std::jthread::join

void join();		(since C++20)

Blocks the current thread until the thread identified by *this finishes its execution.

The completion of the thread identified by *this synchronizes with the corresponding successful return from join().

No synchronization is performed on *this itself. Concurrently calling join() on the same jthread object from multiple threads constitutes a data race that results in undefined behavior.

Parameters

(none)

Return value

(none)

Postconditions

joinable() is false

Exceptions

std::system_error if an error occurs.

Error Conditions

resource_deadlock_would_occur if this->get_id() == std::this_thread::get_id() (deadlock detected)
no_such_process if the thread is not valid
invalid_argument if joinable() is false

Example

Run this code

#include <iostream>
#include <thread>
#include <chrono>
 
void foo()
{
    // simulate expensive operation
    std::this_thread::sleep_for(std::chrono::seconds(1));
}
 
void bar()
{
    // simulate expensive operation
    std::this_thread::sleep_for(std::chrono::seconds(1));
}
 
int main()
{
    std::cout << "starting first helper...\n";
    std::jthread helper1(foo);
 
    std::cout << "starting second helper...\n";
    std::jthread helper2(bar);
 
    std::cout << "waiting for helpers to finish..." << std::endl;
    helper1.join();
    helper2.join();
 
    std::cout << "done!\n";
}

Output:

starting first helper...
starting second helper...
waiting for helpers to finish...
done!

Language
Standard Library Headers
Freestanding and hosted implementations
Named requirements
Language support library
Concepts library (C++20)
Diagnostics library
Utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications

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)

detach	permits the thread to execute independently from the thread handle (public member function)
joinable	checks whether the thread is joinable, i.e. potentially running in parallel context (public member function)