Avoiding deadlocks with std::scoped_lock
If deadlocks had occurred in road traffic, they would have looked like the following situation:
In order to get the traffic flow going again, we either need a large crane that randomly picks one car from the center of the street intersection and removes it. If that is not possible, then we need enough drivers to be cooperative. The deadlock can be solved by all drivers in one direction driving several meters backwards, making space for the other drivers to continue.
In multithreaded programs, such situations, of course, need to be avoided strictly by the programmer. It is however too easy to fail in that regard when the program is really complex.
In this recipe, we are going to write code which intentionally provokes a deadlock situation. Then we will see how to write code that acquires the same resources that led the other code into a deadlock, but use the new STL lock class std::scoped_lock that came with C++17, in order to avoid this mistake.
