The Petri Net in Figure 2d models a group of n concurrent processes in a shared

The petri net in figure 2d models a group of n

This preview shows page 13 - 15 out of 96 pages.

Problem 5.The Petri Net in Figure 2(d), models a group ofnconcurrent processes in ashared-memory environment. At any given time only one process may write, but any subsetof thenprocesses may read at the same time, provided that no process writes. Identify thefiring sequences, the markings of the net, the postsets of all transitions and the presets of allplaces. Can you construct a state machine to model the same process? (10) and in this state both read and write operations are permitted. When transition t 2 fires - this represents the initialization of a write request - then the marking becomes M 1 = ( n 1 , 0 , 1 , 0) (11) and neither transition t 1 - which represents the initialization of a read request - nor t 2 can fire, as place p 2 contains no token. This means that only one process can write at a time and no process can read during the write operation. After transition t 3 fires - this represents the actual write operation - the marking becomes the initial one, M 0 . When the system is in state represented by marking M 0 and transition t 1 fires - this represents the initialization of a read request - then the marking becomes M 1 = ( n 1 , n 1 , 0 , 1) (12) and transition t 2 cannot fire - no write can be initialized, but successive n 1 reads can be initiated and then completed. From the state represented by marking M 1 there are two possibilities: 13
Image of page 13
t 4 ( a ) ( b ) ( c ) p 4 t 3 n n n n ( d ) p 1 p 1 p 1 p 1 p 2 p 2 p 2 p 3 p 2 p 3 p 3 p 3 t 1 t 1 t 1 t 1 p 4 p 4 p 4 t 2 t 2 t 2 t 2 t 3 t 3 t 4 t 4 Figure 2: (a) A state machine; there is the choice of firing t 1 , or t 2 ; only one transition fires at any given time, concurrency is not possible. (b) A marked graph can model concurrency but not choice; transitions t 2 and t 3 are concurrent, there is no causal relationship between them. (c) An extended net used to model priorities; the arc from p 2 to t 1 is an inhibitor arc.
Image of page 14
Image of page 15

You've reached the end of your free preview.

Want to read all 96 pages?

  • Summer '17
  • The Land, cloud service, Cloud delivery models, Cloud Computing delivery

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes