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--- c:c_threads:troubleshooting:program_crashes:forgetting_to_join_a_thread [2021/06/07 08:58] – created peter
+++ c:c_threads:troubleshooting:program_crashes:forgetting_to_join_a_thread [2021/06/07 08:58] (current) – peter
@@ Line 1: / Line 1: @@
 ====== 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>
+----