El problema es sincronizar n número de subprocesos utilizando la biblioteca pthread. La idea es tomar el número de hilos e imprimir 1 en el primer hilo, imprimir 2 en el segundo hilo, imprimir 3 en el tercer hilo, ….. imprimir n en el enésimo hilo y nuevamente repetir desde el hilo 1 infinitamente.
Requisito previo: subprocesamiento múltiple
Ejemplos:
Input : Thread count Output : 1 2 3 ... thread count 1 2 3 ... thread count 1 2 3 ... thread count .... Input : 5 Output : 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 ....
A continuación se muestra la implementación:
CPP
// C code to synchronize threads
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t* cond = NULL;
int threads;
volatile int cnt = 0;
// function to synchronize threads
void* foo(void* arg)
{
// turn is a basically to identify a thread
int turn = *(int*)arg;
while (1) {
pthread_mutex_lock(&mutex);
// cnt is used to determine which thread should
// enter into critical section(printf() statement)
if (turn != cnt) {
// put all thread except one thread in waiting
// state
pthread_cond_wait(&cond[turn], &mutex);
}
// it's a time to print turn can have
// values starting from 0. Hence + 1
printf("%d ", turn + 1);
// determine which thread need to be scheduled now
if (cnt < threads - 1) {
cnt++;
}
else {
cnt = 0;
}
// wake up next thread
pthread_cond_signal(&cond[cnt]);
pthread_mutex_unlock(&mutex);
}
return NULL;
}
// Driver code
int main()
{
pthread_t* tid;
volatile int i;
int* arr;
printf("\nEnter number of threads: ");
scanf("%d", &threads);
// allocate memory to cond (conditional variable),
// thread id's and array of size threads
cond = (pthread_cond_t*)malloc(sizeof(pthread_cond_t)
* threads);
tid = (pthread_t*)malloc(sizeof(pthread_t) * threads);
arr = (int*)malloc(sizeof(int) * threads);
// Initialize cond (conditional variable)
for (int i = 0; i < threads; i++) {
if (pthread_cond_init(&cond[i], NULL) != 0) {
perror("pthread_cond_init() error");
exit(1);
}
}
// create threads
for (i = 0; i < threads; i++) {
arr[i] = i;
pthread_create(&tid[i], NULL, foo, (void*)&arr[i]);
}
// waiting for thread
for (i = 0; i < threads; i++) {
pthread_join(tid[i], NULL);
}
return 0;
}
Producción :
