boost::thread_group in C++11?

Question

Is there anything like boost::thread_group in C++11?

I'm just trying to port my program from using boost:thread to C++11 threads and wasn't able to find anything equivalent.

Slacken

Boost threads and C++11 threads are different. I personally keep using boost threads because of the more complete API (and the lack of current implementation of eg. thread local storage). – Detachment

Answer 1

No, there's nothing directly equivalent to boost::thread_group in C++11. You could use a std::vector<std::thread> if all you want is a container. You can then use either the new for syntax or std::for_each to call join() on each element, or whatever.

Plummer

Since 2012 has there been a better solution to this problem? – Potheen

I'd like to add that there is really no magic in boost::thread_group, it's a little more than a vector of threads (the "little more" being some utility functions like join_all and create_thread). – Egarton

Answer 2

thread_group didn't make it into C++11, C++14, C++17 or C++20 standards.

But a workaround is simple:

  std::vector<std::thread> grp;

  // to create threads
  grp.emplace_back(functor); // pass in the argument of std::thread()

  void join_all() {
    for (auto& thread : grp)
        thread.join();
  }

Not even worth wrapping in a class (but is certainly possible).

Minicam

Answer 3

If you have access to C++20, then you can use std::vector and std::jthread instead of std::thread to create a group of threads.

If you use std::jthread then no need to call join() on each thread. jthread automatically calls join() upon destruction.

Here is a working example:

https://godbolt.org/z/o9rPfd4zn

#include <iostream>
#include <thread>
#include <vector>

int main()
{
    constexpr int count = 3;
    std::vector<std::jthread> thread_group;

    for( int i = 1; i <= count; ++i )
    {
        thread_group.emplace_back([i=i](){ 
            std::this_thread::sleep_for(std::chrono::seconds(i)); 
            std::cout << " Thread " << i << " finished." << std::endl;
            });
    }
    // no need to join the threads here
}

Lian