std::thread::joinable(3)

💅 std::thread::joinable 💅

okay so this is the std::thread::joinable(3) page from the C++ Standard Libary manual — yes bestie, that's the manual name folded in right here, and we're not copying the header line, we're giving it main character energy instead. It's a tiny baddie of a page, and it's lowkey important. Let's go. 🦋

🎀 NAME 🎀

std::thread::joinable — std::thread::joinable.

That's the name section doing its little mirror thing, and honestly? iconic. It's the std::thread::joinable member function, no notes. 💅

✨ Synopsis ✨

bool joinable() const noexcept;  (since C++11)

Checks if the std::thread object identifies an active thread of execution.

Specifically, returns true if get_id() != std::thread::id(). So a default constructed thread is not joinable.

A thread that has finished executing code, but has not yet been joined is still considered an active thread of execution and is therefore joinable.

🫶 Parameters 🫶

(none) — literally no parameters, not a single one. The parameters section is empty and living its best life. 🫶

🌈 Return value 🌈

true if the thread object identifies an active thread of execution, false otherwise. That's the whole vibe check. ✅

🍓 Example 🍓

The page says // Run this code, so run it, bestie:

#include <chrono>
#include <iostream>
#include <thread>
using namespace std::chrono_literals;

void foo()
{
    std::this_thread::sleep_for(500ms);
}

int main()
{
    std::cout << std::boolalpha;

    std::thread t;
    std::cout << "before starting, joinable: " << t.joinable() << '\n';

    t = std::thread{foo};
    std::cout << "after starting, joinable: " << t.joinable() << '\n';

    t.join();
    std::cout << "after joining, joinable: " << t.joinable() << '\n';

    t = std::thread{foo};
    t.detach();
    std::cout << "after detaching, joinable: " << t.joinable() << '\n';
    std::this_thread::sleep_for(1500ms);
}

💖 Output 💖

before starting, joinable: false
after starting, joinable: true
after joining, joinable: false
after detaching, joinable: false

👑 References 👑

• C++23 standard (ISO/IEC 14882:2023):
  • 33.4.3.6 Members [thread.thread.member]
• C++20 standard (ISO/IEC 14882:2020):
  • 32.4.2.5 Members [thread.thread.member]
• C++17 standard (ISO/IEC 14882:2017):
  • 33.3.2.5 thread members [thread.thread.member]
• C++14 standard (ISO/IEC 14882:2014):
  • 30.3.1.5 thread members [thread.thread.member]
• C++11 standard (ISO/IEC 14882:2011):
  • 30.3.1.5 thread members [thread.thread.member]

🦋 See also 🦋

• get_id — returns the id of the thread (public member function).
• join — waits for the thread to finish its execution (public member function).
• detach — permits the thread to execute independently from the thread handle (public member function).

mwah 💋 this lil page is from http://cppreference.com, dated 2024.06.10, and it's the std::thread::joinable(3) page — source, version, date, all mentioned, periodt. 💖