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114 | // Copyright 2021 Jeisson Hidalgo-Cespedes <jeisson.hidalgo@ucr.ac.cr> CC-BY-4
// Creates an arbitrary amount of threads that greet in stdout
#include <assert.h>
#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
typedef struct {
size_t thread_count;
size_t next_thread;
} shared_data_t;
typedef struct {
size_t thread_number;
shared_data_t* shared_data;
} private_data_t;
int create_threads(shared_data_t* shared_data);
void* run(void* data);
int main(int argc, char* argv[]) {
int error = EXIT_SUCCESS;
shared_data_t* shared_data = (shared_data_t*)
calloc(1, sizeof(shared_data_t));
if (shared_data) {
shared_data->next_thread = 0;
shared_data->thread_count = sysconf(_SC_NPROCESSORS_ONLN);
if (argc == 2) {
if (sscanf(argv[1], "%zu", &shared_data->thread_count) != 1 || errno) {
fprintf(stderr, "error: invalid thread count\n");
return EXIT_FAILURE;
}
}
struct timespec start_time;
clock_gettime(/*clk_id*/CLOCK_MONOTONIC, &start_time);
error = create_threads(shared_data);
struct timespec finish_time;
clock_gettime(/*clk_id*/CLOCK_MONOTONIC, &finish_time);
double elapsed = (finish_time.tv_sec - start_time.tv_sec) +
(finish_time.tv_nsec - start_time.tv_nsec) * 1e-9;
printf("execution time: %.9lfs\n", elapsed);
free(shared_data);
}
return error;
}
int create_threads(shared_data_t* shared_data) {
assert(shared_data);
int error = EXIT_SUCCESS;
pthread_t* threads = (pthread_t*) calloc(shared_data->thread_count
, sizeof(pthread_t));
private_data_t* private_data = (private_data_t*)
calloc(shared_data->thread_count, sizeof(private_data_t));
if (threads && private_data) {
for (size_t index = 0; index < shared_data->thread_count; ++index) {
private_data[index].thread_number = index;
private_data[index].shared_data = shared_data;
if (pthread_create(&threads[index], /*attr*/ NULL, run
, &private_data[index]) == EXIT_SUCCESS) {
} else {
fprintf(stderr, "error: could not create thread %zu\n", index);
error = 21;
break;
}
}
printf("Hello from main thread\n");
for (size_t index = 0; index < shared_data->thread_count; ++index) {
pthread_join(threads[index], /*value_ptr*/ NULL);
}
free(threads);
free(private_data);
} else {
fprintf(stderr, "error: could not allocate memory for %zu threads\n"
, shared_data->thread_count);
error = 22;
}
return error;
}
void* run(void* data) {
const private_data_t* private_data = (private_data_t*)data;
const size_t my_thread_id = private_data->thread_number;
const size_t thread_count = private_data->shared_data->thread_count;
// Wait until it is my turn
while (private_data->shared_data->next_thread < my_thread_id) {
// busy-waiting
}
// Do the ordered-task here
printf("Hello from secondary thread %zu of %zu\n", my_thread_id
, thread_count);
// Allow subsequent thread to do the task
++private_data->shared_data->next_thread;
return NULL;
}
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