1. Implementing Processes, Threads, and Resources

2. Basic OS Functions Processor(s) Main Memory Devices Process, Thread &
Resource Manager
Memory
Manager
Device
File

3. What is a Process Classic process (used up to late 80s/early 90s)
Program in execution on a von Neumann computer
New abstraction divides aspects of classic process into two parts
Modern process: the part that defines a customized computational framework in which a program executes
Thread: the part that keeps track of code executions within this framework
Classic process = modern process with 1 thread

4. Process Manager Process manager creates the process abstraction
It implements a software environment for processes to run
Algorithms that define the behavior of the operating system
Data structures to preserve the state of the execution

5. Process Manager – cont.
Define what “things” threads in the process can reference – the address space (most of the “things” are memory locations)
Manage the resources used by the processes/threads
Tools to create/destroy/manipulate processes & threads
Tools to time-multiplex the CPU – Scheduling (Chapter 7)
Tools to allow threads to synchronization the operation with one another (Chapters 8-9)
Mechanisms to handle deadlock (Chapter 10)
Mechanisms to handle protection (Chapter 14)

6. Abstract Computing Environment
Process Manager – cont.
Program
Process
Abstract Computing Environment
File
Manager
Memory
Device
Protection
Deadlock
Synchronization
Description
CPU
Other H/W
Scheduler
Resource
Devices
Process Mgr

7. Implementing the Process Abstraction
OS Address
Space
Control
Unit
OS interface …
Machine Executable Memory
ALU
CPU
Pi Address
Pi CPU
Pi Executable
Memory
Pk Address
Pk CPU
Pk Executable
Pj Address
Pj CPU
Pj Executable

8. External View of the Process Manager
Hardware
Application
Program
Device Mgr
Process Mgr
Memory Mgr
File Mgr
UNIX
Windows
CreateThread()
CreateProcess()
CloseHandle()
WaitForSingleObject()
fork()
exec()
wait()

9. Modern Processes and Threads
OS interface …
Pi CPU
Thrdj in Pi
Thrdk in Pi

10. Processes A process is a sequential program in execution
The object program to be executed
The data on which the program will execute
Resources required by the program
The threads in the process
A host process environment
The status of each thread’s execution
Thread-specific data, such as a stack, a PC, and set of register values

11. Process Address Space Process address space
The collection of addresses a thread can reference
Normally refer to an executable memory location
Can refer to OS services and resources

12. The Address Space Process Files Other objects Address Space Binding
Executable
Memory
Other objects
Files

13. Building the Address Space
Some parts are built into the environment
Files
System services
Some parts are imported at runtime
Mailboxes
Network connections
Memory addresses are created at compile (and run) time

14. Process Manager Responsibilities
Create process abstraction
Create thread abstraction
Process/thread synchronization
Create resource abstraction
Resource protection
Cooperation with device manager to implement I/O
Implementation of address space

15. Modern Process Composed of: Address space
Program to define behavior of process
Data used by process
Resources needed for thread execution
Process created with a minimal set of resources
Additional resources allocated as needed

16. The Hardware Process
Hardware process refers to the iterative activity of the control unit
Repeatedly fetching and executing instructions

17. Tracing the Hardware Process
Bootstrap
Loader
Process
Manager
Interrupt
Handler P1 P2 Pn …
Machine is
Powered up
Initialization
Load the kernel
Service an interrupt
Hardware process progress
Execute a thread
Schedule

18. The Abstract Machine Interface
User Mode
Instructions
Application Program
Abstract Machine Instructions
Trap
Instruction
Supervisor Mode
fork()
create()
open() OS

19. Context Switching
CPU
New Thread Descriptor
Old Thread
Descriptor

20. Context Switching – cont.
Process
Manager
Interrupt
Handler P1 P2 Pn
Executable Memory
Initialization 1 2 3 4 5 7 8 9 6

21. Process Descriptors OS creates/manages process abstraction
Descriptor is data structure for each process
Register values
Logical state
Type & location of resources it holds
List of resources it needs
List of threads
List of child processes
Security keys
etc.

22. Creating a Process in UNIX
pid = fork();
UNIX kernel
Process Table …
Process Descriptor

23. Linux Process Descriptor
Execution of the collection of tasks - Managed by the Linux kernel
Struct task_struct is created when a process is created and it is “tied” into the list of tasks

24. Linux Process Descriptor
*Process descriptor is stored in dynamic memory
*Processes are dynamic entities whose lifetimes range from a few milliseconds to months.
Thus, the kernel must be able to handle many processes at the same time, and process descriptors
are stored in dynamic memory rather than in the memory area permanently assigned to the kernel.

25. Linux Process Descriptor

26. Windows NT Process Descriptor
EPROCESS …
void *UniqueProcessId;
NT Executive
KPROCESS
uint32 KernelTime;
uint32 UserTime;
Byte state;
NT Kernel
NT Kernel handles object management, interrupt handling, thread scheduling
NT Executive handles all other aspect of a process

27. Windows NT Process Descriptor – cont.
Kernel process object including:
Pointer to the page directory
Kernel & user time
Process base priority
Process state
List of the Kernel thread descriptors that are using this process

28. Windows NT Process Descriptor – cont.
Parent identification
Exit status
Creation and termination times.
Memory status
Security information
executable image
Process priority class used by the thread scheduler.
A list of handles used by this process
A pointer to Win32-specific information

29. Thread Abstraction The major tasks in managing a thread include
Create/destroy a thread
Allocate thread-specific resources
Manage thread context switching
The thread descriptor is the data structure where the OS keeps all information to manage that thread
Current state, execution stats, reference to associated process, related threads, etc.

30. Windows NT Thread Descriptor
ETHREAD
EPROCESS
KPROCESS
NT Kernel
KTHREAD
NT Executive

31. Creating a Process in NT
CreateProcess(…);
Win32 Subsystem
ntCreateProcess(…); …
ntCreateThread(…);
NT Executive
Handle Table
NT Kernel …
Process Descriptor

32. Windows NT Handles

33. Simple State Diagram Request Done Running Schedule Start Allocate
Ready
Blocked
Running
Start
Schedule
Request
Done
Allocate

34. UNIX State Transition Diagram
Request
Wait by
parent
Done
Running
zombie
Schedule
Request
Sleeping
I/O Request
Start
Allocate
Runnable
I/O Complete
Resume
Traced or Stopped
Uninterruptible
Sleep

35. Windows NT Thread States
CreateThread
Terminated
Initialized
Reinitialize
Activate
Dispatch
Exit
Wait
Waiting
Ready
Running
Wait Complete
Wait Complete
Select
Preempt
Transition
Dispatch
Standby

36. Resources
Resource: Anything that a process can request, then be blocked because that thing is not available. Resource Descriptors - Internal resource name - Total Units - Available Units - List of available units - List of Blocked processes

37. Resources
R = {Rj | 0  j < m} = resource types C = {cj  0 | for 0  j < m s.t. RjR} = units of Rj available Reusable resource: After a unit of the resource has been allocated, it must ultimately be released back to the system. E.g., CPU, primary memory, disk space, … The maximum value for cj is the number of units of that resource Consumable resource: There is no need to release a resource after it has been acquired. E.g., a message, input data, … Notice that cj is unbounded.

38. Using the Model There is a resource manager, Mgr(Rj) for every Rj
pi can only request ni  cj units of reusable Rj
pi can request unbounded # of units of consumable Rj
Process pi can request units of Rj if it is currently running
Mgr(Rj) can allocate units of Rj to pi
request
Mgr(Rj)
Process
allocate

39. A Generic Resource Manager
Blocked Processes
Policy
Process
request()
Process
release()
Resource Pool

40. Process Hierarchies Initial Process System Other Process Processes
Some OS use this hierarchical relationship - while others simply ignore it.

41. Process Hierarchies
Parent-child relationship may be significant: parent controls children’s execution
Request
Done
Running
Yield
Suspend
Request
Schedule
Suspend
Start
Ready-Active
Activate
Ready-Suspended
Allocate
Allocate
Suspend
Blocked-Active
Blocked-Suspended
Activate

42. Process Manager Overview
Program
Process
Abstract Computing Environment
File
Manager
Memory
Device
Protection
Deadlock
Synchronization
Description
CPU
Other H/W
Scheduler
Resource
Devices
Process Mgr

43. UNIX Organization Process Libraries Process Process
System Call Interface
Deadlock
Process
Description
File
Manager
Protection
Synchronization
Device
Manager
Memory
Manager
Resource
Manager
Scheduler
Monolithic Kernel
Devices
Memory
CPU
Other H/W

44. Windows NT Organization
Process
Process T T
Process T T T T
Libraries T T T
Subsystem
Subsystem
Subsystem
User
I/O Subsystem
NT Executive
NT Kernel
Hardware Abstraction Layer
Processor(s)
Main Memory
Devices