W3cubDocs

/C++

std::thread::join

void join();
(since C++11)

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

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";
}

Output:

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

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

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/thread/thread/join