CSPActor
ptolemy.domains.csp.kernel.CSPActor

This class is the base class of all atomic actors using the non-deterministic communication and timed features of the communicating sequential processes(CSP) domain. <p> Two conditional communication constructs are available: "Conditional if" (CIF) and "Conditional do" (CDO). The constructs are analogous to, but different from, the common <I>if</I> and <I>do</I> statements. The steps involved in using both of these are <BR>(1) create the branches involved and assign an identification number to each branch. <BR>(2) call the chooseBranch() method, which invokes the chooseBranch() method of the controller to determine which branch should succeed. <BR>(3) execute the statements associated with the successful branch. <P> Each branch is either an instance of ConditionalSend or ConditionalReceive, depending on the communication in the branch. Please see these classes for details on <I>guarded communication statements</I>, which they represent. The identification number assigned to each branch only needs to identify the branch uniquely for one sequence of the steps above. A good example of how to use a CDO is the code in the actor CSPBuffer, in the ptolemy.domains.csp.lib package. One significant difference between a CDO (or CIF) and a common <I>do</I> (<I>if</I>) is that all the branches are evaluated in parallel, as opposed to sequentially. <p>The chooseBranch() method takes an array of the branches as an argument, and simply passes the branches to the chooseBranch() method of the controller to decide which branch is successful. The successful branch is the branch that succeeds with its communication. See the chooseBranch() method of ConditionalBranchController for details about how the successful branch is chosen. <p>Time is supported by the method delay(double). This delays the process until time has advanced the argument time from the current model time. If this method is called with a zero argument, then the process continues immediately. As far as each process is concerned, time can only increase while the process is blocked trying to rendezvous or when it is delayed. A process can be aware of the current model time, but it should only affect the model time through delays. Thus time is centralized in that it is advanced by the director controlling the process represented by this actor. <p>A process can also choose to delay its execution until the next occasion a deadlock occurs by calling _waitForDeadlock(). The process resumes at the same model time at which it delayed. This is useful if a process wishes to delay itself until some changes to the topology have been carried out. <p> The model of computation used in this domain extends the original CSP, as proposed by Hoare in 1978, model of computation in two ways. First it allows non-deterministic communication using both sends and receives. The original model only allowed non-deterministic receives. Second, a centralized notion of time has been added. The original proposal was untimed. Neither of these extensions are new, but it is worth noting the differences between the model used here and the original model. If an actor wishes to use either non-deterministic rendezvous or time, it must derive from this class. Otherwise deriving from AtomicActor is sufficient. <p>

Author(s): Neil Smyth, Bilung Lee
Version:$Id: CSPActor.doc.html,v 1.1 2006/02/22 18:40:26 mangal Exp $
Pt.Proposed Rating:Green (nsmyth)
Pt.Accepted Rating:Yellow (liuj)