Parallel Programming - Finished OpenMP

[matches/honours.git] / course / semester2 / pprog / assignment1 / mthread / nbody.c~

/**
 * @file nbody.c
 * @purpose Implentation of multi-threaded N-Body simulator using pthreads
 * @author Sam Moore (20503628) - 2012
 */

#include "nbody.h" // Declarations
#include "../single-thread/nbody.c" // Include all functions from the single threaded version
#include <assert.h>
#include "graphics.h" // For declaration of Graphics_Run only
#include "barrier.c"

// --- Variable declarations --- //

pthread_t compute_thread; // The thread responsible for computations; it spawns worker threads (* terms and conditions apply)
        
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
System * nested_sub_system = NULL; //Array of Systems for division of "universe" for the nested worker threads

pthread_mutex_t mutex_runstate; // Mutex around the runstate




Barrier force_barrier; // I laughed at this variable name. A bit sad really.
Barrier position_barrier;


Barrier graphics_barrier;

pthread_mutex_t mutex_threads_running;
int threads_running = 0;

/**
 * @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 
 *
 *      NOTE:
 *      This will always be (void*)(&universe) where universe is the global System variable that has every Body in it.
 *      But I don't like global variables. And since the argument had to be passed, I thought I might as well use it.
 *      That way, when I change "universe" to "solar_system", I only have to change the argument where this is called, not all through it.
 *      Find and replace? Who uses that!?
 */


void * Compute_Thread(void * arg)
{

        System * s = (System*)(arg); //cast argument to a System*



        // If no number of threads provided, use the default value, unless someone (me) changed that to a stupid value
        if (options.num_threads <= 0)
                options.num_threads = (DEFAULT_WORKING_THREADS > 1) ? DEFAULT_WORKING_THREADS : 1; // Fear the ternary operator!

        if (options.nested_threads <= 0)
                options.nested_threads = 1;

        // Do a sanity check; there is no point spawning more threads than bodies.
        if (options.num_threads > s->N)
        {
                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;
        }

        // Initialise the barriers ("shields up!")
        Barrier_Init(&force_barrier, options.num_threads);
        Barrier_Init(&position_barrier, options.num_threads);
        Barrier_Init(&graphics_barrier, 1);

        
        
        if (options.num_threads > 1) // If we require additional worker threads...
        {
                // Allocate worker threads and sub systems
                
                sub_system = Split_System(&universe, options.num_threads);

                if (options.nested_threads > 1)
                        nested_sub_system = Split_System(&universe, options.nested_threads);

                #ifdef PERSISTENT_THREADS // Code for the smart way of doing it (spawn threads once, keep them running)
                worker_thread = Allocate_Threads(options.num_threads-1);
                // Spawn a bunch of worker threads, and let them all do their thing.
                // Note the "-1". Because this thread can do work too!
                for (unsigned i = 0; i < options.num_threads-1; ++i)
                {
                        if (pthread_create(worker_thread+i, NULL, Worker_Thread, (void*)(sub_system+i)) != 0)
                        {
                                perror("In compute thread, couldn't create worker thread");
                                QuitProgram(true);
                                pthread_exit(NULL);
                        }
                }
                Worker_Thread((void*)(sub_system+options.num_threads-1)); // This thread becomes a worker thread
                #else
                worker_thread = Allocate_Threads(options.num_threads);
                #endif //PERSISTENT_THREADS
                
        }
        #ifdef PERSISTENT_THREADS
        else // We only require one worker thread...
        {
                // So just do all computations in this thread
                while (!ExitCondition())
                {
                        
                        System_Forces(s, s);
                        // If required, wait for graphics to finish drawing
                        if (options.draw_graphics && options.pedantic_graphics)
                                Barrier_Wait(&graphics_barrier);
                        System_Positions(s);
                        StepFunction(s);

                        if (options.draw_graphics && options.pedantic_graphics)
                                Barrier_ForceExit(&position_barrier); //Make the graphics continue
                }
                QuitProgram(false);
                pthread_exit(NULL);
        }

        #else // Code for the stupid way of doing it (respawn threads each step)
                // (ie: The way I immediately implemented and didn't realise was stupid until someone told me)


        

        // Run until we can't run anymore
        while (!ExitCondition())
        {
                

                if (options.num_threads <= 1) // If there is only 1 worker thread...
                {
                        // Just do everything in this thread 
                        System_Forces(s, s);
                        // If required, wait for graphics to finish drawing
                        if (options.draw_graphics && options.pedantic_graphics)
                                Barrier_Join(&graphics_barrier);

                        System_Positions(s);
                        StepFunction(s);

                        if (options.draw_graphics && options.pedantic_graphics)
                                Barrier_Join(&position_barrier); //Make the graphics continue
                        continue;
                }

                

                //Compute forces by spawning threads, each thread gets a sub system
                for (unsigned i = 0; i < options.num_threads; ++i)
                {
                        if (pthread_create(worker_thread+i, NULL, Force_Thread, (void*)(sub_system+i)) != 0)
                        {
                                perror("In compute thread, couldn't create worker thread (force)");
                                QuitProgram(true);
                                pthread_exit(NULL);
                        }       
                                
                }

                for (unsigned i = 0; i < options.num_threads; ++i)
                        pthread_join(worker_thread[i], NULL);

                
                // If required, wait for graphics to finish drawing
                if (options.draw_graphics && options.pedantic_graphics)
                        Barrier_Wait(&graphics_barrier);


                Barrier_Enter(&position_barrier);

                //Compute positions by spawning a bunch of threads to do it
                for (unsigned i = 0; i < options.num_threads; ++i)
                {
                        if (pthread_create(worker_thread+i, NULL, Position_Thread, (void*)(sub_system+i)) != 0)
                        {
                                perror("In compute thread, couldn't create worker thread (position)");
                                QuitProgram(true);
                                pthread_exit(NULL);
                        }       
                }

                
                for (unsigned i = 0; i < options.num_threads; ++i)
                        pthread_join(worker_thread[i], NULL);


                StepFunction(s); // Execute single threaded stuff
                

        }
        QuitProgram(false);
        #endif //PERSISTENT_THREADS
        return NULL;
}

/**
 * @function BeforeDraw
 * @purpose Called in graphics thread before the draw loop
 *      When --pedantic-graphics enabled, will wait for position computations to finish before drawing
 *      Otherwise does nothing
 *
 *      This originally seemed like a good place to put the code now in StepFunction(), since only one thread runs this
 *      But then I realised that the graphics might be disabled, 
 *              and there was no point having a thread that only existed to call that code.
 *
 *      So I changed it to the horrible solution that I currently have.
 */
void BeforeDraw()
{
        
        //printf("BEFORE DRAW\n");
        if (!options.pedantic_graphics)
                return;
        
        //printf("Graphics thread waits on position barrier\n");
        Barrier_Wait(&position_barrier);        
        //printf("\tGraphics thread wakes up\n");
        Barrier_Enter(&graphics_barrier);
}

/**
 * @function AfterDraw
 * @purpose Called in graphics thread after the draw loop
 *      When --pedantic-graphics is supplied, will signal computation threads that drawing is finished
 *              So that positions can be safely altered
 *      Otherwise does nothing
 */
void AfterDraw()
{
        //universe.steps += 1;
        if (!options.pedantic_graphics)
                return;
        Barrier_Join(&graphics_barrier);
        
}

#ifdef PERSISTENT_THREADS

/**
 * @function Worker_Thread
 * @purpose Thread - A self contained worker thread to compute a particular sub system of bodies
 *
 * This is the "smart" way to do it, because threads are only created once, and compute both force and position.
 * The greatest difficulty with pthreads is getting a *single* thread from the team to execute certain code
 *      (ie: The stuff in StepFunction()).
 * With the "continuously respawning threads of stupidity" approach, 
 * because there is one "master" thread (not necessarilly the main thread... don't get confused now)
 *      to keep respawning the workers, the single threaded code can just be executed in the master thread.
 *
 * With this approach, I have created a hacky solution so that the *last* thread to leave the position barrier gets to call StepFunction.
 *      
 */
void * Worker_Thread(void * arg)
{
        System * s = (System*)(arg); // This is mainly to save typing the RHS a lot of times

        // Each thread runs until the whole program is supposed to end
        while (!ExitCondition()) 
        {
                
        
                System_Forces(s, &universe); // Each thread computes the forces for its share of bodies

                // Do not confuse with "Barrier_Wait".
                // Barrier_Wait does not affect the barrier; it just waits for it
                // Barrier_Join actively updates the state of the barrier, and wakes up sleeping threads if required.

                Barrier_Join(&force_barrier); // All threads must reach here before moving on.
                if (ExitCondition()) return NULL;

                
                //fprintf(stderr,"Thread %p - force barrier finished\n", arg);
                //printf("Computed ALL forces\n");

        
                // If required, wait for the graphics to finish drawing stuff
                if (options.draw_graphics && options.pedantic_graphics)
                {
                        //printf("Worker %p waits on graphics barrier\n", arg);
                        Barrier_Wait(&graphics_barrier);
                        //printf("\tWorker %p wakes up after graphics barrier\n", arg);
                        if (ExitCondition()) return NULL;
                }
                

                
                Barrier_Enter(&position_barrier);
                System_Positions(s); // Each thread updates the positions for its share of bodies


                // Barrier_JoinCall behaves in the same way as Barrier_Join, except the *last* thread 
                //      (ie: the one that wakes up the others) also calls the function with arguments given.
                Barrier_JoinCall(&position_barrier, StepFunction, (void*)(&universe));
                if (ExitCondition()) return NULL;
                //Barrier_Join(&position_barrier);

                // All threads have computed positions, and *one* thread calls StepFunction()
                
        }
        QuitProgram(false); // Set the run state of the program
        return NULL;
}

#endif //PERSISTENT_THREADS

/**
 * @function Force_Thread
 * @purpose Thread - Calculates the forces on objects in a System
 * @param s - Can be cast to the System*
 */
void * Force_Thread(void * s)
{
        //System_ForcePair * pair = (System_ForcePair*)s;

        
        System_Forces(s, &universe); //Simple wrapper
        //printf("Force_Thread waits\n");

        return NULL;
}


/**
 * @function Position_Thread
 * @purpose Thread - Calculates the positions of objects in a System 
 * @param s - Can be cast to the System*
 */
void * Position_Thread(void * s)
{

        System_Positions((System*)s); // Simple wrapper
        Barrier_Join(&position_barrier); // This needed so that graphics will wait

        return NULL;
}       

/**
 * @function QuitProgram
 * @purpose This function can be called in any thread to signal all threads to exit
 *      Repeated calls to this function have no effect
 *
 *      All threads periodically call ExitCondition(), which will return true if the program should exit.
 *              One (not the only way) to return true is if this function has been called.
 *      Threads will call this function if they detect ExitCondition() is true. Only the first call has any effect.
 */
inline void QuitProgram(bool error)
{
        //If already quitting, don't do anything
        if (runstate == QUIT || runstate == QUIT_ERROR) 
                return; 

        

        // set the runstate (checked in ExitCondition())

        pthread_mutex_lock(&mutex_runstate); // aquire mutex
        if (error) 
                runstate = QUIT_ERROR; // Program is exiting due to an error
        else
                runstate = QUIT; // Program is exiting naturally
        pthread_mutex_unlock(&mutex_runstate); //release mutex

        
}

/**
 * @function Thread_Cleanup
 * @purpose Will be called in the *main* thread when exit() is called
 *      Ensures working threads will exit, and waits for them to finish.
 *      Then waits for them to finish.
 *      Also frees memory associated with the worker threads.   
 */
void Thread_Cleanup(void)
{
        

        // Threads recheck the exit condition whenever they leave a barrier.
        // These calls will stop any threads waiting forever in a barrier for threads that exited before getting to the barrier.
        Barrier_ForceExit(&force_barrier); 
        Barrier_ForceExit(&position_barrier);


        if (options.draw_graphics) // If the graphics are enabled...
        {
                // Then there is a computation thread, since graphics are done in the main thread
                pthread_join(compute_thread, NULL); 
        }

        #ifdef PERSISTENT_THREADS
                for (unsigned i = 0; i < options.num_threads-1; ++i)
                {
                        pthread_join(worker_thread[i], NULL);
                }
        #else 
                // All other worker threads (if they were spawned) are terminated in Compute_Thread
        #endif //PERSISTENT_THREADS

        // Scary memory management here.
        if (worker_thread != NULL)
                free(worker_thread);
        if (sub_system != NULL)
                free(sub_system);
        worker_thread = NULL;
        sub_system = NULL;

}


/**
 * @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 graphics and computation threads
 * @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
        {
                // I have chosen to do graphics in the main thread in this case.
                // A *single* seperate thread is spawned here to do computations.
                // This computation thread will spawn any additional worker threads required.
                if (pthread_create(&compute_thread, NULL, Compute_Thread, (void*)&universe) != 0)
                {
                        perror("Error creating compute thread");
                        exit(EXIT_FAILURE);
                }

                // This is run in the main thread
                // It is effectively the graphics initialisation, followed by the glut loop
                Graphics_Run(argc, argv);

                // The main thread reaches here after leaving the glut loop when ExitCondition() returns true.

                QuitProgram(false);

                exit(EXIT_SUCCESS); // This is the main thread; use exit()
                
        }
        else //The graphics are disabled
        {
                // If graphics are disabled, there is no point spawning an extra thread.
                // In this case, the *main* thread starts computations.
                // Note that it will probably spawn additional worker threads (unless options.num_threads <= 1)
                Compute_Thread((void*)(&universe));
                QuitProgram(false);
                exit(EXIT_SUCCESS);
        }
}





/**
 * @function Allocate_Threads
 * @purpose Helper function to allocate an array of pthread_t objects
 *      Handles all the pointless, er, "important" error checking that should be done
 * @param n - Number of threads in the array
 * 
 * WARNING: Remember to free() the array!!!
 */
pthread_t * Allocate_Threads(unsigned n)
{
        pthread_t * result = (pthread_t*)(calloc(n, sizeof(pthread_t)));
        if (result == NULL)
        {
                perror("Unable to allocate memory for threads");
                QuitProgram(true);
                pthread_exit(NULL);
        }
        return result;
}

/**
 * @function StepFunction
 * @purpose Helper to perform stuff in a single thread every step, after position computations are done
 *      The reason this has void* all over the place is so that I can pass the function pointer (to horrible dragons and fiendish demons).
 * @param arg - Can be cast to System* for which steps are to be updated
 *      Will always be (void*)(&universe). But I have been brainwashed into the "global variables are baaaaad" philosophy.
 * @returns arg
 */
void * StepFunction(void * arg)
{
        //fprintf(stderr, "StepFunction called\n");
        System * s = (System*)(arg);
        s->steps += 1; //Increment number of steps computed

        if (options.verbosity != 0 && s->steps % options.verbosity == 1)
                DisplayStatistics();


        return arg;
}