Thanks for clarifying how the dangling pointers may arise. Not everyone agrees with me, but these are my thoughts/recommendations when using Ada. Which thread/task that has ownership of a variable is paramount. Whenever one defines a variable it must be crystal clear which thread/task that owns it, for example has the right the read or write a value to the variable. What I recommend is the Actor Model (https://en.wikipedia.org/wiki/Actor_model). Synchronization between two tasks can either be through shared variables or message passing. Last time I checked Academia is inconclusive as to what is the best (least error-prone) way for threads/tasks to communicate. What seems the simplest to me is message passing. 10 years ago, first time I heard of the Actor Model and message passing is Erlang and it's a language where these ideas are fundamental. So a task owns a variable. If another task wishes to change the value of that variable it must send a message to the owning task and request it to change the value. If another task wishes to know the value it must ask the owning task what the value is. Since the time I heard of Erlang, other languages like Rust and the Pony language has picked up on this too. Rust has taken this further by making it possible for one task to temporarily borrow ownership to another task and it is checked by the borrow-checker.
To implement the Actor Model in Ada one puts all variables in the body of the tasks that are in the application. It makes them not visible from other tasks. So what you need to keep in mind when developing is for a task to never send an access-to-object type variable to another task. If there is a need to do that you need to use Ada/SPARK or Rust to get the proper ownership checking done. Btw, Codepeer (static code analysis tool for Ada) finds race-conditions, has deadlock detection, and warns if there are variables that may be read or written to by more than one task.
If one sticks to vanilla Ada (not SPARK) one could develop an application based on libadalang that parses all the Ada source code and checks that all task entries have input arguments that do not contain any access-to-object types (to find instances where a developer has sent an access-to-object variable to another task by mistake). Such a tool does not exist but libadalang exists to allow the creation of custom rules checking on one's Ada code.
To implement the Actor Model in Ada one puts all variables in the body of the tasks that are in the application. It makes them not visible from other tasks. So what you need to keep in mind when developing is for a task to never send an access-to-object type variable to another task. If there is a need to do that you need to use Ada/SPARK or Rust to get the proper ownership checking done. Btw, Codepeer (static code analysis tool for Ada) finds race-conditions, has deadlock detection, and warns if there are variables that may be read or written to by more than one task.
If one sticks to vanilla Ada (not SPARK) one could develop an application based on libadalang that parses all the Ada source code and checks that all task entries have input arguments that do not contain any access-to-object types (to find instances where a developer has sent an access-to-object variable to another task by mistake). Such a tool does not exist but libadalang exists to allow the creation of custom rules checking on one's Ada code.