The lpIdle flag

The lpIdle flag in the LogicalProcess class is defined as an instance of OneShot<bool> type. The template class OneShot<class foo> instantiates a foo internally and mimics the foo class in all respects; all of the operators are defined to operate just like the foo's operators. However, the class OneShot adds two methods to the foo class, called reset and didItChange. When the method didItChange is invoked, it returns a boolean whose value indicates whether or not its value has changed since the last time reset was accessed. Once a new value is assigned to the foo instantiated inside the OneShot, didItChange will return true until reset is called again - hence the name OneShot.

The lpIdle is used to indicate when the LogicalProcess is completely idle. The definition of completely idle for an LP is that

• All of its simulation objects are idle. For a simulation object to be idle, it has to have no unprocessed events in its queue.
• The GVTManager has no messages that it is waiting for acknowledgment on. This means that GVTManager::needAcked.size == 0.

Since it is impossible for the LP to know if any messages for it are in transit, these conditions are sufficient only to tell if it is idle. The problem of determining if the entire simulation is idle is discussed in the section on termination.