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std::jthread::joinable

From cppreference.com
< cpp‎ | thread‎ | jthread
 
 
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[[nodiscard]] bool joinable() const noexcept;
(since C++20)

Checks if the std::jthread object identifies an active thread of execution. Specifically, returns true if get_id() != std::jthread::id(). So a default constructed jthread 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.

Contents

[edit] Parameters

(none)

[edit] Return value

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

[edit] Example

#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::jthread t;
    std::cout << "before starting, joinable: " << t.joinable() << '\n';
 
    t = std::jthread{foo};
    std::cout << "after starting, joinable: " << t.joinable() << '\n';
 
    t.join();
    std::cout << "after joining, joinable: " << t.joinable() << '\n';
 
    t = std::jthread{foo};
    t.detach();
    std::cout << "after detaching, joinable: " << t.joinable() << '\n';
 
}

Output:

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

[edit] References

  • C++23 standard (ISO/IEC 14882:2023):
  • 33.4.4.3 Members [thread.jthread.mem]
  • C++20 standard (ISO/IEC 14882:2020):
  • 32.4.3.2 Members [thread.jthread.mem]

[edit] See also

returns the id of the thread
(public member function) [edit]
waits for the thread to finish its execution
(public member function) [edit]
permits the thread to execute independently from the thread handle
(public member function) [edit]