The program can be compiled with the following command:

g++ main.cpp -lpthread

As you can see, we need to link the POSIX pthread library dynamically.

Check out the following screenshot and visualize the output of the multithreaded program:

The code that is written in ThreadProc runs within the thread context. The preceding program has a total of four threads, including the main thread. I had blocked the main thread with pthread_join to force it to wait for the other three threads to complete their tasks first, failing which the main thread would have exited before them. When the main thread exits, the application exits too, which ends up prematurely destroying newly created threads.

Though we created thread1, thread2, and thread3 in the respective sequence, there is no guarantee that they will be started in the exact same sequence they were created in.

The operating system scheduler decides the sequence in which the threads must be started, based on the algorithm used by the operating system scheduler. Interestingly, the sequence in which the threads get started might vary at different runs in the same system.