slides04

Question 1

cooperating processes and reasons for using them

Answer 1

-can affect or be affected by another process
-reasons:P
1. information sharing
2. computation speedup
3. modularity

Question 2

two models of IPC

Answer 2

1. shared memory
2. memory passing

Question 3

shared memory

Answer 3

• in user mode
• physical or virtual memory that is accessible to both processes
• producer/consumer does the following to access shared memory:
  1. create shared memory (must be on same computer)
  2. map shared memory into their address spaces
  3. read/write to shared memory
• tradeoff: cost of setting up shared memory space vs quick read/write

Question 4

message passing

Answer 4

• suitable for small number of message transfers
• processes read/write to a message queue in kernel

Question 5

types of communication links (3)

Answer 5

1. direct vs indirect
2. synchronous vs asynchronous
3. automatic vs explicit buffering

Question 6

direct vs indirect communication links

Answer 6

DIRECT
- 2 processes must be able to address each other
- advantages: processes could have multiple communication links

INDIRECT
- through a mailbox or port
- messages are consumable -> once consumed, it is no longer available

Question 7

advantages/disadvantages of indirect communication links

Answer 7

advantages:
- sender/receiver identities can change and communication program does not need to be updated eg. zoom

disadvantages
- higher delay of sending messages
- number of messages that can be sent is lower

Question 8

mailboxes vs ports

Answer 8

• ports only have one consumer; we know exactly where our message is going
• mailboxes can have multiple consumers; more fault tolerance, load balance between consumers

Question 9

synchronization with message passing

Answer 9

• message passing can be blocking or non-blocking

BLOCKING (SYNCHRONOUS)
- blocking send: sender is blocked until message is received
- blocking receive: receiver is blocked until message is available

NON-BLOCKING (ASYNCHRONOUS)
- non-blocking send: sender sends msg and continues
- non-blocking receive: receiver receives either a valid msg or a null msg
- minimizes wait times

• if both sender/receiver are synchronous: RENDEZVOUS (they reach and leave a point in execution at the same time)

Question 10

buffering in communication links

Answer 10

1. zero capacity: no messages are queued in link. sender must wait for the receiver
2. bounded capacity: finite length of n messages. sender must wait if buffer is full
3. unbounded capacity: infinite length. sender never waits.