2.1.5 Thinking Concurrently

Question 1

What is Concurrent Thinking

Answer 1

• Refers to systems where computatations can be executed simultaneously
• Quickly process massive data
• Concurrent systems are incredibly complex - huge increase in processing speeds.
• Recognising what parts of a problem can be solved at the same time.

Question 2

What is a Thread

Answer 2

• A thread is a small task running within a process
• A process can be made up of multiple threads
• Concurrency simultaneously running multiple threads within a single process rather than executing multiple processes at the same time

Question 3

What are the advantages of Concurrent Execution

Answer 3

• The advantages of concurrent execution are clear - can do 2 things at once.

Question 4

What are the disadvantages of concurrent execution?

Answer 4

• Deadlock
• Starvation
• Race Conditions

Question 5

What is deadlock?

Answer 5

• When every process is waiting for another to finish which is waiting for another to finish therefore no process is able to complete.
• Often cyclic, process A is waiting for process B which is waiting for C and is waiting for A.

Question 6

What are the 4 conditions that must combine simultaneously for there to be deadlock?

Answer 6

• Resources cant be shared - a printer can only be used by 1 process at a time
• A process can hold 1 resource while requesting another
• A resource can only be made available by the process currently holding it
• Circular waiting can occur

Question 7

What is starvation?

Answer 7

• When a process is denied the resources it needs.
• The process never gets enough CPU time to run

Question 8

What are Race Conditions?

Answer 8

• When 2 processes use the same memory location and the final result depends on the order in which the processes are run

Question 9

How do you identify which parts of a problem cam be executed at the same time?

Answer 9

• The 2 tasks must be completely independent of one another - any one process must not depend on the state of another if they are to be carried out simultaneously
• Secondly, conditions that will lead to deadlock, starvation and race conditions must be identified and avoided - easiest way to do this is to identify which area of the process can be solved separately without the need of resource
• Can use flowcharts