std::jthread::joinable

 

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std::jthread

Member functions

jthread::jthread

jthread::~jthread

jthread::operator=

Observers

jthread::joinable

jthread::get_id

jthread::native_handle

jthread::hardware_concurrency

Operations

jthread::join

jthread::detach

jthread::swap

Stop token handling

jthread::get_stop_source

jthread::get_stop_token

jthread::request_stop

Non-member functions

swap(std::jthread)

 

[[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.

Parameters

(none)

Return value

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

Example

Run this code

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

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]

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)