3.1.12. Consistency with MPI

The removal or addition of a task that is a boundary task should be reflected in the nbor list of nbors that are virtual tasks, and there could possibly be a signficant delay before that happens. The sequence of events should be:

• A thread always sends a boundary task to rank nbors, after updating or creating it. At that time, a bit (bits%init_nbors) must be set, which triggers the receiving rank to update the nbor lists of the task; either creating it if is a new task, or removing it and the task, if the task is to be removed.
  • So, when should an init_nbors() call be made from task_mesg_t%unpack? Clearly, when a new task is being created, but also when a task that is an nbor is removed or one that should become one is created. The first type causes a call automatically (should it?), while the 2nd type is triggered by the bits%init_nbors being set.
  • The first type occurs when a task has just been created by AMR, and for a boundary task it happens both on the owner rank and on virtual nbor ranks.
• As a consequnce of that, all nbors of that (virtual) task on the rank nbor should also have their nbor lists renewed. This includes those boundary tasks that appear as virtual tasks on the first rank.
• As the nbor lists of those virtual tasks are being modified, they thread that is doing the modifications must, correspondinly, take the appropriate action (i.e. calling check_nbors() for new tasks, as well as for tasks that are being removed.