Threads SMP and Microkernels Chapter 4 1 2

Threads, SMP, and Microkernels Chapter 4 1

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Multithreading • Operating system supports multiple threads of execution within a single process • MS-DOS supports a single thread • UNIX supports multiple user processes but only supports one thread per process • Windows, Solaris, Linux, Mach, and OS/2 support multiple threads 3

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Process • Resource ownership - process includes a virtual address space to hold the process image and access to I/O • Scheduling/execution- follows an execution path that may be interleaved with other processes • These two characteristics are treated independently by the operating system 5

Process • Dispatching is referred to as a thread or lightweight process • Resource of ownership is referred to as a process or task 6

Thread • • An execution state (running, ready, etc. ) Saved thread context when not running Has an execution stack Some per-thread static storage for local variables • Access to the memory and resources of its process – all threads of a process share this 7

User-Level Threads 8

User-Level Threads • All thread management is done by the application • The kernel is not aware of the existence of threads • I/O requests causes the whole process to be blocked. 9

Kernel-Level Threads 10

Kernel-Level Threads • Windows is an example of this approach • Kernel maintains context information for the process and the threads • Scheduling is done on a thread basis • I/O requests only cause the affect thread to be blocked. 11

VAX Running UNIX-Like Operating System 12

Combined Approaches 13

Combined Approaches • Example is Solaris • Thread creation done in the user space and kernel space • Bulk of scheduling and synchronization of threads within application in both kernel and user space • Communication between threads can be done in kernel or user space. 14

Benefits of Threads • Takes less time to create a new thread than a process • Less time to terminate a thread than a process • Less time to switch between two threads within the same process • Since threads within the same process share memory and files, they can communicate with each other without invoking the kernel 15

Uses of Threads in a Single. User Multiprocessing System • Foreground to background work – Managing different processes with different levels of priority. • Asynchronous processing – Threads that can execute without care of what the other threads are doing. • Speed of execution – Faster to swap out threads than processes. 16

Threads - Review • Suspending a process involves suspending all threads of the process since all threads share the same address space • Termination of a process, terminates all threads within the process 17

Thread States • States associated with a change in thread state – Spawn • Spawn another thread – Block/Unblock – Ready/Running – Finish • Deallocate register context and stacks 18

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Processor Architectures 20

Categories of Computer Systems • Single Instruction Single Data (SISD) stream – Single processor executes a single instruction stream to operate on data stored in a single memory • Single Instruction Multiple Data (SIMD) stream – Each instruction is executed on a different set of data by the different processors 21

Categories of Computer Systems • Multiple Instruction Single Data (MISD) stream – A sequence of data is transmitted to a set of processors, each of which executes a different instruction sequence. Never implemented • Multiple Instruction Multiple Data (MIMD) – A set of processors simultaneously execute different instruction sequences on different data sets 22

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Symmetric Multiprocessing (MIMD) • Kernel can execute on any processor • Typically each processor does selfscheduling form the pool of available process or threads 24

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Symmetric Multiprocessing (MIMD) • What new issues might we have to deal with? – Having to worry about proper sharing of Memory – Two processes executing the same code either on purpose or by accident – The Kernel can be running on multiple processors at the same time. 26

Multiprocessor Operating System Design Considerations • Simultaneous concurrent processes or threads • Scheduling • Synchronization • Memory management • Reliability and fault tolerance 27

Microkernels 28

Microkernels • Small operating system core • Contains only essential core operating systems functions • Many services traditionally included in the operating system are now external subsystems – – – Device drivers File systems Virtual memory manager Windowing system Security services 29

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Benefits of a Microkernel Organization • Uniform interface on request made by a process – Don’t distinguish between kernel-level and userlevel services (Where all the services? ) – All services are provided by means of message passing • Extensibility – Allows the addition of new services • Flexibility – New features added – Existing features can be subtracted 31

Benefits of a Microkernel Organization • Portability – Changes needed to port the system to a new processor is changed in the microkernel not in the other services • Reliability – Modular design – Small microkernel can be rigorously tested 32

Benefits of Microkernel Organization • Distributed system support – Message are sent without knowing what the target machine is • Object-oriented operating system – Components are objects with clearly defined interfaces that can be interconnected to form software 33

Microkernel Design • Low-level memory management – Mapping each virtual page to a physical page frame (Kernel) – Memory protection and allocation (User-Level) 34

Microkernel • Supporting External Paging and Virtual Memory Management: – Grant : A User-Level process can grant/assign memory to another process. – Map : Placing one or more pages of memory in overlapping space. – Flush : The granter process can reclaim any memory. 35

Microkernel Design • Interprocess communication – Uses messages that contains a header and a body. • I/O and interrupt management – Interrupts recognized by the kernel, but handed off to a user-level process. 36

Closer Look at Windows and Solaris 37

Windows Processes • Implemented as objects • An executable process may contain one or more threads • Both processes and thread objects have built-in synchronization capabilities • Threads and Processes run in kernel mode 38

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Solaris • User-level and Kernel-level Threads • Process includes the user’s address space, stack, and process control block – Accessible by the Kernel Threads • Lightweight processes (LWP) – Shadow of the Process that allows the User. Level threads to function without making direct calls to the Kernel threads. 40

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Windows 2000 Thread States 42

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End 44

Remote Procedure Call Using Single Thread 45

Remote Procedure Call Using Threads 46

Multithreading 47

Adobe Page. Maker 48

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Closer Look at Solaris 52

Solaris Lightweight Data Structure • • Identifier Priority Signal mask Saved values of user-level registers Kernel stack Resource usage and profiling data Pointer to the corresponding kernel thread Pointer to the process structure 53

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Linux Task Data Structure • • • State Scheduling information Identifiers Interprocess communication Links Times and timers File system Address space Processor-specific context 55

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Linux States of a Process • • • Running Interruptable Uninterruptable Stopped Zombie 57