====== C - C++ Threads - Troubleshooting - Program Crashes - Forgetting to join a thread ======

Forgetting to join a thread or detach it (make it unjoinable) before the main program terminates, will cause in a program crash.

For example, the t1 thread is not joined to the main thread.

<code cpp>
#include <iostream>
#include <thread>
using namespace std;


void HelloWorld()
{
  cout << "Hello World" << endl;
}


int main()
{
  thread t1(HelloWorld);
  //t1.join();  // If the thread is not joined to the main thread it will cause a crash.
  return 0;
}
</code>

<WRAP info>
**NOTE:**  Why does it crash ??? 

  * This is because, at the end of the main function, thread t1 goes out of scope and the thread destructor is called.
  * Inside the destructor, a check is performed to see if thread t1 is joinable.
  * A joinable thread is a thread that has not been detached.
  * If the thread is joinable, std::terminate is called.
</WRAP>


----

===== Resolution =====

There are two ways to fix this depending on your needs.

==== 1.  Join the thread t1 to the main thread ====

<code cpp>
int main()
{
  thread t1(HelloWorld);
  t1.join();  // Join t1 to the main thread.
  return 0;
}
</code>

----

==== 2. Detach the thread t1 from the main thread and let it continue as a daemon thread ====

<code cpp>
int main()
{
  thread t1(HelloWorld);
  t1.detach();  // Detach t1 from main thread.
  return 0;
}
</code>

----