multi-thread sample

thread.cpp

/**
MacOS : clang++ -std=c++17 -stdlib=libc++ -O2 sample.cpp
GCC:    g++ -std=c++17 -lpthread sample.cpp

constrains resource in docker : docker run -it --rm --name=thread --cpuset-cpus="3" gcc bash
**/
#include <iostream>
#include <sstream>
#include <vector>
#include <pthread.h> // POSIX
#include <sched.h>
#include <unistd.h>

using namespace std;
double pi(uint64_t n) {
    double sum = 0.0;
    uint64_t sign = 1;
    for (uint64_t i = 0; i < n; ++i) {           
        sum += sign/(2.0*i+1.0);
        sign *= -1;
    }
    return 4.0*sum;
}
// invoke from a thread
void* callee(void* m) {
    string out = static_cast<char *>(m);

    int num = sysconf(_SC_NPROCESSORS_CONF);
    printf("system has %d processor(s)\n", num);

    
    istringstream iss(out);
    vector<string> ve;
    string tmp;

    while(getline(iss, tmp, ',')) {
        ve.emplace_back(tmp);
    }
    
    printf("Launch %s by a thread\n", ve[0].c_str());
    cout << pi(stoll(ve[1])) << "from " << ve[0] << endl;
    printf("Done %s by a thread\n", out.c_str());
    

    return nullptr;
}

int main() {
    pthread_t t1, t2;
    pthread_attr_t attr;
    sched_param param;

    // sched_priority value in the range 1(low) to 99(high)
    pthread_attr_init (&attr);
    pthread_attr_getschedparam (&attr, &param);
    printf("current priority : %d\n", param.sched_priority);
    param.sched_priority = 99;
    pthread_attr_setschedparam(&attr, &param);

    pthread_create(&t1, nullptr, callee, (void *) "#1,100000000000");
    sleep(3);
    pthread_create(&t2, &attr, callee, (void *) "#2,10000000");
    
    pthread_join(t1, nullptr);
    pthread_join(t2, nullptr);
    
    return 0;
}