3 * @purpose Implentation of multi-threaded N-Body simulator using pthreads
4 * @author Sam Moore (20503628) - 2012
7 #include "nbody.h" // Declarations
8 #include "../single-thread/nbody.c" // Include all functions from the single threaded version
10 #include "graphics.h" // For declaration of Graphics_Run only
12 // --- Variable declarations --- //
14 pthread_t compute_thread; // The thread responsible for computations; it spawns worker threads
16 pthread_t * worker_thread = NULL; //Array of worker threads responsible for Force and Position updates
17 System * sub_system = NULL; //Array of Systems used to divide up the main "universe" System for worker threads
18 pthread_mutex_t mutex_workers; // Mutex used for the barrier between Force and Position updates
19 pthread_cond_t workers_done_cv; // Conditional used for the barrier between Force and Position updates
20 unsigned workers_busy; // Number of workers currently doing something
22 pthread_mutex_t mutex_runstate; // Mutex around the runstate
27 * @function Compute_Thread
28 * @purpose Thread - Continuously computes steps for a system of bodies. Seperate from graphics functions.
29 * Spawns worker threads to divide up computation.
30 * @param arg - Can be cast to the System for which computations are performed (ie: &universe)
32 void * Compute_Thread(void * arg)
35 System * s = (System*)(arg); //cast argument to a System*
38 // If no number of threads provided, use the default value, unless someone changed that to a stupid value
39 if (options.num_threads <= 0)
40 options.num_threads = (DEFAULT_WORKING_THREADS > 1) ? DEFAULT_WORKING_THREADS : 1;
42 // Do a sanity check; there is no point spawning more threads than bodies.
43 if (options.num_threads > s->N)
46 "Warning: Using %u threads instead of %u specified, because there are only %u bodies to simulate!\n",
47 s->N, options.num_threads, s->N);
48 options.num_threads = s->N;
51 if (options.num_threads > 1) // Allocate worker threads and sub systems, as long as there would be more than 1
53 worker_thread = (pthread_t*)(calloc(options.num_threads, sizeof(pthread_t)));
54 if (worker_thread == NULL)
56 perror("Couldn't allocate array of worker threads");
60 sub_system = (System*)(calloc(options.num_threads, sizeof(System)));
61 if (sub_system == NULL)
63 perror("Couldn't allocate array of systems for worker threads to use");
68 // Divide up the Body array owned by s into options.num_threads arrays, one for each worker thread
69 unsigned bodies_per_system = (s->N) / options.num_threads;
70 unsigned remainder = (s->N) % options.num_threads;
71 for (unsigned i = 0; i < options.num_threads; ++i)
73 sub_system[i].body = (s->body)+(i*bodies_per_system);
74 sub_system[i].N = bodies_per_system;
75 sub_system[i].steps = 0;
76 if (i == options.num_threads - 1)
77 sub_system[i].N += remainder; // The last thread gets the remainder
83 pthread_attr_t attr; //thread attribute for the workers.
84 pthread_attr_init(&attr);
85 pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED); //Needs to be detached, so that memory can be reused.
87 // The main computation loop
90 //Check whether the program should quit due to steps being computed, or a timeout
97 if (options.draw_graphics == false && options.verbosity != 0
98 && universe.steps % options.verbosity == 1)
104 if (options.num_threads <= 1)
106 // Just do everything in this thread
115 workers_busy = options.num_threads; //All threads working
118 for (unsigned i = 0; i < options.num_threads; ++i)
120 if (pthread_create(worker_thread+i, &attr, Force_Thread, (void*)(sub_system+i)) != 0)
122 perror("In compute thread, couldn't create worker thread (force)");
130 //Barrier - Wait for forces to be computed
131 pthread_mutex_lock(&mutex_workers);
132 while (workers_busy > 0)
133 pthread_cond_wait(&workers_done_cv, &mutex_workers);
134 pthread_mutex_unlock(&mutex_workers);
136 //All the forces are now computed
138 workers_busy = options.num_threads; //All threads working
141 for (unsigned i = 0; i < options.num_threads; ++i)
143 if (pthread_create(worker_thread+i, &attr, Position_Thread, (void*)(sub_system+i)) != 0)
145 perror("In compute thread, couldn't create worker thread (position)");
151 //Wait for positions to be computed
152 pthread_mutex_lock(&mutex_workers);
153 while (workers_busy > 0)
154 pthread_cond_wait(&workers_done_cv, &mutex_workers);
155 pthread_mutex_unlock(&mutex_workers);
157 //Update number of steps computed
166 * @function Force_Thread
167 * @purpose Thread - Calculates the forces on objects in a System
168 * @param s - Can be cast to the System*
170 void * Force_Thread(void * s)
173 System_Forces((System*)s, &universe); //Simple wrapper
175 pthread_mutex_lock(&mutex_workers);
176 workers_busy -= 1; // Count this thread as done
177 if (workers_busy == 0)
179 pthread_cond_signal(&workers_done_cv); // All threads done; wake up the compute_thread
181 pthread_mutex_unlock(&mutex_workers);
186 * @function Position_Thread
187 * @purpose Thread - Calculates the positions of objects in a System
188 * @param s - Can be cast to the System*
190 void * Position_Thread(void * s)
193 System_Positions((System*)s); // Simple wrapper
195 pthread_mutex_lock(&mutex_workers);
196 workers_busy -= 1; // Count this thread as done
197 if (workers_busy == 0)
199 pthread_cond_signal(&workers_done_cv); //All threads done; wake up the compute_thread
201 pthread_mutex_unlock(&mutex_workers);
206 * @function QuitProgram
207 * @purpose This function can either be called by the main thread in order to signal other threads
208 * that it wants to exit. The main thread then calls pthread_join before exiting.
209 * It can also be called by a child thread to request the main thread to exit.
210 * It is only used this way if there is an unrecovarable error (ie: Can't allocate memory in a child thread)
212 void QuitProgram(bool error)
214 if (runstate == QUIT || runstate == QUIT_ERROR)
215 return; //Don't do anything if already quitting
216 pthread_mutex_lock(&mutex_runstate); // aquire mutex
217 if (error) // set the runstate
218 runstate = QUIT_ERROR;
221 pthread_mutex_unlock(&mutex_runstate); //release mutex
225 * @function Thread_Cleanup
226 * @purpose Will be called in the main thread when exit() is called
227 * Automatically tells all other threads to quit (if they haven't already been told)
228 * Then waits for them to finish.
229 * Also frees memory associated with the worker threads.
231 void Thread_Cleanup(void)
233 if (runstate == RUN) // If this is true, as far as child threads are concerned, the simulation is still running
234 QuitProgram(false); // So call QuitProgram which will set runstate, and cause child threads to exit
235 pthread_join(compute_thread, NULL);
242 * @function Simulation_Run
243 * @purpose Initialise and start the simulation. Will be called in the main thread.
244 * Replaces the single-threaded macro that does nothing, and sets up the compute thread
245 * @param argc - Number of arguments - Passed to Graphics_Run if needed
246 * @param argv - Argument strings - Passed to Graphics_Run if needed
248 void Simulation_Run(int argc, char ** argv)
250 atexit(Thread_Cleanup);
252 if (options.draw_graphics)
254 // The graphics are enabled, so create a thread to do computations
255 // Graphics are done in the main loop
256 if (pthread_create(&compute_thread, NULL, Compute_Thread, (void*)&universe) != 0)
258 perror("Error creating compute thread");
261 Graphics_Run(argc, argv);
264 Compute_Thread((void*)(&universe)); // Graphics are disabled, so do computations in the main thread