In the CSP domain, the director creates a thread for executing each actor under its control. Each actor corresponds to a process in the model. The threads are created in the initialize method and started in the prefire method. After the thread for an actor is started it is active until the thread finishes. While the process is active, it can also be blocked or delayed, but not both. A process is blocked if it is trying to communicate but the process with which it is trying to communicate is not ready to do so yet. A process is delayed if it is waiting for time to advance, or if it is waiting for a deadlock to occur.
The director is responsible for handling deadlocks, both real and timed. It is also responsible for carrying out any requests for changes to the topology that have been made when a deadlock occurs. It maintains counts of the number of active processes, the number of blocked processes, and the number of delayed processes. Deadlock occurs when the number of blocked processes plus the number of delayed processes equals the number of active processes. Time deadlock occurs if at least one of the active processes is delayed. Real deadlock occurs if all of the active processes under the control of this director are blocked trying to communicate. The fire method controls and responds to deadlocks and carries out changes to the topology when it is appropriate.
If real deadlock occurs, the fire method returns. If there are no levels above this level in the hierarchy then this marks the end of execution of the model. The model execution is terminated by setting a flag in every receiver contained in actors controlled by this director. When a process tries to send or receive from a receiver with the terminated flag set, a TerminateProcessException is thrown which causes the actors execution thread to terminate.
Time is controlled by the director. Each process can delay for some delta time, and it will continue when the director has advanced time by that length of time from the current time. A process is delayed by calling delay(double) method. The director advances time each occasion a time deadlock occurs and no changes to the topology are pending. If a process specifies zero delay, then the process continues immediately. A process may delay itself until the next time deadlock occurs by calling waitForDeadlock(). Then the next occasion time deadlock occurs, the director wakes up any processes waiting for deadlock, and does not advance the current time. Otherwise the current model time is increased as well as being advanced. By default the model of computation used in the CSP domain is timed. To use CSP without a notion of time, do not use the delay(double) method in any process.
Changes to the topology can occur when deadlock, real or timed, is reached. The director carries out any changes that have been queued with it. Note that the result of the topology changes may remove the deadlock that caused the changes to be carried out.
@author Neil Smyth, Mudit Goel, John S. Davis II @version $Id: CSPDirector.java,v 1.145 2007/12/16 07:29:45 cxh Exp $ @since Ptolemy II 0.2 @Pt.ProposedRating Green (nsmyth) @Pt.AcceptedRating Green (kienhuis) @see ptolemy.actor.Director
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