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Embedded Programming with Modern C++

- Example

Explore how std async calls work in C++ multithreading by comparing lazy and eager execution. Understand how futures trigger asynchronous tasks and affect timing. This lesson enables you to control task execution and synchronization for multiple threads effectively.

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Example

C++
// asyncLazyEager.cpp
#include <chrono>
#include <future>
#include <iostream>
int main(){
  std::cout << std::endl;
  auto begin= std::chrono::system_clock::now();
  auto asyncLazy=std::async(std::launch::deferred,
                            []{ return std::chrono::system_clock::now(); });
  auto asyncEager=std::async(std::launch::async,
                             []{ return std::chrono::system_clock::now(); });
  std::this_thread::sleep_for(std::chrono::seconds(1));
  auto lazyStart= asyncLazy.get() - begin;
  auto eagerStart= asyncEager.get() - begin;
  auto lazyDuration= std::chrono::duration<double>(lazyStart).count();
  auto eagerDuration=  std::chrono::duration<double>(eagerStart).count();
  std::cout << "asyncLazy evaluated after : " << lazyDuration 
            << " seconds." << std::endl;
  std::cout << "asyncEager evaluated after: " << eagerDuration 
            << " seconds." << std::endl;
  std::cout << std::endl;
}

Explanation

  • Both std::async calls (at lines 13 and 16) return the current time point. The first call is ...