The following code example is taken from the book
The C++ Standard Library - A Tutorial and Reference, 2nd Edition
by Nicolai M. Josuttis, Addison Wesley Longman, 2012
Copyright © 2012 by Pearson Education, Inc. and Nicolai M. Josuttis
#include <future>
#include <thread>
#include <chrono>
#include <random>
#include <iostream>
#include <exception>
using namespace std;
void doSomething (char c)
{
// random-number generator (use c as seed to get different sequences)
default_random_engine dre(c);
uniform_int_distribution<int> id(10,1000);
// loop to print character after a random period of time
for (int i=0; i<10; ++i) {
this_thread::sleep_for(chrono::milliseconds(id(dre)));
cout.put(c).flush();
}
}
int main()
{
cout << "starting 2 operations asynchronously" << endl;
// start two loops in the background printing characters . or +
auto f1 = async([]{ doSomething('.'); });
auto f2 = async([]{ doSomething('+'); });
// if at least one of the background tasks is running
if (f1.wait_for(chrono::seconds(0)) != future_status::deferred ||
f2.wait_for(chrono::seconds(0)) != future_status::deferred) {
// poll until at least one of the loops finished
while (f1.wait_for(chrono::seconds(0)) != future_status::ready &&
f2.wait_for(chrono::seconds(0)) != future_status::ready) {
//...;
this_thread::yield(); // hint to reschedule to the next thread
}
}
cout.put('\n').flush();
// wait for all loops to be finished and process any exception
try {
f1.get();
f2.get();
}
catch (const exception& e) {
cout << "\nEXCEPTION: " << e.what() << endl;
}
cout << "\ndone" << endl;
}