std::thread::joinable (3) Linux Manual Page

std::thread::joinable – std::thread::joinable

Synopsis

bool joinable() const noexcept; (since C++11)
Checks if the 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

See also

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

References

* C++11 standard (ISO/IEC 14882:2011):

      * 30.3.1.5 thread members [thread.thread.member]