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Modeling Process

Modeling Process. proposed facility. May be several algorithms (processes) runs on each processor to simulate the desired communication system. For example, a processor run two algorithms (processes) at the same time one process (algorithm) that uses the broadcast service

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Modeling Process

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  1. Modeling Process proposed facility Set 14: Simulations • May be several algorithms (processes) runs on each processor to simulate the desired communication system. • For example, a processor run two algorithms (processes) at the same time • one process (algorithm) that uses the broadcast service • another process (algorithm) that implements the asynchronous broadcast system on top of the asynchronous point-to-point message-passing system

  2. Modeling Process (Cont.) Algorithm composition • Ordering of process, forming a “Stack of protocols” • Environment communicates with the top layer • Each process uses communication primitives to interact with the layer beneath it • The bottom layer communicates with the Communication System Set 14: Simulations

  3. modeled as a problem spec (interface & allowable sequences) layer 1 layer 2 layer 3 communicate via appropriate primitives: shared events modeled as a problem spec (interface & allowable sequences) Simulation for Modeling Process environment modeled as state machines communication system Set 14: Simulations Layered model

  4. layer 1 layer 2 layer 3 Simulation for Modeling Process (Cont.) environment Send Send Send Send communication system Set 14: Simulations Propagation of events

  5. Modeling Process Specifications (1) • A system consists of • A collection of n processors (or nodes), p0 through pn-1 • A communication system C linking the nodes • Environment E • Notes • Environment E and Communication system C are given as problem specifications • Node is a hardware notion • Running on each node are one or more processes • Processes are organized into a single stack of layers • The same number of layers on each node Set 14: Simulations

  6. Modeling Process Specifications (2) • Each process is state machine (modeled as an automaton) • Has a set of states, including a subset of initial states • Has hour kinds of events • Inputs coming in from the layer above (or the environment, if this is the top layer) • Outputs going out to the layer above • Inputs coming in from the layer below (or the communication system, if this is the bottom layer) • Outputs going out to the layer below • Events of type 1 and 2 form the top interface of the process • Events of type 3 and 4 form the bottom interface of the process Set 14: Simulations

  7. layer i - 1 layer i layer i + 1 Top interface of layer i 1 2 Bottom interface of layer i 4 3 Set 14: Simulations Propagation of events

  8. Modeling Process Specifications (3) • Events • Concepts • An event is said to be enabled in a state of a process if there is a transition from that state labeled with that event • Inputs from the environment and from the communication system are called node inputs • A configuration of the system specifies a state for every process on every node • A configuration does not include the state of the communication system • An initial configuration contains all initial states

  9. Modeling Process Specifications (4) • An execution of the system is a sequence C0 e1 C1 e2 C2 … of alternating configurations Ciand events ei • If it is finite, ending with a configuration • Satisfies the following conditions • Configuration C0 is an initial configuration

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