2. 2 Processor(s)Main MemoryDevices Process, Thread & Resource Manager Memory Manager Device Manager File Manager

3.  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 3

4.  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 4

5.  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) 5

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

7. 7 OS Address Space OS Address Space Control Unit OS interface … Machine Executable Memory ALU CPU P i Address Space P i Address Space P i CPU P i Executable Memory P i Executable Memory P k Address Space P k Address Space … P k CPU P k Executable Memory P k Executable Memory P j Address Space P j Address Space P j CPU P j Executable Memory P j Executable Memory

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

9. 9 OS interface … … … P i CPU Thrd j in P i Thrd k in P i …

10.  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 10

11.  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 11

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

13.  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 13

14.  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 14

15. 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 15

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

17. 17 Bootstrap Loader Process Manager Interrupt Handler P1P1 P2P2 PnPn … Machine is Powered up Initialization Load the kernel Service an interrupt Hardware process progress Execute a thread Schedule

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

19. 19 CPU New Thread Descriptor Old Thread Descriptor

20. 20 Process Manager Interrupt Handler P1P1 P2P2 PnPn Executable Memory Initialization 1 2 3 4 5 7 Interrupt 8 9 6

21.  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. 21

22. 22 EPROCESS … void *UniqueProcessId; … NT Executive KPROCESS … uint32 KernelTime; uint32 UserTime; … Byte state; NT Kernel

23.  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 23

24.  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 24

25.  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. 25

26. 26 ETHREAD EPROCESS KPROCESS NT Kernel KTHREAD NT Executive

27. 27 pid = fork(); UNIX kernel … Process Table Process Descriptor

28. 28 CreateProcess(…); Win32 Subsystem ntCreateProcess(…); … ntCreateThread(…); NT Executive NT Kernel … Handle Table Process Descriptor

29. 29

30. 30 Ready Blocked Running Start Schedule Request Done Request Allocate

31. 31 Runnable Uninterruptible Sleep Running Start Schedule Request Done I/O Request Allocate zombie Wait by parent Sleeping Traced or Stopped Request I/O Complete Resume

32. 32 Initialized CreateThread Ready Activate Select Standby Running Terminated Waiting Transition Reinitialize Exit Preempt Dispatch Wait Wait Complete Dispatch

33. Resource : Anything that a process can request, then be blocked because that thing is not available. R = {R j | 0  j < m} = resource types C = {c j  0 | for 0  j < m s.t. R j  R} = units of R j 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 c j 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 c j is unbounded. 33

34. 34 There is a resource manager, Mgr(R j ) for every R j Mgr(R j ) Process p i can only request n i  c j units of reusable R j p i can request unbounded # of units of consumable R j Process p i can request units of R j if it is currently running request Mgr(R j ) can allocate units of R j to p i allocate

35. 35 Process Resource Manager Process Blocked Processes Resource Pool request() release() Policy

36. 36 Parent-child relationship may be significant: parent controls children’s execution Ready-Active Blocked-Active Running Start Schedule Request Done Request Allocate Ready-Suspended Blocked-Suspended Suspend Yield Allocate Suspend Activate

37. 37 Program Process Abstract Computing Environment File Manager Memory Manager Device Manager Protection Deadlock Synchronization Process Description Process Description CPU Other H/W Scheduler Resource Manager Resource Manager Resource Manager Resource Manager Resource Manager Resource Manager Memory Devices Process Mgr

38. 38 System Call Interface File Manager Memory Manager Device Manager Protection Deadlock Synchronization Process Description Process Description CPU Other H/W Scheduler Resource Manager Resource Manager Resource Manager Resource Manager Resource Manager Resource Manager Memory Devices Libraries Process Monolithic Kernel

39. 39 Processor(s)Main MemoryDevices Libraries Process Subsystem User Subsystem Hardware Abstraction Layer NT Kernel NT Executive I/O Subsystem T T T T T T TT T