Executing functions asynchronously

Threads enable us to run multiple functions at the same time; this helps us take advantage of the hardware facilities in multiprocessor or multicore systems. However, threads require explicit, lower-level operations. An alternative to threads is tasks, which are units of work that run in a particular thread. The C++ standard does not provide a complete task library, but it enables developers to execute functions asynchronously on different threads and communicate results back through a promise-future channel, as seen in the previous recipe. In this recipe, we will see how to do this using std::async() and std::future.

Getting ready

For the examples in this recipe, we will use the following functions:

void do_something()
{
  // simulate long running operation
  {
    using namespace std::chrono_literals;
    std::this_thread::sleep_for(2s);
  } 
  std::lock_guard<std::mutex> lock(g_mutex);
  std::cout << "operation 1 done...