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Threads in Operating System

Last Updated on April 18, 2023 by Prepbytes

Operating Systems is one the most asked topics in the Technical Interviews of top Product Based Companies for the role of Software Developers, Testers, and System Engineers. One of these essential topics is threads in operating systems. We will be discussing the Threads in Operating System along with their components, need, types, advantages, and disadvantages.

What is a Thread?

In computing, a thread is a small unit of processing that runs independently within a program. Threads are essential in programming languages because they enable developers to write concurrent and parallel applications that can perform multiple tasks simultaneously.

What are Threads in Operating Systems?

Threads are an essential component of modern operating systems. Threads in Operating Systems help to increase the performance of the applications as well as the entire system. A Thread is a smaller unit of execution within a process that shares the same memory and resources. Threads can be created and managed by the operating system or the application itself. Threads can be implemented in various different ways in an Operating System.

The image given below shows the threads of a single process in an operating system.

Components of Threads in Operating System

The Threads in Operating System have the following three components.

  • Stack Space
  • Register Set
  • Program Counter

Why do we need Threads in Operating Systems?

Threads offer several advantages in the operating system, resulting in improved performance. Some reasons why threads are necessary for the operating system include:

  • Threads use the same data and code, reducing operational costs between threads.
  • Creating and terminating threads is faster than creating or terminating processes.
  • Context switching in threads is faster than in processes.

Why Multithreading is needed in Operating Systems?

Multithreading involves dividing a single process into multiple threads instead of creating a new process, in order to achieve parallelism and improve performance. This approach provides several advantages that include,

  • Resource sharing among threads, increased program responsiveness even if some parts of the program are blocked, and improved economy compared to creating separate processes.
  • By sharing resources within a single process, threads can work more efficiently than processes, which can be costly to create and manage.

Process vs Thread

The given table summarizes the differences between the threads and Processes in the Operating system.

Process Thread
Definition An independent program with its own memory space and resources A lightweight unit of execution within a process, sharing the same memory space
Creation Created by the operating system when a program is launched Created by the program itself
Memory Each process has its own memory space, including its own stack, heap, and code segment Threads within a process share the same memory space, including stack and heap
Communication Inter-process communication is necessary for processes to communicate Threads within a process can communicate directly through shared memory
Resource allocation Processes are allocated system resources, including memory and I/O resources Threads share the same resources as the process they belong to
Control Each process runs independently and can be controlled separately Threads within a process share the same control flow and can communicate directly
Overhead Processes have a higher overhead due to the need for inter-process communication and separate memory space Threads have lower overhead due to shared memory space and direct communication capabilities
Parallelism Processes can run in parallel on different processors Threads within a process can also run in parallel on different processors

Types of Threads in Operating System

Threads in Operating System are of the following two types.

  1. User-level Threads in Operating System
  2. Kernel Level Threads in Operating System
  • User-level threads in Operating System
    User-level threads are not recognized by the operating system and are implemented by the user. If a user-level operation causes thread blocking, the entire process is blocked. Kernel-level threads do not interact with user-level threads. Instead, user-level threads are treated by the kernel as single-threaded processes. Implementing user-level threads is a straightforward process.

    Advantages of User-Level Threads in Operating Systems
    The following are some of the advantages of User-Level Threads in Operating Systems.

    • User-level threads are highly efficient and have fast switching times that are comparable to procedural calls.
    • They do not require intervention from the operating system and offer great flexibility, making them adaptable to the specific needs of an application.

    Disadvantages of User-Level Threads in Operating Systems
    User-Level Threads in Operating Systems also have the following disadvantages.

    • Since the operating system is not aware of user-level threads, it cannot effectively schedule them.
    • If a user-level thread performs a blocking operation, the entire process will be blocked.
    • User-level threads cannot fully utilize multi-core processors, as only one thread can run on a single core at any given time.
  • Kernel-level Threads in Operating System
    The operating system manages and supports kernel-level threads. These threads are controlled by the kernel, which provides more visibility and control over thread execution. However, this increased control and visibility come with a cost, including higher overhead and potential scalability problems.

    Advantages of Kernel-level threads in Operating System
    The Advantages of Kernel-Level Threads in Operating Systems are given below.

    • Kernel-level threads in Operating Systems are fully recognized and managed by the kernel, which enables the scheduler to handle them more efficiently.
    • Since kernel-level threads are managed directly by the operating system, they provide better performance compared to user-level threads. The kernel can schedule them more efficiently, resulting in better resource utilization and reduced overhead.
    • If a kernel-level thread is blocked, the kernel can still schedule another thread for execution.

    Disadvantages of Kernel-level threads in Operating System
    Kernel-Level Threads in Operating Systems have the following disadvantages.

    • Compared to user-level threads in Operating System, creating and managing kernel-level threads is slower and less efficient. The overhead associated with kernel-level threads is that it requires a thread control block, which contains information about the thread’s state and execution context.
    • Creating and managing these control blocks can lead to resource wastage and scheduling overhead, which can make kernel-level threads less efficient in terms of system resources.

Advantages of Threading

The advantages of Multithreading in an application are given below.

  • A software application that uses multiple threads can respond more quickly to user input.
  • Application with Multithreading can also share resources such as code and data between threads, allowing for several activities to occur simultaneously.
  • In addition, running threads in parallel on different processors can increase concurrency in a machine with multiple processors.
  • Compared to processes, creating and switching between threads is less expensive and takes less time. Therefore, threads have a shorter context-switch time than processes.

Issues with Threading

Multithreading also faces the following drawbacks.

  • When multiple threads access shared resources or perform operations that rely on the order of execution, issues such as race conditions, deadlocks, and synchronization problems may arise.
  • Multithreading can also make debugging and testing more difficult and lead to performance problems due to overhead and competition for system resources.

Thus it is crucial to thoroughly plan and test multithreaded applications to prevent these problems.

In conclusion, threads are a vital component of modern operating systems, and they play a significant role in improving the performance of applications and the overall system. There are two types of threads in an operating system: user-level threads and kernel-level threads. Each type of thread offers its own advantages and disadvantages, and the choice of which type to use depends on the application’s specific requirements. While threading offers several advantages over single-threaded applications, it also has several issues that need to be addressed to ensure efficient and reliable application performance.

Frequently Asked Questions(FAQs)

Here are some Frequently Asked Questions related to “Threads in Operating System”.

Ques 1. What are the benefits of using threads in operating systems?
Ans. Threads can improve performance, reduce resource consumption, and enable better resource sharing and responsiveness.

Ques 2. What are the different types of threads in operating system?
Ans. There are two main types of threads: user-level threads and kernel-level threads.

Ques 3. What is the difference between user-level and kernel-level threads in Operating Systems?
Ans. User-level threads are managed by the user-level program, while kernel-level threads are managed by the operating system.

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