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Articles by Arnab Chakraborty
Page 170 of 377
Scheduler activations
Scheduler activations is a technique that enables effective communication between the user-thread library and the kernel. This mechanism provides an elegant solution to the problem of managing user threads efficiently while maintaining kernel awareness of thread activities. How Scheduler Activations Work The kernel provides an application with a set of virtual processors (also called Lightweight Processes or LWPs). The application can then schedule user threads onto these available virtual processors. The key innovation is that the kernel must inform the application about certain critical events through a mechanism called upcalls. Scheduler Activations Architecture ...
Read MoreLightweight process (LWP)
Many systems implement either the many-to-many or the two-level model by placing an intermediate data structure between user and kernel threads. This data structure is typically known as a Lightweight Process (LWP) and serves as a virtual processor for scheduling user threads. How Lightweight Processes Work To the user-thread library, the LWP appears to be a virtual processor on which the application can schedule a user thread to run. Each LWP is attached to a kernel thread, and it is the kernel threads that the operating system schedules to run on physical processors. ...
Read MoreData structures of a Windows thread
Windows implements the Windows API, which is the primary API for the family of Microsoft operating systems (Windows 98, NT, 2000, XP, and Windows 7). A Windows application runs as a separate process, and each process may contain one or more threads. Additionally, Windows uses the one-to-one mapping, where each user-level thread maps to an associated kernel thread. Components of a Windows Thread The general components of a thread include − A thread ID uniquely identifying the thread A set of registers representing the status of the processor A user stack, employed when the thread is ...
Read MoreHardware Synchronization
Hardware Synchronization provides solutions to the critical-section problem using atomic hardware instructions. These hardware-based techniques form the foundation for more sophisticated synchronization mechanisms and offer better performance than pure software solutions. Hardware synchronization relies on the premise of locking using atomic operations that cannot be interrupted. These instructions allow us to test and modify memory locations or swap values as one uninterruptible unit, making them ideal for implementing mutual exclusion in multiprocessor environments. Why Hardware Support is Needed In uniprocessor systems, disabling interrupts can solve the critical-section problem by preventing preemption. However, this approach fails in multiprocessor ...
Read MorePeterson's Problem
Peterson's solution provides a good algorithmic description of solving the critical-section problem and illustrates some of the complexities involved in designing software that addresses the requirements of mutual exclusion, progress, and bounded waiting. Peterson's Algorithm Peterson's solution is restricted to two processes that alternate execution between their critical sections and remainder sections. The processes are numbered P0 and P1. We use Pj to denote the other process when Pi is present; that is, j = 1 - i. Shared Data Variables Peterson's solution requires the two processes to share two data items: int turn; ...
Read MoreResuming Process Monitoring for a Process Instance
When multiple processes are suspended on a condition variable x and an x.signal() operation is executed, we must determine which suspended process should be resumed next. A simple solution uses first-come, first-served (FCFS) ordering, where the longest-waiting process is resumed first. However, this approach is often inadequate for complex scheduling requirements. Conditional-Wait Construct The conditional-wait construct provides a more sophisticated scheduling mechanism with the form: x.wait(c); Here, c is an integer expression evaluated when the wait() operation executes. The value of c, called a priority number, is stored with the suspended process name. When ...
Read MoreDifference between Deadlock Prevention and Deadlock Avoidance
Deadlock prevention and avoidance are crucial techniques in operating systems to ensure continuous operation without system-wide halts. Deadlocks can cause data loss, system downtime, and reduced productivity, making these techniques essential for maintaining system availability and reliability. What is Deadlock? A deadlock is a situation where two or more processes are unable to proceed because they are waiting for each other to release resources. This creates a circular dependency where processes remain stuck in a waiting state, causing a system-wide halt. Deadlock occurs when four conditions are met simultaneously: mutual exclusion, hold and wait, no preemption, and circular ...
Read MoreProgram execution in CPU
One may be amazed how the CPU is programmed. A special register is contained in CPU − the instruction register − whose bit pattern determines what the CPU will do. Once that action has been completed, the bit pattern in the instruction register can be changed, and the CPU will perform the operation specified by this next bit pattern. Most of the modern CPUs use an instruction queue. Some instructions are waiting in the queue, ready to be executed. Different electronic circuitry keeps the instruction queue full while the control unit is executing the instructions. But this is simply ...
Read MoreProcess Communication in Operating System
Processes executing concurrently in an operating system can be classified as independent processes or cooperating processes. An independent process cannot affect or be affected by other processes in the system and does not share data with any other process. A cooperating process can affect or be affected by other processes and shares data with them. Why Process Cooperation is Important Operating systems provide environments that support process cooperation for several key reasons: Information sharing − Multiple users may need concurrent access to the same information, such as shared files or databases. Computation speedup − Tasks can ...
Read MoreGarbage collection(GC) in JavaScript?
Memory management in JavaScript is much easier than in low-level languages like C or C++. Unlike low-level languages, JavaScript automatically detects which objects will be needed in later cases and which will be garbage that is occupying memory without any reason. In this article, we shall discuss how garbage collection (GC) works in JavaScript. There are a few important parts that we are going to discuss in detail: Reachability from root Interlinked Objects (interconnections between different objects) Unreachable Collections (Broken link) Reachability The first concept of ...
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