System Components and Kernel Responsibilities

1. System Components • There are three main protected modules of the System • The Hardware Abstraction Layer • A virtual machine to configure all devices and hardware to use one kernel and one set of device drivers • The Kernel • The Executive • Five User Mode Subsystems

2. Kernel • Operates by using a set of kernel objects whose attributes store kernel data and whose methods perform kernel activities • Kernel Dispatcher – the object type of all kernel calls • remain in memory • never pre-empted • Software Interrupts

3. First and Second Kernel Responsibilities • Thread Scheduling • 2 classes, variable and real time • variable – contains threads with priorities from 0 to 15 • real time – contains threads with priorities from 16 to 31 • Interrupt and Exception Handling • Trap Handlers deal with simple exceptions • The exception dispatcher creates an exception record containing the reason for the exception and finds an exception handler to deal with it

4. Third and Fourth Kernel Responsibilities • Low-level processor synchronization • Recovery after Power Failure

5. Executive • Object Manager • Virtual Memory Manager • Process Manager • Local Procedure Call Manager • I/O manager • Cache manager • Security Reference Monitor • Plug and Play and Power Managers • Registry • Booting

6. User Mode Subsystems • OS/2 • Win 16 • Win 32 • MS-DOS • POSIX • Protected Subsystems

7. Programmer Interface • Access to Kernel Objects • Done by CreateXXX() (where XXX is an object name) and terminated by the CloseHandle() function • Sharing Objects Between Processes • Process Management • Interprocess Communication • Memory Management

8. Sharing Objects Between Processes • Can be done by one of three methods • Inherited • Passing the Kernel Object a second name (may cause overlapping object names) • DuplicateHandle() function – uses some other method of interprocess message passing to share Kernel Object handles

9. Process Management • Instance Handles – virtual address where every dynamic link library or executable file loaded into a process • Scheduling Rule – distinguishes between the foreground program and all background programs tripling the foreground program's time quant • Thread Priorities – determined by it's class (idle, normal, high, realtime) and can be adjusted more so by use of the SetThreadPriority() function • Thread Synchronization – if multiple threads attempt to enter the critical section of some specified code only one section will be permitted to proceed

10. Process Management (Continued) • Fibers • User-mode code that is scheduled according to user-defined scheduling algorithms • Only one fiber may execute concurrently, even in a multiprocessor environment • Thread Pool – provides user-mode programs with three services in an attempt to increase performance • A Thread Queue • API that can bind callbacks and waitable handles • APIs to bind callbacks and timeouts

11. Interprocess Communication • Can be handled in several ways • Sharing Kernel Objects • Message passing – particularly popular for GUI applications • Posting a Message – Asynchronous • Sending a Message – Synchronous • Can send Data as well as a Message

12. Memory Management • Virtual Memory • Processes reserve or commit virtual memory • A process may lock some committed pages into physical memory so as to not be removed – maxes at 30 unless specifically changed • Memory Mapping Files • Used for multiple processes to use the same memory without duplicating it into multiple memory spaces

13. Memory Management Continued • Heaps • Reserved address space for Win32 API processes • Synchronized to prevent the heap's space-allocation data structures from being damaged by concurrent updates by multiple threads • Thread Local Storage – allocates global storage on a per-thread basis (creating a 'local' global storage for each thread)