Examples of ptolemy.domains.dde.kernel.PrioritizedTimedQueue$Event

• org.oasis.wsrp.v2.Event
  A FIFO queue with time and priority attributes that is used for storing tokens with time stamps. A "time stamp" is a time value that is associated with a token and is used to order the consumption of a token with respect to other time stamped tokens. To help organize the tokens contained by this queue, two flags are maintained: last time and receiver time. The last time flag is defined to be equivalent to the time stamp of the token that was most recently placed in the queue. The receiver time flag is defined as the time stamp of the oldest token in the queue or the last token to be removed from the queue if the queue is empty. Both of these flags must have monotonically, non-decreasing values (with the exception of the IGNORE, INACTIVE and ETERNITY values). At the conclusion of a simulation run the receiver time is set to INACTIVE.

  A PrioritizedTimedQueue is subclassed by DDEReceiver. Hence, PrioritizedTimedQueues serve as the foundation for receivers contained in the IO ports of actors operating within DDE models. A TimeKeeper object is assigned to each actor that operates according to the DDE model of computation. The TimeKeeper manages each of the receivers that are contained by an actor by keeping track of the receiver times of each receiver. As information flows through a PrioritizedTimedQueue, the TimeKeeper must be kept up to date with respect to the receiver times. The TimeKeeper orders the PrioritizedTimedQueues according to their receiver times and priorities. PrioritizedTimedQueues with smaller receiver times are ordered first.

  PrioritizedTimedQueues with identical receiver times are sorted according to their respective priorities. PrioritizedTimedQueues are assigned priorities (a nonnegative integer) by a TimeKeeper when the TimeKeeper is instantiated. Receivers with higher receiver priorities are ordered before receivers with lower priorities. The priority of a receiver can be explicitly specified or it can be implicitly determined based on the topology. In the latter case, the priority of a receiver is set according to the inverse order in which it was connected to the model topology. I.e., if two input receivers (receiver A and receiver B) are added to an actor such that receiver A is connected in the model topology before receiver B, then receiver B will have a higher priority than receiver A.

  If the oldest token in the queue has a time stamp of IGNORE, then the next oldest token from the other receivers contained by the actor in question will be consumed and the token time stamped IGNORE will be dropped. The IGNORE time stamp is useful in feedback topologies in which an actor should ignore inputs from a feedback cycle when the execution of the model is just beginning. FeedBackDelay actors output a single IGNORE token during their initialize() methods for just this reason. In general, IGNORE tokens should not be handled unless fundamental changes to the DDE kernel are intended.

  The values of the package friendly variables IGNORE, INACTIVE and ETERNITY are arbitrary as long as they have unique, negative values. ETERNITY is used in conjunction with the completionTime to indicate that an actor should continue executing indefinitely.

  Note that a PrioritizedTimedQueue is intended for use within a multi-threaded environment. PrioritizedTimedQueue does not require the synchronization facilities provided by ptolemy.kernel.util.Workspace. PrioritizedTimedQueue is subclassed by DDEReceiver which adds significant synchronization facilities and where appropriate employs workspace. @author John S. Davis II @version $Id: PrioritizedTimedQueue.java,v 1.53 2007/12/06 18:22:00 cxh Exp $ @since Ptolemy II 0.4 @Pt.ProposedRating Green (davisj) @Pt.AcceptedRating Green (kienhuis) @see ptolemy.domains.dde.kernel.DDEReceiver @see ptolemy.domains.dde.kernel.TimeKeeper

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