A guarded accept clause only executes (i.e., processes a message)  if a specific condition is true.

Message passing would work well on a distributed memory MIMD system but would not work properly on a shared memory MIMD machine.

Message passing can model a Monitor if it stores a data structure within a task and provides accept clauses to access the data structure

In an Ada select/or clause, if there are multiple non-empty accept queues, Ada will run the first one listed in the source code.

A task executes its own accept clauses concurrently