Processes Flashcards
What does a multiprogramming system, from a high level context, do?
In the space of a second, the CPU is able to switch and work on multiple different things.
What word is used to describe the apparent appearance of parallelism? What does it describe?
Pseudo-parallelism.
It describes the appearance of actual parallelism whereby multiple processes are being handled by multiple CPUs
What is a process? What three things does it contain?
An executing program.
Contains registers, program counter and variables.
What’s the difference between a process and a program?
Cooking.
A recipe, a set of instructions, is a program.
The process are the activities which feed into (eyyy) the recipe.
Give an analogy for a process switch for baking
Cook's son comes into kitchen with bee sting. Cook bookmarks recipe page. Cook sorts out son. Cook gets back to recipe page. Cook continues cooking.
What four things cause a process to be created?
System initilsation
Execution of a process creation system call by a running process
A user request to create a new process
Initiation of a batch job
What are daemons?
Processes that ‘stay in the background’.
Give examples of daemon processes
Accepting incoming email.
Accepting incoming requests for a website.
What is system initilisation processes?
The first processes when starting a computer.
Give an example of when a process might be created by another process?
Large amount of data being collected through a network.
Setting up a process that takes the data and places it in a shared buffer.
Setting up another process and having that work upon the data.
How might you make a process created by another process run faster?
On a multiprocessor system, running a process that is independent of but related to (in a holistic sense) the first process on another CPU could make the program run faster.
Give an example of an interactive system process being created?
User typing a command or clicking an icon.
Give four examples of how processes terminate
Normal exit
Error exit
Fatal error
Killed by another process
Which two process termination examples are voluntary
Normal exit
Error exit
Which two process termination examples are involuntary
Fatal error
Killed by another process
In most cases, what happens when a process finishes?
The compiler executes a system call to the operating system to say ‘hey, I’m done’.
Give an examle of an error exit
Attempting to compile a file that doesn’t exist. It’ll just erorr exit.
Give an example of a fatal error in terms of processes
Dividing by zero in the code.
Attempting to access memory that either doesn’t exist or is privildged.
UNIX can do something unique in terms of fatal errors. What?
Able to handle exceptions and create signals rather than fully terminate the process.
What happens when a kill process happens?
A process issues a system call for another process to be killed. It would need adequate permissions to do this.
What is the kill process called in Windows and UNIX?
Unix = kill Windows = TerminateProcess
Give two reasons why a process might block?
Process cannot logically continue (waiting for input).
It is conceptually ready, but CPU has decided to allocate time to another process.
What are the three states a process can be in?
Running
Blocked
Ready
Describe ‘running’ in terms of processes
The process is actually being seen to by the CPU
Describe ‘blocked’ in terms of processes
The process is held up from getting access to the CPU It is in state where it will not be seen to. It needs to move from the blocked state before it will be handled by the CPU
Describe ‘ready’ in terms of processes
The process is in a state of readiness, able to be seen by the CPU but not yet being handled by it.
What table is used to implement processes?
Process table
What information is included in a process table entry
Process' state Program counter Stack pointer Memory allocation its files its scheduling informaion
essentially, everything that is needed to make the process run if the CPU moved it from blocked to ready to running, or ready to running
What can cause process switch?
Clock interrupt I/O interrupt Memory fault Trap Supervisor / system call
What happens in a process switch?
- Contents of process saved
- Process blocks updated
- Process moved into appropriate queue (blocked/ready)
- Run scheduler to select new process
- Update process block
- Run next process
