C++ future library Intorduction














































C++ future library Intorduction



Introduction Future Library

future is a class template and its object stores the future value,i.e...

A std::future object internally stores a value that will be assigned in future and it also provides a mechanism to access that value i.e. using get() member function. 
But if somebody tries to access this associated value of future through get() function before it is available, then get() function will block till value is not available.

The class template std::future provides a mechanism to access the result of asynchronous operations:

  • The creator of the asynchronous operation can then use a variety of methods to query, wait for, or extract a value from the std::future. These methods may block if the asynchronous operation has not yet provided a value.

future objects are only useful when they are valid(description below). Default-constructed future objects are not valid (unless move-assigned a valid future).

A valid future is a future object that is associated to a shared state, and are constructed by calling one of the following functions:
Few Member functions are:

  • constructor        Construct future 
  • destructor         Destroy future 
  • operator=         Move-assign future
  • share                Get shared future 
  • get                   Get value 
  • valid                 Check for valid shared state 
  • wait                  Wait for ready 
  • wait_for            Wait for ready during time span 
  • wait_until          Wait for ready until time point 
EXAMPLE CODE
// future example
#include <iostream>       
#include <future>         // std::async, std::future
#include <chrono>         // std::chrono::milliseconds

// a non-optimized way of checking for even numbers:
bool is_even(int x) {
  if (x%2!=0) return false;
  return true;
}

int main ()
{
  // call function asynchronously:
  std::future<bool> fut = std::async (is_even,100544443); 

  // do something while waiting for function to set future:
  std::cout << "checking, please wait";
  std::chrono::milliseconds span (100);
  while (fut.wait_for(span)==std::future_status::timeout)
    std::cout << '.' << std::flush;

  bool x = fut.get();     // retrieve return value

  std::cout << "\n100544443 " << (x?"is":"is not") << " even.\n";

  return 0;
}
OUTPUT

checking, please wait...........
1005444443 is not even



More Articles of Harshit Jain:

Name Views Likes
C++ Ranges::all_view, begin, cbegin Introduction 454 1
C++ future library Intorduction 576 1
C++ Ranges :: ViewableRange, ref_view, reverse_view 536 1
Threads Stop_token library C++ 593 1
C++ cfenv(Numerics Library) Introduction 424 1
YAML CPP Introduction 3599 1
Thead Library C++ Introduction 386 1
Introduction to gSOAP library 554 1
C++ ranges::ForwardRange, InputRange, OutputRange Introduction 566 1
Shared Mutex C++ Introduction 2038 1
SEMAPHORE HEADER C++(MULTI_THREADING) Introduction 1739 1
C++ Ranges::dangling, sized_range, disable_sized range Introduction 357 1
C++ Ranges::views::empty, filter, reverse, iota and Ranges::iota_view Introduction 593 1
MyCSS ( a CSS parser ) Introduction 370 1
C++ ranges::view::VIEW, ALL, COUNTED Introductiion 434 1
Mutex Locks C++ Multithreading Introduction 595 1
C++ Ranges:: Range, RandomAccessRange Introduction 359 1
Condition Variable(Multithreading) C++ Introduction 1724 1
Cpp - toml++ introduction 417 1
C++ Ranges::iterator_t, safe_iterator_t, safe_subrange_t Introduction 278 1
C++ Ranges::empty_view , enable_view, filter_view Introduction 462 1
C++ Barriers(Multithreading) Introduction 2321 1
LATCHES C++ Introduction 791 1
C++ Ranges::bidirectional_range, commom_range, contiguous range Introduction 360 1
C++ ZeroMQ - Introduction 1843 1
C++ BIT Library Introduction 374 1

Comments