2. Chapter 6
Implementing
Processes, Threads,
and Resources

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

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

5. Process Manager Responsibilities
Define & implement the essential characteristics of a process and thread
Algorithms to define the behavior
Data structures to preserve the state of the execution
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 the (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. Modern Processes and Threads
Thrdj in Pi
Thrdk in Pi …
Pi CPU … …
OS interface …

7. Processes &Threads State Stack State Stack Map Address Space Map
Program
Static data
Resources

8. Process Address Space
Process address space is the collection of addresses that a thread can reference.
Normally, it refers to an executable memory location.
However, due to the nature of a process, a process address space can also be associated with other machine abstract elements-such as, files, device registers and other objects.

9. Memory-Mapped-Resources
1. Most of the components in a computer system can be referenced by memory addresses. (One of the exception is the processor it self)
2. The address space provides a uniform mechanism by which a process can reference bytes in all memory-mapped resources.
3. Each resource manager is responsible for binding addresses with addressable elements of the resource.

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

11. 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

12. Tracing the Hardware Process
Machine is
Powered up
Bootstap
Process
Manager
Interrupt
Handler P1
P,2 Pn
Loader
Load the kernel
Initialization
Execute a thread …
Schedule
Hardware process progress
Service an interrupt

13. Responsibilities of Process Manager
1. Process Creation and Termination
2. Thread Creation and Termination
3. Process/Thread Synchronization
4. Resource Allocation
5. Resource Protection
6. Co-operate with Device Manager to Implement I/O
7. Co-operate with the Memory Manager to Implement Memory Space

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

15. Context Switching-Abstract Machine switching
Executable Memory
Initialization 1
Process
Manager 9 6 4 2 5 8 3 7
Interrupt
Interrupt
Handler P1 P2 Pn

16. OS Families-Example POSIX Standard Description Release
POSIX system interfaces and headers SunOS 4.1
POSIX POSIX update Solaris 2.0
POSIX.1b-1993 real-time extensions Solaris 2.4
POSIX.1c-1996 threads extensions Solaris 2.6
POSIX shell and utilities Solaris 2.5
POSIX.2a-1992 interactive shell and utilities Solaris 2.5

17. 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
Security keys
etc. (see Table 6.1 and the source code of your favorite OS)

18. Windows NT Process Descriptor
EPROCESS …
void *UniqueProcessId;
NT Executive
KPROCESS …
uint32 KernelTime;
uint32 UserTime;
Byte state;
NT Kernel

19. Windows NT Process Descriptor (2)
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

20. Windows NT Process Descriptor (3)
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

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

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

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

24. Windows NT Handles

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

26. 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

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

28. Resources
Resource: Anything that a process can request, then be blocked because that thing is not available.
R = {Rj | 0  j < m} = resource types
C = {cj  0 |  RjR (0  j < m)} = 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.

29. 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
request
Mgr(Rj) can allocate units of Rj to pi
allocate
Mgr(Rj)
Process

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

31. 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

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

33. 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

34. 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