std::thread::join

void join();

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 thread 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

#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::thread helper1(foo);
 
    std::cout << "starting second helper...\n";
    std::thread helper2(bar);
 
    std::cout << "waiting for helpers to finish..." << std::endl;
    helper1.join();
    helper2.join();
 
    std::cout << "done!\n";
}

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

References

• C++23 standard (ISO/IEC 14882:2023):
• 33.4.3.6 Members [thread.thread.member]
• 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]

See also