Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Windows – Object manager and process management Mohammad S. Hasan Staffordshire University, UK
Windows – Object manager and process management
Slide 1
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Lecture Outline Windows object management Threads and processes in Windows Thread priority and scheduling Thread synchronisation Inter-process communication Internal process and thread representation
Windows – Object manager and process management
Slide 2
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Windows structure overview User Application Subsystem DLL
Environment Subsystem
System Support
System Services
NTdll.DLL User Mode Kernel Mode Executive API / Executive Services I/O Manager
File System
Cache Manager
Process and Thread Manager
Security Reference Monitor
Plug & Play Manager
Power Manager
Configuration Manager
Virtual Memory Manager
Object Manager / Local Procedure Call Device Drivers
Win32 User and GDI (Graphics Engine)
Graphics Drivers Kernel
Hardware Abstraction Layer (HAL)
Windows – Object manager and process management
Slide 3
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
System resources and data The OS needs to keep track of all the different resources Files I/O devices Memory
The OS keeps track of all processes (running programs) To do this the OS needs to keep info about these resources and their use.
CPU usage
Windows – Object manager and process management
Slide 4
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
System resources and data (Cont.) In many OS the info is maintained in various data structures which the operating system code manipulates In Windows the code that manipulates the data is kept together with the data in objects i.e. it uses an object oriented approach to manage the system resources and info about them Windows – Object manager and process management
Slide 5
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
System resources and data (Cont.) ALL entities and services on the system are represented internally by objects e.g. files are represented by objects, user programs when they are running on the computer, hardware resources like printers, communication ports, etc.
Motivation behind this is to provide a very modular structure which it is easy to update, extend, etc.
Windows – Object manager and process management
Slide 6
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
System resources and data (Cont.) Abstraction i.e. hiding details of implementation of the object’s class changes to internal implementation of an object's class can occur without affecting the code implementation of other object classes provided the interface remains unchanged
It also makes it easier to add new features and facilities to the system in the form of new object classes
Windows – Object manager and process management
Slide 7
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Object Manager The function of the object manager is to provide services that manage all the objects in the system Various other components in the Windows Executive and the Environmental Subsystems can create, use, and destroy objects using Object Manager Object Manager / Local Procedure Call Device Drivers
Graphics Drivers Kernel
Hardware Abstraction Layer (HAL) Windows – Object manager and process management
Slide 8
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Object manager (Cont.) Object manager provides a uniform set of services to the other components of the Executive - thus it simplifies object access
Windows – Object manager and process management
Slide 9
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Object Handles and Handle Table When a process wants to use an object it calls the object manager to get a handle to that object handles are like pointers in C that allow you to access the methods and data of an object Processes must have an object handle for every resource/item that it uses e.g. files, I/O devices, etc.
Windows – Object manager and process management
Slide 10
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Object Handles and Handle Table (Cont.) Each process has an Object Handle Table that contains all the handles to the various objects that the process has opened
Process
Windows – Object manager and process management
Slide 11
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Object structure Object Header
Object Body
Object name Object directory Security descriptor Quotas Open handle count Open handle list Object type
An object in the system has List of processes with handles to object
object header object body
Type Object
Object specific data
Windows – Object manager and process management
Slide 12
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Object structure (Cont.) Object header contains information such as the object's name, the hierarchy to which it belongs, security information (we will discuss that in more detail later), quota information, number of handles opened on object, pointer to a list of processes that have handles opened on object, pointer to an object that contains information about the object's type
Windows – Object manager and process management
Slide 13
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Object structure (Cont.) Object body contains information that is specific to the object Type object contains information that is common to all objects of a particular type (class) includes the code for all the methods that belong to the object class
Windows – Object manager and process management
Slide 14
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Object services The object manager provides a set of services that are common to all objects: create - creates object and returns a handle to it open - returns an object handle to calling process close - destroys handle delete - deletes object duplicate handle query information held in object
Windows – Object manager and process management
Slide 15
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Processes and threads In Windows a process consists of program code, execution context (the address space of the process plus such things as the access token), resources allocated to the process i.e. handles, and one or more threads
Threads are the units of execution – they execute program code using the processes context and resources
Windows – Object manager and process management
Slide 16
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Processes and threads (Cont.) A thread has its own context i.e. register values including instruction pointer, execution stack, and scheduling priority etc.
Threads are scheduled onto the processor, not a process. this is different from Linux which for scheduling purposes treats threads as a separate process that happens to share address space with another thread
Windows – Object manager and process management
Slide 17
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Processes and threads (Cont.) Processes and threads are managed by 2 components in Windows: the process and thread manager the kernel
Windows – Object manager and process management
Slide 18
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
The Kernel The kernel is responsible for: Thread scheduling Interrupt and exception handling Low level processor synchronisation Recovery after power failure
Windows – Object manager and process management
Slide 19
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
The Kernel (Cont.) In normal OS, the kernel refers to all the operating systems components that run in kernel mode. In Windows, this applies to all the Windows Executive components (everything below the line in the diagram – slide 3).
However, Windows applies the name kernel to just one component – a low level layer of the OS that manages much of the execution of threads within processes
Windows – Object manager and process management
Slide 20
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
The Kernel (Cont.) The kernel uses objects to represent and manage low level threads and processes However these kernel objects are different from those managed by the Object Manager They are lower level and provide support for the higher level objects used by the Object Manager
Windows – Object manager and process management
Object Manager (High Level Object)
Kernel (Low Level Object)
Slide 21
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Process and thread manager Process manager is part of the Windows Executive. implements the representation of processes and threads that are available to other parts of the Executive and provides high level services to manage and control processes and threads
Windows – Object manager and process management
Slide 22
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Process and thread manager (Cont.) Process and thread manager provides functions to Create and destroy processes Control resource allocation to processes Keep track of information about processes and threads
Processes are created by other processes by making a CreateProcess system call
Windows – Object manager and process management
Slide 23
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Process and thread manager (Cont.) Unlike Unix/Linux, the parent and child process are independent of each other. remember fork in Unix/Linux creates the child as a copy of the parent and hence has a copy of the parents address space
In Windows child process has completely separate address space. Hence Windows does NOT keep track of process hierarchies
Windows – Object manager and process management
Slide 24
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Thread scheduling Windows maintains a list of threads that are in the system Threads may be in one of several different states Ready – thread can execute but waiting for a processor Running – running on a processor Standby - selected to run next on a processor Waiting – unable to execute until some event occurs (typically I/O) Terminated
Windows – Object manager and process management
Slide 25
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Thread scheduling (Cont.) All processes have at least one thread known as the base thread – created when the process is created The kernel implements the dispatcher code, which determines which thread to run next The dispatcher implements pre-emptive scheduling among threads
Windows – Object manager and process management
Slide 26
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Thread scheduling (Cont.) The dispatcher schedules threads without reference to the process they belong to. hence a process that has more threads will if everything else is equal have a greater share of the processor
The scheduling algorithm is based on a multilevel priority queue approach with each thread having a priority and hence belonging to a given queue
Windows – Object manager and process management
Slide 27
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Thread scheduling (Cont.) A ready thread is placed in the queue which represents its assigned priority There are 32 priority queue levels highest priority – 31 lowest priority - 0
Dispatcher starts with highest priority queue and schedules threads in order in queue in round robin fashion
Windows – Object manager and process management
Slide 28
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Thread scheduling (Cont.) Each thread is given a time quantum to execute it either blocks itself waiting on some I/O or synchronisation event Or the quantum expires
Once the current queue is empty, the dispatcher proceeds to the next lowest priority queue and so on until the queues are all empty or a higher level priority thread enters a ready state and dispatcher pre-empts lower priority running thread Windows – Object manager and process management
Slide 29
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Thread scheduling (Cont.) Real-time Priority threads Highest priority levels (16-31) Needing immediate responsiveness Static priorities
Dynamic Priority thread Lower priority levels (0-15)
A processes base thread is given a base priority the minimum priority thread in that process
Windows – Object manager and process management
Slide 30
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Thread scheduling (Cont.) Each process has: a base priority class (which defines a range of priority levels which the base priority can take on) and a base priority level which specifies the actual base priority a thread should have in the base priority class for a given process
Windows – Object manager and process management
Slide 31
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Thread scheduling (Cont.) Each thread then takes on priority values dynamically i.e. it changes over time e.g. if the thread is delayed waiting on an I/O event, when the I/O event occurs and the thread becomes ready again, its priority is increased temporarily. The size of the increase depends on the length of the wait – the longer the wait the greater the increase in priority
Windows – Object manager and process management
Slide 32
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Traps and exception handling Kernel implements a trap handler which deals with hardware interrupts and processor exceptions Divide by Zero Exception
Trap handler operation disables interrupts, determines the cause of the interrupt, saves processor state, re-enables interrupts and dispatches interrupt service routine to handle it
Windows – Object manager and process management
Slide 33
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Thread synchronisation Windows provides a set of dispatcher objects which can be used for synchronisation of thread behaviour These dispatcher objects can be In a signalled state (when the event that the thread is waiting for occurs) or In a unsignaled state (when the event has not yet occurred)
Windows – Object manager and process management
Slide 34
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Thread synchronisation (Cont.) Event objects represent events such as I/O events – when the relevant event occurs the object manager sets the event object to the signalled state Mutex objects provide mutual exclusion – only one thread can have a mutex object – it does this by setting the object into an unsignaled state. Once the thread completes its activity it sets the mutex object to the signalled state Waitable timer objects – these objects remain unsignaled until a given time has elapsed
Windows – Object manager and process management
Slide 35
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Inter-process communication Threads (and hence also processes) can communicate using a variety of methods Pipes – work very similar to Unix – unidirectional communication via a shared buffer Sockets – similar to pipes but usually connect processes and threads on different machines Remote procedure calls – allows a thread in one process to invoke the execution of code in different processes address space File sharing is also implemented
Windows – Object manager and process management
Slide 36
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Internal process and thread representation Processes are represented within the NT Executive by a process control block (Executive Process Control or EPROCESS block). It stores information that other executive components use when manipulating a process process id, pointer to processes handle table, pointer to processes access token (used to determine security in access) etc.
Windows – Object manager and process management
Slide 37
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Internal process and thread representation (Cont.) Also contains a pointer to a kernel level process block (KPROCESS block). This contains information when used in scheduling a process, such as priority, time quantum to be used, etc. EPROCESS blocks are held in a linked list Thread information at the NT Executive level is held in an Executive Thread block (ETHREAD block)
Windows – Object manager and process management
Slide 38
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
Internal process and thread representation (Cont.) As with processes the ETHREAD block includes a pointer to a kernel level kernel thread block (KTHREAD block)
Windows – Object manager and process management
Slide 39
Mohammad S. Hasan
Faculty of Computing, Engineering & Technology
References Operating System Concepts. Chapter 22.
Windows – Object manager and process management
Slide 40
