NAME

std::thread::joinable - std::thread::joinable

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)

Return value

true if the thread object identifies an active thread of execution, false otherwise

Example

// Run this code

#include <iostream>
#include <thread>
#include <chrono>

void foo()
{
std::this_thread::sleep_for(std::chrono::seconds(1));
}

int main()
{
std::thread t;
std::cout << "before starting, joinable: " << std::boolalpha << 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';
}

Output:

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

References

* 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]