printtask.h

// Fig. 17.3: printtask.h
// Function printTask defines a task to perform in a separate thread.
#include <chrono>
#include <fmt/format.h> 
#include <iostream>
#include <sstream>
#include <string>
#include <thread>

// get current thread's ID as a string
std::string id() {
    std::ostringstream out;
    out << std::this_thread::get_id();
    return out.str();
}

// task to perform in a separate thread 
void printTask(const std::string& name, 
   std::chrono::milliseconds sleepTime) {

   // <chrono> library features we'll use for timing
   using std::chrono::steady_clock;
   using std::chrono::duration_cast;
   using std::chrono::milliseconds;

   std::cout << fmt::format("{} (ID {}) going to sleep for {} ms\n",
      name, id(), sleepTime.count());

   auto startTime{steady_clock::now()}; // get current time

   // put thread to sleep for sleepTime milliseconds 
   std::this_thread::sleep_for(sleepTime); 

   auto endTime{steady_clock::now()}; // get current time
   auto time{duration_cast<milliseconds>(endTime - startTime)};
   auto difference{duration_cast<milliseconds>(time - sleepTime)};
   std::cout << fmt::format("{} (ID {}) awakens after {} ms ({} + {})\n",
      name, id(), time.count(), sleepTime.count(), difference.count());
}


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