Chapter 3 (Process Description and Control) Flashcards
What are the two states of a process?
Running and not running
What does the OS do when a new process is created?
Builds the data structures needed and allocates space in main memory
What are the four primary reasons a process is created?
New batch job submitted
Interactive logon occurred
OS creates one for some service
Spawning an existing process
T/F The two state model is adequate
F
What is a problem with the two state model?
Requires the dispatcher to search the not-running queue, looking for a process that is not blocked
What states are in the five state model?
Running Ready Blocked New Exit
Null -> new
Process creation
New -> Ready
OS is ready for a new process
Ready -> Running
Based on scheduling algorithm
Running -> Exit
On termination
Running -> Blocked
Service call, I/O request
Blocked -> Ready
Waited event occurs
Ready -> Exit
Terminated due to parent
Blocked -> Exit
Terminated due to parent
What are the two suspend states?
Blocked/Suspend
Ready/Suspend
What is the blocked/suspend state?
Suspended and awaiting an event
What is the ready/suspend state?
Suspended and ready to run
Blocked -> Blocked/Suspend
To free memory
Blocked/Suspend -> Ready/Suspend
If event occurs while blocked/suspend
Ready/Suspend -> Ready
If no ready processes, or if suspended process is higher priority than ready queue processes
Ready -> Ready/Suspend
If need to free up memory and there are no blocked processes, or a ready process if of lower priority than the blocked processes
new -> Ready/Suspend and New -> Ready
Could add new process to either queue. Might add to the ready/suspend queue if no room in memory or if desired to let OS setup the new process before loading it
Blocked/Suspend -> Blocked
If suspended blocked process has higher priority than any suspended ready process
Running -> Ready/Suspend
Rather than returning to the ready queue, could be sent to the ready/suspend to free up memory for some higher priority process
Various -> Exit
If terminates due to normal completion or error, or by parent, or on some systems if parent terminates
T/F The suspend state may be used for other occasions besides swapping a process out of memory
T
What are the characteristics of a suspended process?
Not immediately available for execution
May or may not be waiting on an event
Process was suspended by an agent
Process stays suspended until the agent activates it
What are reasons for suspension?
Swapping
OS Reason
User request
Timing
Parent request
Why swap for suspension?
To free main memory
What is an OS reason for suspension?
OS thinks process is causing a problem (deadlock)
What user request would cause a suspension?
To debug
Why would timing suspend a process?
If infrequently run
Why would a parent request suspend a process?
To examine a child process or its activity
What are the 4 categories of information the OS maintains tables of?
Memory tables
I/O tables
File tables
Process tables
What does the memory table keep track of?
Allocation of main memory to processes
Allocation of secondary memory to processes
Protection attributes of blocks of main or virtual memory
Information needed to manage virtual memory
What do I/O tables keep track of?
Availability of a device
Device assignment to a process
Device status
Operation status
Memory being used for a data transfer
What do file tables keep track of?
Their location in secondary storage
Their status
Other file attributes
What do process tables keep track of?
Where the process is located
Attributes of the process
Where is the information the OS needs to control a process located?
Process Control Block (PCB)
All of these together are referred to as the process image
User program
User data
System stack
Process Control Block
What are the three main parts of the process control block?
Process identification
Processor state information
Process control information
Process identification has numeric ID’s for…
The process
The parent of the process
The user of the process
What does the processor state include?
User-visible registers
Control and status registers
Stack pointers
What things are in the scheduling and state information?
Process state
Priority
Scheduling-related information
Event
T/F Creating a new process is a relatively short operation
F, relatively lengthy
When may a process switch occur?
Anytime the OS gains control again from the current process
What may give the OS control again?
Interrupt
A trap
A supervisor call
What is a trap?
Current instruction creates an error
What is a supervisor call?
I/O request
What are the two kinds of switching?
Mode switch
Process switch
What is a mode switch?
Switch away from process, for example, to run an interrupt handler
What is a process switch?
Switch from one process to another process
What is done for a mode switch?
Save context
Set PC to interrupt handler
Switch from user mode to kernel mode
Run interrupt handler
What happens upon the return of a mode switch?
Switch from kernel mode back to user mode
Set PC to program
Restore context
What is done for a process switch?
Save context
Update PCB of current process to a non-running state
Move PCB process to appropriate queue for the state
Select another process to run
Update PCB of the selected process in the running staate
Update memory-management data structures
Restore state of newly selected process
Does a process switch or mode switch require more work?
Process switch
What is the nonprocess kernel approach?
Executes the kernel outside of any process
T/F The idea of a process only applies to user programs in a nonprocess kernel approach
T
Is a nonprocess kernel approach common on newer or older OS’?
Older
In a process-based OS, what two kinds of processes does the OS support?
User processes
System processes
T/F All processes in a process-based OS can then be managed according to priority with some OS functions being low priority and others being high
T
