (void*)&universe) != 0)
+ {
+ perror("Error creating compute thread");
+ exit(EXIT_FAILURE);
+ }
+ Graphics_Run(argc, argv);
+ }
+ else
+ Compute_Thread((void*)(&universe)); // Graphics are disabled, so do computations in the main thread
+}
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