implementation of asynchronous thread in c++ - c++

Question

I am unable to find a correct usage of asynchronous thread in c++11.The thing i want to do is i want to spwan threads and each thread will function simultaneously without waiting for each other like thread.join(),which makes other thread to wait until the current thread is done with.So,is there any library in c++ which makes threads to run parallely doing their work simultaneously without having to wait for the other to complete.Actually the thing i want is i want to run each threads sumultaneously, so that they don't wait for the other to complete and its functionality is executed simultaneously without having to wait for others to finish .
Thanks,
Kushal
EDIT:
EDIT:: i am posting the code below
#include <signal.h>
#include <thread>
#include <algorithm>
#include <cstring>
#include <csignal>
#include "paho_client.h"
using namespace std;
vector<string> topic_container{"rpi2/temp","sense /bannana","sense/util","mqtt/temp","sense/temp","sense/pine","sense/fortis/udap"};
vector<paho_client> publisher;
vector<paho_client> subscriber;
int finish_thread=1;
void Onfinish(int signum){
finish_thread=0;
exit(EXIT_FAILURE);
}
int main(int argc, char** argv) {
signal(SIGINT, Onfinish);
int topic_index;
if(argc<3){
cout<<"the format of starting commandline argument is"<<endl;
exit(1);
}
while(finish_thread!=0){
//paho_client::get_library_handle();
if(strcmp(argv[1],"create_publisher")){
for(topic_index=0;topic_index<atoi(argv[2]);topic_index++){
thread pub_th;
pub_th = thread([ = ]() {
paho_client client("publisher", "192.168.0.102", "9876",
topic_container[topic_index].c_str());
client.paho_connect_withpub();
publisher.push_back(client);
});
pub_th.join();
}
vector<paho_client>::iterator it;
int publisher_traverse=0;
for(it=publisher.begin();it<publisher.end();publisher_traverse++){
publisher[publisher_traverse].increment_count();
publisher[publisher_traverse].get_count();
}
}
}
return 0;
}
After using async with future am getting the same behaviour as above please point me where am i going wrong
#include <signal.h>
#include <thread>
#include <algorithm>
#include <cstring>
#include <csignal>
#include <future>
#include "paho_client.h"
using namespace std;
vector<string> topic_container{"rpi2/temp","sense/apple","sense/bannana","sense/util","mqtt/temp","sense/temp","sense/pine","sense/fortis/udap"};
vector<paho_client> publisher;
vector<paho_client> subscriber;
int finish_thread=1;
void Onfinish(int signum){
finish_thread=0;
exit(EXIT_FAILURE);
}
int accumulate_block_worker_ret(int topic_index) {
//int topic_index=0;
paho_client client("publisher", "192.168.0.102", "9876",
topic_container[topic_index].c_str());
client.paho_connect_withpub();
publisher.push_back(client);
client.increment_count();
return client.get_count();
}
int main(int argc, char** argv) {
signal(SIGINT, Onfinish);
if(argc<3){
cout<<"the format of starting commandline argument is . /paho_client_emulate <create_publisher><count of publisher client to spawn>" <<endl;
exit(1);
}
while(finish_thread!=0){
// paho_client::get_library_handle();
int topic_index;
if(strcmp(argv[1],"create_publisher")){
for(topic_index=0;topic_index<atoi(argv[2]);topic_index++){
// thread pub_th;
// pub_th = thread([ = ]() {
future<int> f = async(std::launch::async,accumulate_block_worker_ret,topic_index);
// });
// pub_th.join();
cout<<"the returned value from future is"<<f.get()<<endl;
}
vector<paho_client>::iterator it;
int publisher_traverse=0;
for(it=publisher.begin();it<=publisher.end();publisher_traverse++){
cout<<"came here"<<endl;
publisher[publisher_traverse].increment_count();
publisher[publisher_traverse].get_count();
}
}
}
return 0;
}

Answer 1

i want to launch all the publisher clients first (as threads) and
later publish messages from each threads
The pub_th.join() is misplaced inside the loop where the threads are started, thus waiting for the termination of each thread before starting the next one. To let the threads run in parallel, just move the .join() outside that loop. Of course to access the threads after the loop body, they have to be stored somewhere, e. g. in a vector - for this, change the first for loop to
vector <thread> pub_threads;
for (topic_index=0; topic_index<atoi(argv[2]); topic_index++)
{
pub_threads.push_back(thread([ = ]() { /* whatever */ }));
}
and later when done:
for (auto &th: pub_threads) th.join();
Actually i am running infinite while inside every instance of
paho_client so the first thread is not completed …
that thread is run continously
Of course if never done, there's no point to .join().