Lecture 4: Processes

Question 1

define process

Answer 1

program in execution

Question 2

5 parts in process

Answer 2

• text section (program code)
• program counter (current activity)
• heap (memory dynamically allocated during run time)
• data section containing global variables
• stack containing temporary data

Question 3

5 states in process

Answer 3

1. new: program being created
2. running: instruction being executed
3. waiting: process waiting for event to occur
4. ready: process waiting to assign to processor
5. terminate: process finish execution

Question 3

what is process control block (PCB)

Answer 3

information associated with each process
- process state
- program counter
- CPU register
- CPU scheduling information
- memory management
- accounting information
- I/O status information

Question 3

define process schedulling

Answer 3

quickly switch process onto CPU for time-sharing to maximize CPU use

Question 4

3 scheduling queue

Answer 4

• job queue: set of all processes in system
• ready queue: set of processes in main memory, ready and waiting for execute
• device queue: set of processes waiting for I/O device

Question 5

representation of process scheduling

Answer 5

1. new process is put in ready queue, waiting for execution
2. the process will be allocated the CPU and executed
3. one of the events will occur
   - process issue I/O request and enter I/O queue to waiting
   - process create new child process and waiting for child to terminate
   - process is removed from CPU. causing an interrupt, put back to ready queue

Question 6

2 types of scheduler

Answer 6

long-term scheduler (job scheduler)
- select process to be bring into ready queue
- may be slow
- determine degree of multiprogramming

short-term scheduler (CPU scheduler)
- select process to be execute next and allocate CPU
- must be fast

Question 7

I/O-bound process and CPU-bound process

Answer 7

I/O-bound process
- spend more time on I/O than computation
- many short CPU burst

CPU-bound process
- spend more time on computation
- few long CPU burst

Question 8

define context switching

Answer 8

when CPU switches to another process, the system must saved the state of old process, and load the saved state for new process

Question 9

define process creation

Answer 9

Parent process create children process, than continue to create other children process, forming a tree of processes
- process is identified and managed via process identifier (pid)
- 3 possible result of resource sharing
- 2 possible result of execution
- 2 possible result of address space

Question 10

reasons for cooperating process

Answer 10

• sharing information
• convenient
• speedup computation
• modularity

Question 11

two models of Interprocess Communication (IPC)

Answer 11

• shared memory
• message passing

Question 12

two types of process

Answer 12

• independent (cannot affect or to be affected by other process execution)
• cooperating (can ‘’ )

Question 13

define message passing

Answer 13

mechanism for process to communicate and synchronize the actions
- message system allow process to communicate with each other without resorting shared variable

Question 14

2 steps in message passing

Answer 14

• create communication link
• exchange messages via send/receive

Question 15

4 advantages of threads

Answer 15

• scalability
• lower cost: shared resources make economical to create and context switch thread
• resource sharing: allow different thread of activity within the same address space
• responsiveness: program continue to run even part of it is blocked

Question 16

challenges in multicore programming

Answer 16

• identify task
• balance
• data splitting
• data dependency
• testing and debugging

Question 17

three primary user thread libraries

Answer 17

• POSIX thread
• Win32 thread
• Java thread

Question 18

define swapping

Answer 18

• process can be reintroduced into memory and continue its execution where it left off