src/pthreads/src/test_atomic.cpp

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#include <pthread.h>

#include <atomic>
#include <cstdlib>
#include <iostream>

//------------------------------------------------------------------------
// Create n threads, run them in parallel and wait for them in the master
// thread.
// Each child thread increments a shared variable m times atomically
//------------------------------------------------------------------------

#define MAX_N_WORKER_THREADS 10

typedef struct
{
    int nsteps;
    std::atomic<int>* shared_var;
} ThreadArg;

void* func( void* args )
{
    ThreadArg* my_args = ( ThreadArg* ) args;

    int nsteps = my_args->nsteps;
    std::atomic<int>* shared_var = my_args->shared_var;

    for ( int i = 0; i < nsteps; ++i ) {
        std::atomic_fetch_add(shared_var, 1);
    }

    return nullptr;
}

int main( int argc, const char* argv[] )
{
    int n_worker_threads = 0;

    // allocate all threads
    pthread_t* threads = new pthread_t[MAX_N_WORKER_THREADS];

    // variable shared among all threads
    std::atomic<int> shared_var(0);

    // number of steps each thread increments the shared_var
    int nsteps = 1000;

    // set up threads' arguments
    ThreadArg* t_args = new ThreadArg[MAX_N_WORKER_THREADS];

    int ret = 0;
    for ( size_t tid = 0; tid < MAX_N_WORKER_THREADS; tid++ ){
        t_args[tid].nsteps = nsteps;
        t_args[tid].shared_var = &shared_var;

        // spawn thread
        ret = pthread_create( threads + tid, nullptr, func, &t_args[tid] );

        if (ret != 0) {
            break;
        }

        n_worker_threads++;
    }

    // sync up all threads
    for ( int tid = 0; tid < n_worker_threads; ++tid ) {
        pthread_join( threads[tid], nullptr );
    }

    // clean up
    delete[] threads;
    delete[] t_args;

    // verify
    if ( shared_var != n_worker_threads * nsteps || n_worker_threads < 1)
        return EXIT_FAILURE;

    return EXIT_SUCCESS;
}