how thread is implemented in c++

user_12659494 0
Viewed 211
#include <pthread.h>
#include <iostream>
#include <iomanip>

#define NOPER 4

struct operation
{
    int val1;
    int val2;
    int op;
    double result;
};

void *calculator(void *pos_void_ptr)
{
    struct operation *pos_ptr = (struct operation *)pos_void_ptr;
    switch(pos_ptr->op)
    {
        case 0: pos_ptr->result = pos_ptr->val1 + pos_ptr->val2; 
                break;
        case 1: pos_ptr->result = pos_ptr->val1 - pos_ptr->val2; 
                break;
        case 2: pos_ptr->result = pos_ptr->val1 * pos_ptr->val2; 
                break;
        case 3: if (pos_ptr->val2 != 0)
                    pos_ptr->result = (double) pos_ptr->val1 / pos_ptr->val2; 
                else
                    pos_ptr->result = 0;         
                break;
    }
    return NULL;
}

int main()
{
    static struct operation operations[NOPER];
    pthread_t tid[NOPER];

    for(int i=0;i<NOPER;i++)
    {
        operations[i].op = i;
        std::cin >> operations[i].val1;
        std::cin >> operations[i].val2;
        if(pthread_create(&tid[i], NULL, calculator, &operations[i])) 
        {
            fprintf(stderr, "Error creating thread\n");
            return 1;

        }       
    }
    // Wait for the other threads to finish.
    for (int i = 0; i < NOPER; i++)
            pthread_join(tid[i], NULL);
    for (int i = 0; i < NOPER; i++)
    {
        switch(operations[i].op)
        {
            case 0: std::cout << operations[i].val1 << " + " << operations[i].val2 << " = " << std::fixed << std::setprecision(2) << operations[i].result << std::endl;
                    break;
            case 1: std::cout << operations[i].val1 << " - " << operations[i].val2 << " = " << std::fixed << std::setprecision(2) << operations[i].result << std::endl;
                    break;
            case 2: std::cout << operations[i].val1 << " * " << operations[i].val2 << " = " << std::fixed << std::setprecision(2) << operations[i].result << std::endl;
                    break;
            case 3: std::cout << operations[i].val1 << " / " << operations[i].val2 << " = " << std::fixed << std::setprecision(2) << operations[i].result << std::endl;
                    break;
        }
    }
    return 0;
}

I am trying to have the basic idea about what goes inside the 

void *calculator(void *pos_void_ptr)
    {
        struct operation *pos_ptr = (struct operation *)pos_void_ptr;
        switch(pos_ptr->op)

and what are these parameters in the

(pthread_create(&tid[i], NULL, calculator, &operations[i])

and how to implement this in any program? this program takes 2 inputs 4 times and it add the first 2 elements then multiply the second 2 elements then subtract the third 2 elements then divide the fourth 2 elements

pthreads c++
1 Answers

Here you define 4 thread identifiers that you'll later pass to pthread_create:

pthread_t tid[NOPER];

Then you create 4 threads:

pthread_create(&tid[i], NULL, calculator, &operations[i])

First argument is the pthread_t identifier, second one is an optional attribute parameter of type pthread_attr_t that can be initialized with pthread_attr_init function, third one is the name of the function that the new thread will execute, and fourth one is the parameter(s) for the function passed as 3rd argument.

In the calculator function you basically cast a void pointer parameter to an operation struct and switch on its op field to determine whether to add, subtract, multiply, or divide.

user_137070950
Related