CMSC 321:
CMSC 321:
Operating Systems
Lecture 3
Processes
Processes
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Operating System Services - Lecture Slides | CMSC 321, Study notes of Operating Systems
Material Type: Notes; Professor: Barnett; Class: OPERATING SYSTEMS; Subject: Computer Science; University: University of Richmond; Term: Spring 2009;
Typology: Study notes
Pre 2010
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CMSC 321:CMSC 321:
Operating Systems
Lecture 3ProcessesProcesses
Operating System ServicesOperating System Services • What services must an OS provide?
at se
ces
ust a
OS p o
de
- program development– program execution– access to I/O– controlled access to files– system access (shared)
system access (shared)
- error detection & response– accounting (stats)
Hardware support for OS Features
pp
The Interrupt Mechanism •^
Interrupts occur due to hardware events
-^
Interrupts occur due to hardware events (completion of disk I/O, etc.) or softwareevents (expiration of a timer, reception of amessage, etc.).
- Instruction cycle is modifed to include a check
for pending interrupts after each instructionfor pending interrupts after each instructionexecution.
Hardware support for OS Features
pp
The Interrupt Mechanism •^
Interrupt vector
an area of system memory
•^
Interrupt vector
an area of system memory
containing a pointer to the interrupt handlerfor each type of interrupt.
- Interrupt handler first preserves processor
state for the suspended process, thenperforms actions necessary to service theperforms actions necessary to service theinterrupt.
- Different type of interrupts may have different
priorities: interupt handlers may themselvesbe interruptable!
Hardware support for OS Features
pp
Peripheral Handling: Direct Memory Access •^
All the work to complete the transfer occurs
-^
All the work to complete the transfer occurs between the device and the memorycontroller.
- Cycle stealing - since the memory controller
can handle only one request at a time
some
can handle only one request at a time, somememory requests from the CPU may bedelayed by requests from the deviceperforming DMA.
Hardware support for OS Features
pp
- Dual mode operation
- Monitor mode for execution of OS (also called
Monitor mode for execution of OS (also calledSupervisor mode or Kernel mode)
- User mode for execution of user programs
- Time slicing - prevents a "runaway" process
from dominating CPU usage. Hardware timerfrom dominating CPU usage. Hardware timerneeded to implement this feature.
ProcessProcess
•^
Most fundamental concept in OS
-^
Most fundamental concept in OS
- Process: a program in execution
- one or more threads (units of work)– associated system resources
- Program vs. process
- program: a passive entity– process: an active entity
- Program vs. process
- one or more threads (units of work)– associated system resources
process: an active entity
- For a
program
to execute, a
process
is created
for that programfor that program
Process ManagementProcess Management
•^
Fundamental task of any OS
-^
Fundamental task of any OS
- For processes, OS must:
- allocate resources– facilitate
multiprogramming
- allow sharing and exchange of info
g^
g
- protect resources from other processes– enable synchronization
- How?
- data structure for each process (coming soon…)– describes state and resource ownership– describes state and resource ownership
- How?
The Two-State Model
Two States: Not EnoughTwo States: Not Enough
- Running process makes I/O syscall
Running process makes I/O syscall– moved to “not running” state– can’t be selected until I/O is complete!
- “not running” should be two states: -^
blocked
: waiting for something, can’t be selected
d^
j^
t it hi
f^
CPU ti
-^
ready
: just itching for CPU time…
- Five states total -^
running
,^
blocked
,^
ready
-^
new
: OS might not yet admit (e.g., performance)
-^
exiting
: halted or aborted
- perhaps other programs want to examine tables & DS
Process State DiagramProcess State Diagram
Refined Queuing Diagram
P^
bl
bl
k d
diff
t^
t
Problem: processes blocked on different events
must search entire queue
Solution:
one queue for each type of event
Solution:
one queue for each type of event
Are Five States Enough?
g
Problem: Can’t have
all
processes in RAM
- Problem: Can’t have
all
processes in RAM
S
l^
ti
t^
di k
- Solution: swap some to disk
- i.e., move all or part of a process to disk
- Requires new state:
- i.e., move all or part of a process to disk
suspend
on disk
therefore not available to CPU
- on disk, therefore not available to CPU