IPC

Question 1

What is IPC?

Answer 1

Inter-process communication (IPC) is a set of methods for data interchange among potential multiple threads in one or more processes

Question 2

Other names for IPC

Answer 2

inter-thread communication, inter-application communication

Question 3

2 types of processes.

Answer 3

Independent process.
Co-operating process.

An independent process is not affected by the execution of other processes while a co-operating process can be affected by other executing processes.

Question 4

What ways can processes communicate with each other?

Answer 4

• Shared Memory

- Message passing

Question 5

1) Shared memory communication, how does this work?

Answer 5

By writing and reading shared variables

Question 6

1) How does one process know when the other process wrote new info?

Answer 6

In some cases it wouldn’t know. - This would be in a load balancing program that just looks at the current load of the other process in the storage

When it does know - use polling (puts undue burden on the cpu)

Or it gets a software interrupt

Or semaphores or conditions could be used

Question 7

1) When using Semaphores what happens?

Answer 7

Process q could block till p changes s and sends signal that unblocks q

But these solutions don’t allow q to block automatically if s cannot contain all data.
- Here you need to use semaphores as an external protocol to implement a buffer

Question 8

1) What is the most efficient way to implement shared memory applications? (what function - in the Linux and Solaris 2.x OS)

Answer 8

mmap() function

or shmget() - another way to let multiple processes attach a segment of physical memory to their virtual address spaces

Question 9

1) mmap() function

Answer 9

The mmap() function shall establish a mapping between a process’ address space and a file, shared memory object, or typed memory object.

Question 10

1) shmget() function

Answer 10

returns the identifier of the System V shared memory segment associated with the value of the argument key. It may be used either to obtain the identifier of a previously created shared memory segment (when shmflg is zero and key does not have the value IPC_PRIVATE), or to create a new set.

Question 11

Is conventional shared memory distributed or centralized? and why?

Answer 11

It is centralized, found on one machine. This is because (even though distributed shared memory over LANs has been worked on) even if we implemented distributed shared memory (without message passing it is not ideal)

Question 12

Is shared memory used with client-server interaction?

Answer 12

No, not the best abstraction for clients sending server requests (requires coding as data structures unless structures encapsulated in monitors)

message passing is more appropriate

Question 13

functions to create and handle interrupts

Answer 13

Interrupt(process id, interrupt number) - service call letting a process cause an interrupt in another

Handle(interrupt number, handler) - associates a handler with an interrupt

Question 14

When a software interrupt is initiated what is allowed to be communicated?

Answer 14

Software interrupts allow only one bit information to be communicated -
that an event associated with the interrupt number has occurred.

They are typically used by an operating system to inform a process about the following events:

• The user typed the ``attention key’’.
• An alarm scheduled by the process has expired.
• Some limit, such as file size or virtual time, has been exceeded.

Question 15

What are Interrupt traps, software interrupts, and exceptions?

Answer 15

With all of them an event is processed asynchronously by a handler procedure.

Interrupt and trap numbers defined by hardware which is also responsible for calling the procedure in kernel

Question 16

Interrupt handler vs trap handler

Answer 16

Interrupt handler called in response to a signal from another device

while a trap handler is called in response to an instruction executed within the cpu

Question 17

where are interrupt and exception handlers called?

Answer 17

the user space

Question 18

A software interrupt handler is called in response to what?

Answer 18

the invocation of a system call

what does this mean ??? grrrr

Question 19

What are software interrupt numbers defined by?

Answer 19

The operating system

Question 20

What are exceptions defined and processed by?

Answer 20

The programming language

Question 21

Does the raiser of an exception identify which process should handle it?

Answer 21

No. meaning that exceptions are not IPC (inter-process communication) mechanisms

Question 22

What are Software interrupts when referred to in a PC environment?

Answer 22

traps to kernel-provided I/O routines

Question 23

What is the special instruction on the PC called INT for?

Answer 23

it invokes traps in PC environment or ‘Software interrupts’

Ex. int 16H (executes BIOS interrupt routine for processing the current character received from keyboard)

Question 24

What is the term Software interrupts similar to in Linux/ Unix?

Answer 24

signals

Question 25

Are signals (as seen in Linux/ Unix) or software interrupts the same thing as semaphores?

Answer 25

No, they are different.

But you do use the ‘signal’ operation on both