Chapter 3 - Processes

Question 1

Cascading termination

Answer 1

If a process terminates in any fashion, then all children are also terminated. Seen in Windows.

Question 2

Zombie

Answer 2

Process that has terminated, but whose parent has not yet called the WAIT() function. Every process is a zombie at some point, but generally only for a brief moment.

Question 3

Orphan

Answer 3

Parent process does not call WAIT() and instead terminates, leaving its child process alone.

Question 4

Shared memory

Answer 4

Page 122. Model of interprocess communication. A region of memory that is shared by cooperating processes. Processes can read/write data to the shared region. Can be faster than message passing.

Question 5

Message passing

Answer 5

Page 122. Model of interprocess communication. Communication occurs by means of messages exchanged between cooperating processes. Useful for exchanging smaller amounts of data because no conflicts need to be avoided. Easier to implement in a distributed system. Used for Netflix, etc.

Question 6

Non-blocking

Answer 6

Page 126. Send a message and move along – do not wait for RECEIVE(). Part of message passing.

Question 7

Blocking

Answer 7

Page 126. Send a message and enter the [Waiting] state until RECEIVE() occurs. Part of message passing.

Question 8

[Flowchart] Message passing mechanisms

Answer 8

Message passing mechanisms > Direct > Symmetric
MPM > Direct > Asymmetric
MPM > Indirect > OS owns mailbox
MPM > Indirect > Process owns mailbox

Question 9

Direct interprocess communication (Symmetric)

Answer 9

SEND(PID1, message) . . . RECEIVE(PID2, message)

Need to know each other’s PID before communication.

Question 10

Direct interprocess communication (Asymmetric)

Answer 10

SEND(PID1, message) . . . RECEIVE(&PID2, message)
OS supplies the sender’s PID in place of &PID2.
Need to know each other’s PID before communication.

Question 11

Indirect interprocess communication (OS owns)

Answer 11

SEND(mailbox1, message) . . . RECEIVE(mailbox1, message)
SSC may create the mailbox, but the OS can own it – OS-owned mailboxes afford greater flexibility. Many processes can read/write to this mailbox. If the process is terminated, the mailbox may persist.

Question 12

Indirect interprocess communication (Process owns)

Answer 12

SEND(mailbox1, message) . . . RECEIVE(mailbox1, message)

If the process owns it, only the process can read from the mailbox unless it allows other processes to read from it.

Question 13

Mailbox

Answer 13

Also called port. An object into which messages can be placed by processes and from which messages can be removed (‘received’). Each mailbox has a unique ID. Used with indirect communication.

Question 14

Blocking send

Answer 14

“If I can’t do what I want, I’m gonna go to sleep.”

The sending process is blocked until the message is received by the receiving process or by the mailbox.

Question 15

Nonblocking send

Answer 15

The sending process sends the message and resumes operation without waiting for message receipt.

Question 16

Blocking receive

Answer 16

The receiver blocks until a message is available.

Question 17

Nonblocking receive

Answer 17

The receiver retrieves either a valid method or a null.

Question 18

Rendevous

Answer 18

Occurs between the sender and receiver when both SEND() and RECEIVE() are blocking.
Zero capacity mailbox.
Helps each process know roughly where the other process was.

Question 19

Channel capacity + three types of capacity

Answer 19

How many unread messages may sit in a mailbox.
“Unbounded capacity” = SEND() can never block, because the mailbox can never be full. “System with automatic buffering.”
“Bounded capacity” = SEND() must block until space is available. “System with automatic buffering.”
“Zero capacity” = mailbox cannot have any messages waiting in it. SEND() must block until the recipient receives the message. “Message system with no buffering.”

Question 20

Socket

Answer 20

Page 136.
Endpoint for communication.
Two processes communicating over a network use two sockets – one for each process. Identifiable by an IP address concatenated with a port number (146.86.5.20:1625).
Generally use client-server architecture.

Question 21

Connection-oriented (TCP) sockets

Answer 21

Page 137.

Question 22

Connectionless (UDP) sockets

Answer 22

Page 137.

Question 23

Loopback

Answer 23

Page 138.

Question 24

Port

Answer 24

Page 139.

Question 25

Pipe

Answer 25

Page 142.

Question 26

CHAPTER SUMMARY

Answer 26

Page 147.

Memorize this as much as possible.

Question 27

Hardware context

Answer 27

Includes general purpose registry, etc.