/*
 
 File: executions.c of Dispatch_Compared
 
 Abstract: Compare overhead of several GCD approaches with that of serial code and threads
 
 Version: 1.0
 
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*/

#include "executions.h"
#include "benchmark.h"

#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <math.h>
#include <assert.h>
#include <pthread.h>
#include <dispatch/dispatch.h>

static double *results = NULL;
static int n_folds = 1;

// Perform relatively complex trigonometry on the input value, and store in a (uniquely indexed) global array
void work_function(int i)
{
    double x = 1.0+i*i; // zero would skew the result
    for (int j=0; j < n_folds; ++j) {
        x = tan(M_PI_2 - atan(exp(2*log(sqrt(x))))); // really slow identity function
    }
    if (NULL != results) results[i] = x;
}


// The thread entry point routine.
void* PosixThreadMainRoutine(void* data)
{
    int* iptr = data;
    work_function(*iptr);
    return NULL;
}

// Create threads using POSIX routines, then wait for them to finish.
// Note: this is NOT the most efficient way to use threads, but rather an example of 'naive' parallelism
void* UseThread(int n)
{
    pthread_t thread_id[n];
    int index[n];
    
    for (int i = 0; i < n; i++) {
        index[i] = i;
        int threadError = pthread_create(&thread_id[i], NULL, PosixThreadMainRoutine, (void *) &index[i]);
        assert(threadError == 0);
    }   
    for (int i = 0; i < n; i++) {
        int threadError = pthread_join(thread_id[i], NULL);
        assert(threadError == 0);
    }
#ifdef DEBUG
    fprintf(stderr, "\tRan %d threads\n", n);
#endif
    return NULL;
}

// Use many queues -- this is also inefficient :-)

void* UseMultiQueue(int n)
{
    dispatch_queue_t queues[n];
    char *queue_label;
    for (int i = 0; i < n; i++) {
        int rc = asprintf(&queue_label, "com.apple.gcd.examples.compare.multiq%04d", i);
        assert(rc > 0);
        queues[i] = dispatch_queue_create(queue_label, NULL);
        free(queue_label);
        assert(queues[i] != NULL);
        dispatch_async(queues[i], ^{
            work_function(i);
        });
    }
    for (int i = 0; i < n; i++) {
        dispatch_sync(queues[i], ^{ }); // block until queue has completed all previous work
        dispatch_release(queues[i]);
    }
    return NULL;
}

// Use dispatch groups to queue concurrently, then wait for completion
void* UseConcurrentQueue(int n)
{
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0);
    dispatch_group_t group = dispatch_group_create();
    assert(group);
    
    for (int i = 0; i < n; i++) {
        dispatch_group_async(group, queue, ^{
            work_function(i);
        });
    }
    dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
    dispatch_release(group);
    return NULL;
}

// Use a private serial queue.
void* UseSerialQueue(int n)
{
    dispatch_queue_t queue = dispatch_queue_create("com.apple.gcd.examples.compare.serial", NULL);
    assert(queue);
    
    for (int i = 0; i < n; i++) {
        dispatch_async(queue, ^{
            work_function(i);
        });
    }
    dispatch_sync(queue, ^{ return; }); // block until queue has completed all previous work
    dispatch_release(queue);
    return NULL;
}

// Use the highly optimized dispatch_apply to loop concurrently.
void* UseApply(int n)
{
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0);
    dispatch_apply(n, queue, ^(size_t i){
        work_function(i);
    });
    return NULL;
}

void* UseOpenMP(int n)
{
#pragma omp parallel for    
    for (int i = 0; i < n; i++) {
        work_function(i);
    }
    return NULL;
}

// Run calculation entirely in the main thread; least overhead but zero parallelism.
void* UseLoop(int n)
{
    for (int i = 0; i < n; i++) {
        work_function(i);
    }
    return NULL;
}

// External Functions

void executions_setup(int max_iterations, int folds)
{
    results = (double*)malloc(max_iterations*sizeof(double));
    n_folds = folds;
}

void executions_run(int i)
{
    benchmark_header(i);
    benchmark_function(i, "loop", UseLoop, NULL);
    benchmark_function(i, "apply", UseApply, NULL);
    benchmark_function(i, "serial", UseSerialQueue, NULL);
    benchmark_function(i, "parallel", UseConcurrentQueue, NULL);
    benchmark_function(i, "queues", UseMultiQueue, NULL);
    benchmark_function(i, "openmp", UseOpenMP, NULL);
    if (i < 1e4)
        benchmark_function(i, "thread", UseThread, NULL);
}

void executions_done(int n)
{
    if (NULL != results) return;

    printf("Calculation results:\n");
    for (int i = 0; i < n; i++) {
        if (results[i] != 0)
            printf("  %'10.0f", results[i]);
    }
    printf("\n\tdone.\n");
    free(results);
}