International Journal of Scientific & Engineering Research Volume 3, Issue 4, April-2012 1 ISSN 2229-5518 Setting CPU Affinity in Windows Based SMP Systems Using Java Bala Dhandayuthapani Veerasamy, Dr. G.M. Nasira Abstract—Multithreaded program involves multiple threads of control within a single program on single or multiple environments. In multithreaded programming model, a single process can have multiple, concurrent execution paths on CPUs. Thread affinity benefit a thread to run on a specific subset of processors. Multithreaded programming is written in many programming languages with an improvement of setting an affinity to threads. Java supports to develop multithreaded programming, while it does not contain any method to set an affinity for threads on CPU. This paper articulates the method to setting CPU affinity for threads in windows based SMP systems using Java. Index Terms— Affinity mask, JNA, Multithread, Thread, Windows programming —————————— —————————— 1 INTRODUCTION OST concurrent applications [3] are organized around its execution immediately. Once terminated, a thread cannot be Mthe execution of tasks: abstract, discrete units of work. resumed. Thread priority determines how that thread should be Dividing the work of an application into tasks treated with respect to the others. Thread priorities are integers simplifies program organization, facilitates error recovery by that specify the relative priority of one thread to another. As an providing natural transaction boundaries, and promotes absolute value, a priority is meaningless; a higher-priority concurrency by providing a natural structure for parallelizing thread doesn’t run any faster than a lower-priority thread if it is work. The first step in organizing a program around task the only thread running. Instead, a thread’s priority is used to execution is identifying sensible task boundaries. Ideally, tasks decide when to switch from one running thread to the next. are independent activities: work that doesn't depend on the This is called a context switch. Problems can arise from the state, result, or side effects of other tasks. Independence differences in the way that operating systems context-switch facilitates concurrency, as independent tasks can be executed thread of equal priority. Because multithreading introduces an in parallel if there are adequate processing resources. For asynchronous behavior to your programs, there must be a way greater flexibility in scheduling and load balancing tasks, each for you to enforce synchronicity when you need it. The monitor task should also represent a small fraction of your is a control mechanism first defined by C.A.R. Hoare. You can application's processing capacity. think of a monitor as a very small box that can hold only one A multithreaded program [5] contains two or more parts that thread. Once a thread enters a monitor, all other threads must can run concurrently. Each part of such a program is called a wait until that thread exits the monitor. thread, and each thread defines a separate path of execution. Windows supports concurrency among processes because Each thread in a multithreaded process [9] can be dispatched to threads in different processes may execute concurrently. a different processor in a multiprocessor system. This Moreover, multiple threads within the same process may be collaboration across multiple processors improves single- allocated to separate processors and execute simultaneously. application performance. Multithreading enables [5] you to A multithreaded process achieves concurrency without the write very efficient programs that make maximum use of the overhead of using multiple processes. Threads within the CPU, because idle time can be kept to a minimum. Threads exist same process can exchange information through their in several states. A thread can be running. It can be ready to run common address space and have access to the shared as soon as it gets CPU time. A running thread can be resources of the process. Threads in different processes can suspended, which temporarily suspends its activity. A exchange information through shared memory that has been suspended thread can then be resumed, allowing it to pick up set up between the two processes. Multiprocessor where it left off. A thread can be blocked when waiting for a programming is challenging because modern computer resource. At any time, a thread can be terminated, which halts systems are inherently asynchronous: activities can be halted or delayed without warning by interrupts, preemption, cache ———————————————— misses, failures, and other events. These delays are inherently Bala Dhandayuthapani Veerasamy is currently a Research Scholar in unpredictable, and can vary enormously in scale: a cache miss Information Technology, Manonmaniam Sundaranar University, India. E- might delay a processor for fewer than ten instructions, a page mail: [email protected] Dr. G.M. Nasira is currently working as an Assistant Professor-Computer fault for a few million instructions, and operating system Applications, Department of Computer Science, Govt Arts College preemption for hundreds of millions of instructions. (Autonomous), Salem -636007, Tamilnadu, India. E-mail: The general-purpose process and thread facility must [email protected] support the particular process and thread structures of the IJSER © 2012 http://www.ijser.org International Journal of Scientific & Engineering Research Volume 3, Issue 4, April-2012 2 ISSN 2229-5518 various OS clients. It is the responsibility of each OS "kernel32" Alias "SetThreadAffinityMask" (ByVal subsystem to exploit the Windows process and thread features hThread As Long, ByVal dwThreadAffinityMask As to emulate the process and thread facilities of its Long) As Long corresponding OS. An application client process issues its process creation request to the OS subsystem; then a process 1.2 Symmetric Multiprocessing Support in the subsystem in turn issues a process request to the Symmetric Multiprocessing (SMP) is a multiprocessing Windows executive. Windows enables the subsystem to architecture in which multiple CPUs, residing in one cabinet, specify the parent of the new process. The new process then share the same memory. It is the tightly coupled process of inherits the parent’s access token, quota limits, base priority, program tasks being shared and executed, in true parallel mode, and default processor affinity. by multiple processors who all work on a program at the same time. Typically, these have large, single units with multiple 1.1 Win32 API and Dynamic-Link Libraries processors that utilize shared memory, I/O resources, and, of Windows programming [12] is useful to start off with some course, a single operating system. The term SMP is so closely appreciation of some new terms intrinsic to Windows: objects, associated with shared memory that it is sometimes handles, instances, messages, and callback functions. These misinterpreted as standing for “shared memory parallel”. SMP give us the mechanics of programming in this environment, systems range from two to as many as 32 or more processors. that is, they are tools that we need to use. A Dynamic Link However, if one CPU fails, the entire SMP system is down. Library (DLL) is a module that contains functions and data Clusters of two or more SMP systems can used to provide high that can be used by another module (application or DLL). availability (fault resilience). If one SMP system fails, the others DLLs provide a way to modularize applications so that their continue to operate. functionality can be updated and reused more easily. DLLs Windows supports an SMP hardware configuration. The also help reduce memory overhead when several applications threads of any process, including those of the executive, can use the same functionality at the same time, because although run on any processor. In the absence of affinity restrictions, the each application receives its own copy of the DLL data, the microkernel assigns a ready thread to the next available applications share the DLL code. The Windows application processor. This assures that no processor is idle or is executing programming interface (API) is implemented as a set of DLLs, a lower-priority thread when a higher-priority thread is ready. so any process that uses the Windows API uses dynamic Multiple threads from the same process can be executing linking. Dynamic linking allows a module to include only the simultaneously on multiple processors. As a default, the information needed to locate an exported DLL function at load microkernel uses the policy of soft affinity in assigning threads time or run time. to processors: The dispatcher tries to assign a ready thread to Every process that loads the DLL maps it into its virtual the same processor it last ran on. This helps reuse data still in address space. After the process loads the DLL into its virtual that processor’s memory caches from the previous execution address, it can call the exported DLL functions. The system of the thread. It is possible for an application to restrict its maintains a per-process reference count for each DLL. When a thread execution to certain processors (hard affinity). thread loads the DLL, the reference count is incremented by Thread affinity forces a thread to run on a specific subset of one. When the process terminates, or when the reference count processors. Setting thread affinity should generally be becomes zero, the DLL is unloaded from the virtual address avoided, because it can interfere with the scheduler's ability to space of the process. Like any other function, an exported DLL schedule threads effectively across processors. This can function runs in the context of the thread that calls it. decrease the performance gains produced by parallel Therefore, the following conditions apply: 1) The threads of processing. An appropriate use of thread affinity is testing the process that called the DLL can use handles opened by a each processor. The system represents affinity with a bitmask DLL function. Similarly, handles opened by any thread of the called a processor affinity mask. The affinity mask is the size calling process can be used in the DLL function.