Windows Threading

[CMSC 621] Advanced Operating Systems Windows Threading Colin Roby Jaewook Kim

Threads Interface Microkernel Multi-Processor Computing System   P P P P P P P Processor Process Thread OS, Process, and Thread for Windows OS Applications Programming paradigms Operating System Hardware

Legacy Window Threading Model (Co-operative Threading – Windows 3.1 and 95)

Co-operative Threading • Used by old 16-bit Window Platform • Invented to overcome the lacking of a hardware timer • Thread continues execution until • Thread terminates • Thread executes an instruction causing wait (e.g., IO) • Thread volunteers to stop (invoking yield or sleep) Terminate (call scheduler) Exited Running Scheduler dispatch Block for resource (call scheduler) Yield (call scheduler) Create Ready Blocked Resource becomes available (move to ready queue)

Architecture for Cooperative Threading Model • Use serialized message queue • All user input from keyboard & mouse are queued • Next message is not sent to program until current message is fully processed • Message based program interaction • Prior to receiving message, program stays dormant in memory • Message queue sends message to program • Program starts processing message • Program returns control back to window

Advantages & Disadvantages • Advantage • Safe and easy to use. • No need to worry about other threads changing shared variables due to its exclusive nature • Disadvantage • Only one thread can be active • Threads depend on each other to yield control, results in performance decrease in heavily loaded systems.

Threading Models from Windows NT to 2003(Preemptive Threading)

Preemptive Multiprocessing • Preemptive multi-processing operating system • The OS schedules the CPU time • The application can be preempted by OS scheduler Terminate (call scheduler) Exited Running Scheduler dispatch Block for resource (call scheduler) Yield, Interrupt (call scheduler) Create Ready Blocked Resource free, I/O completion interrupt (move to ready queue) * Kai Li – Non-Preemptive and Preemptive Threads

Windows Thread • The unit of execution (in UNIX, Process is the unit) • Basically one-to-one mapping • Fiber Library for the M:M Model • Each thread contains • A thread id • Register set • Separate user and kernel stacks • Private data storage area • The register set, stacks, and private storage area are known as the context of the threads • The primary data structures of a thread include: • ETHREAD (executive thread block) • KTHREAD (kernel thread block) • TEB (thread environment block)

Windows Thread Types • Single Threading • Each process is started with a single thread • Multiple Threading • A thread can be created by Win32 Pthread or Windows Thread API • Hyper Threading • Simultaneous multithreading technology on the Pentium 4 microarchitecture by Intel • Supported by Windows 2000 or more

Windows Threading Models • Win32 Threading Model • Win32 Pthread or Windows Thread API • COM (Component Object Model) Threading Model • Single Threaded Apartments (STA) • Multi Threaded Apartments (MTA) • Both Threading Model (STA or MTA)

Some of Win32 calls for managing processes, threads and fibers Win32 Threading API Calls

Win32 Threading Example start_servers( ) { HANDLE thread; DWORD id; thread = CreateThread(0, // security attributes 0, // default # of stack pages allocated (LPTHREAD_START_ROUTINE) server, // start routine (LPVOID)0, // argument 0, // creation flags &id); // thread ID WaitForSingleObject(thread, INFINITE); ... } DWORD WINAPI server(void *arg) { while(TRUE) // get and handle request return(0); }

Win32 Threading Example cont. rlogind(int r_in, int r_out, int l_in, int l_out) { HANDLE in_thread, out_thread; two_ints_t in={r_in, l_out}, out={l_in, r_out}; in_thread = CreateThread(0, 0, incoming, &in, 0, &id); out_thread = CreateThread(0, 0, outgoing, &out, 0, &id); WaitForSingleObject(in_thread, INFINITE); CloseHandle(in_thread); WaitForSingleObject(out_thread, INFINITE); CloseHandle(out_thread); }

Win32 Threading Example cont. ExitThread((DWORD) value); return((DWORD) value); WaitForSingleObject(thread, timeOutValue); GetExitCodeThread(thread, &value); CloseHandle(thread);

COM Threading • Components don’t live on threads • An instance is a ‘chunk’ of memory associated with an apartment • Apartments determine which threads can call the component • Thread switch is decided by the proxy based on apartment and threading model

COM Threading (STA vs. MTA) COM Object COM Object

COM Threading Example int main() { /* ::CoInitializeEx(NULL, COINIT_APARTMENTTHREADED); for STA */ ::CoInitializeEx(NULL, COINIT_MULTITHREADED); /* for MTA */ DisplayCurrentThreadId(); ILegacyCOMObject1Ptr spILegacyCOMObject1; spILegacyCOMObject1.CreateInstance(__uuidof(LegacyCOMObject1)); spILegacyCOMObject1 -> TestMethod1(); ::CoUninitialize(); return 0; }

Threading Model for Multicore System

Thread Management • Program actively assigns software thread to hardware thread. • Assign thread – strongly suggests which hardware thread should the software thread run on • Program passively relies on window scheduler to assign software thread to hardware thread • Efficiency of the threading is dependent upon the scheduling algorithm.

Hardware Design Variance • Two hardware thread share one core • This is known as simultaneous multi-threading (aka Hyper-Threading) • Multiple cores within the same cpu, one or more hardware thread on each core • Existing architecture includes dual-core, quad core.

Detecting multicore cpu and hardware thread • Window relied on threading packages provided by processor manufactures to detect the number of cpu cores and available hardware • Detect the cpu core topology – how many real hardware threads exist • Detect the relationship between the hardware threads such as sharing data caches or sharing instructions set

Mechanics of Window Scheduler • Preemptive, time slicing based • Using system clock to interrupt each thread • Each thread is allocated a fixed amount of time - quantum • Priority Driven • Highest priority ready thread always run first • Higher priority thread will interrupt lower priority thread before its time slicing is used up, or even before it starts its quantum • Manages processor affinity • Assign a thread to a particular processor

Processor Preference for Window Scheduler • Each thread maintains two CPU numbers stored in the kernel thread block: • Ideal processor – the preferred processor the thread should run on (often specified by programmer) • Last processor – the processor on which the thread last ran • Scheduler processor assignment preference: • If the ideal processor is idle, pick the ideal processor • Pick the last processor if it is idle • Pick the executing processor – where the current scheduling code is running • Scan all the cpu from highest cpu number to lowest cpu number.

Additional Slides

Processes and Threads (1) Basic concepts used for CPU and resource management

Processes and Threads (2) Relationship between jobs, processes, threads, and fibers

Windows Threading Architecture

One-to-one Threading Model • A process in Windows XP is inert; it executes nothing • A process simply owns a 4GB address space that contains code and data for an application. • In addition, a process owns other resources, such as files, memory allocations, and threads. • Every process in Windows XP has a primary thread. • Threads in Windows XP are kernel-level threads. • Per-thread data structures: • Total user/kernel time, kernel stack, thread-scheduling info., • Thread-local storage array, thread environment block (TEB), • List of objects thread is waiting on, synchronization info. Etc.

Fibers vs. Threads • Fibers vs. Threads • Fibers are often called “lightweight” threads. • They allow an application to schedule its own “threads” of execution. • Fibers are invisible to the kernel. • They are implemented in user-mode in Kernel32.dll • Fibers interface • ConvertThreadToFiber() converts a thread to a running fiber. • A new fiber can be created using CreateFiber(). • The new fiber runs until it exits or until it calls SwitchToFiber(). • Fibers provide a functionality of the many-to-many model.

Thread Cancellation • Terminating a thread before it has finished • Two general approaches: • Asynchronous cancellation terminates the target thread immediately • Deferred cancellation allows the target thread to periodically check if it should be cancelled

References1. Detecting Multi-Core Processor Topology in an IA-32 Platform by Khang Nguyen and shiHjon Kuo (Intel software network)2. Inside Microsoft Windows 2000 by David A Solomon and Mark E. Russinovich3. Programming Windows 95 by Charles Petzold - Microsoft Press.

Windows Threading