Cleanup when `global.R` variables are deleted

Question

Question

From the documentation it is clear, that variables in server.R have a different life span than the ones in global.R.

For cleanup operations in server, there is the session$onSessionEnded callback function. An example to use this can be found here.

Is there something similar for the global.R script?

Context

In my setup, I have two variables with reference semantics (instances of R6 classes) in the global scope that need cleanup. The cleanup operation is dependend on both objects. Some pseudocode.

# context global.R
# -----------------------------------------------------------------------------------------

A = classA$new()
B = classB$new()

# call after the last sesion has ended
cleanupFunction = function(){
  # call this before B$finalize()
  A$saveToSQL(B)
  A$finalize()
}

A and B are both operaing on server.R.

---

Current workaround

Since both classA and classB are R6 classes, I have access to the finalize method (a destructor in C++ terms). So the following workaround is possible.

classA$finalize = function(){
  if(cleanupFlag){
    cleanupFunction()
    cleanupFlag <<- FALSE
  }
}

classB$finalize = function(){
  if(cleanupFlag){
    cleanupFunction()
    cleanupFlag <<- FALSE
  }
}

This requires me to use callbacks already because of scoping.

---

If someone knows a "proper" way to solve this, I would be very interested.