ch.3

Question 1

what is the difference between concurrency and parallel processing

Answer 1

• concurrency: the ability to handle multiple activities simultaneously
• parallel processing: the ability to handle multiple activities concurrently. aims to shorten the completion time

Question 2

what all concurrent activities should have and why it’s important?

Answer 2

• All concurrent activities should have coordination and it’s very important because without it it could lead to deadlocks
• they should have communication because that leads to enhancing the overall efficiency of the concurrent activities

Question 3

give an example of a coordination (synchronization) problem.

Answer 3

Dining Philosophers problem

Question 4

explain dining philosophers’ problem

Answer 4

• Five philosophers want to eat on a table
• Only five chopsticks are available on the table
• Each philosopher needs two chopsticks to be able to eat
• Without synchronization could lead to deadlock

Question 5

what is the solution to the dining philosophers’ problem?

Answer 5

the solution is Dijkstra’s solution which is:
* assign the resources by order
* each philosopher will request chopsticks with an order
* philosophers will request the lower-numbered chopstick first and cannot order two at the same time
This solution avoids starvation

Question 6

what is the speed-up in concurrency in the cloud

Answer 6

through concurrent execution to overcome the physical limitations of one computer so the process is divided into multiple processes to speed up the process

Question 7

what are the two sides of concurrency

Answer 7

• algorithmic or logical concurrency
• physical concurrency
  For example: a compiler can optimize a sequential program, but a processor core can execute many programs concurrently

Question 8

What is barrier synchronization?

Answer 8

when concurrently running tasks cannot continue to the next stage until all tasks finished

Question 9

What do you know about?
communication and computation

Answer 9

• communication is much slower than computation
• intensive communication can drastically slow the computation of concurrent threads of applications

Question 10

what is the difference between coarse-grained and fine-grained parallelism?

Answer 10

• coarse-grained: execute large blocks of code before communication
• fine-grained: execute small blocks of code before communication
  Fine-grained is not suitable for the cloud because it will slow it

Question 11

what is the difference between data parallelism and task parallelism?

Answer 11

• Data parallelism: data is distributed across different concurrent activities.
• Task parallelism: tasks are distributed across multiple processors.

Question 12

what is the difference between data-flow and control-flow

Answer 12

data-flow: threads start execution as soon as their input becomes available

Question 13

what is better data-flow or control-flow and why?

Answer 13

data-flow is better because the word is divided automatically. and the execution also starts automatically when inputs are available. So, it’s better because it can have the highest benefit from concurrency

Question 14

What do you know about?
BSP bulk synchronous parallel model

Answer 14

• it manages the concurrent activities
• it makes parameter tuning on every physical constraint
• free the programmer from focusing on details and focus on the big picture and uses parallel slackness: add small tasks for each process until all finishes

Question 15

what are the model components of BSP?

Answer 15

1. processing units and memory
2. router: for messaging between components
3. synchronization mechanisms acting every L units of time

Question 16

What are the computation steps for the BSP model?

Answer 16

1. at the beginning of a superstep each component is assigned a task
2. at the end of the time allotted to the superstep, a global check determines if the superstep is completed, goes to the next superstep, and if not, allocates another $L$ units of time to the super-step to allow it to continue execution

Question 17

not a question study petri-net and timing in this chapter

Answer 17

…

Question 18

Define what a communication protocol is.

Answer 18

a set of messages exchanged to help coordinate actions

Question 19

what is the implementation of communication protocol?

Answer 19

• error control mechanisms: using error detection and error correction
• flow control: provides feedback from the receiver, forces the sender to send an amount of data that the receiver can handle
• congestion control: ensure that the offered load of the network doesn’t exceed network capacity

Question 20

Define Logical clock

Answer 20

an abstraction necessary to ensure the clock condition in the absence of the global clock

Question 21

Write the rules to update the logical clock:

Answer 21

• Rule 1: LC(e) = LC + 1 if e is a local event
• Rule 2: LC(e) = max (LC, (TS(m)+1)) if e is a receive event