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Execution Model

The RT++ model of program execution can be sketched as follows:

• A number of processes executes threads from the ready queue. Thread execution is preemptive i.e. after a certain time slice has elapsed, each process puts the currently executed thread back into the ready queue and selects a new thread for execution.
• A ready queue contains all active threads i.e. all threads that are immediately ready for execution (and that may have been previously under execution). Active threads are fairly scheduled for execution on a first in/first out basis.
• A lazy stack contains all threads that are in principle ready for execution but that still need to be activated before they can be actually executed. Lazy threads are activated on a last in/first out basis only if an idle process finds the ready queue empty.
• A heap contains all data structures on which the threads operate. Each thread can access each entity in the heap regardless by which process it is currently executed.