Skip to content
codingtube

codingtube

Coding and Programming tutorials

  • javascript
  • React
  • ES6
  • React js
  • coding
  • ffmpeg
  • java
  • programming
  • information
  • coding
  • Privacy Policy
  • Twitter trends
  • Age Calculatore
  • Codingtube Community
  • YouTube Tags Generator
  • About
  • Toggle search form

Semaphores in operating System

Posted on December 10, 2021December 10, 2021 By christo No Comments on Semaphores in operating System

A semaphore S is an integer variable that, apart from initialization, is accessed only through two standard atomic operations: wait() and signal(). The wait() operation was originally termed P (from the Dutch proberen, “to test”); signal() was originally called V (from verhogen, “to increment”). The definition of wait() is as follows:

wait(S) {
while (S <= 0)
; // busy wait
S--;
}

The definition of signal() is as follows:

signal(S) {
S++;
}

All modifications to the integer value of the semaphore in the wait() and signal() operations must be executed indivisibly. That is, when one process modifies the semaphore value, no other process can simultaneously modify that same semaphore value. In addition, in the case of wait(S), the testing of the integer value of S (S ≤ 0), as well as its possible modification (S–), must be executed without interruption

Table of Contents

  • Semaphore Usage
  • Semaphore Implementation

Semaphore Usage

Operating systems often distinguish between counting and binary semaphores. The value of a counting semaphore can range over an unrestricted domain. The value of a binary semaphore can range only between 0 and 1. Thus, binary semaphores behave similarly to mutex locks. In fact, on systems that do not provide mutex locks, binary semaphores can be used instead for providing mutual exclusion

Counting semaphores can be used to control access to a given resource consisting of a finite number of instances. The semaphore is initialized to the number of resources available. Each process that wishes to use a resource performs a wait() operation on the semaphore (thereby decrementing the count).

When a process releases a resource, it performs a signal() operation (incrementing the count). When the count for the semaphore goes to 0, all resources are being used.

After that, processes that wish to use a resource will block until the count becomes greater than 0

We can also use semaphores to solve various synchronization problems. For example, consider two concurrently running processes: P1 with a statement S1 and P2 with a statement S2. Suppose we require that S2 be executed only after S1 has completed. We can implement this scheme readily by letting P1 and P2 share a common semaphore synch, initialized to 0. In process P1, we insert the statements

S1;
signal(synch);

In process P2, we insert the statements

wait(synch);
S2;

Because synch is initialized to 0, P2 will execute S2 only after P1 has invoked signal(synch), which is after statement S1 has been executed

Semaphore Implementation

To implement semaphores under this definition, we define a semaphore as
follows:

typedef struct {
int value;
struct process *list;
} semaphore;

Each semaphore has an integer value and a list of processes list. When a process must wait on a semaphore, it is added to the list of processes. A signal() operation removes one process from the list of waiting processes and awakens that process

Now, the wait() semaphore operation can be defined as

wait(semaphore *S) {
S->value--;
if (S->value < 0) {
add this process to S->list;
block();
}
}

and the signal() semaphore operation can be defined as

signal(semaphore *S) {
S->value++;
if (S->value <= 0) {
remove a process P from S->list;
wakeup(P);
}
}

The block() operation suspends the process that invokes it. The wakeup(P) operation resumes the execution of a blocked process P. These two operations are provided by the operating system as basic system calls.

operating system Tags:operating system, Semaphores, Semaphores in operating System

Post navigation

Previous Post: Mutex Locks in Operating System
Next Post: Basic Terminology in Data structure

Related Posts

The Critical-Section Problem in Operating System operating system
Recovery in Operating System operating system
Transactional Memory operating system
Process Management operating system
Examples of IPC Systems in Operating System operating system
Peterson’s Solution in operating System operating system

Leave a Reply Cancel reply

You must be logged in to post a comment.

Recent Posts

  • Affiliate Marketing Principles
  • The Basics You Need to Know About Affiliate Marketing
  • Affiliate Marketing Options
  • All About Affiliate Marketing
  • Classification of Database Management Systems
  • Three-Tier and n-Tier Architectures
    for Web Applications
  • Two-Tier Client/Server Architectures for DBMSs
  • Basic Client/Server Architectures in DBMS
  • Centralized DBMSs Architecture in DBMS
  • Tools, Application Environments, and Communications Facilities in DBMS

Categories

  • Affiliate marketing (5)
  • Algorithm (43)
  • amp (3)
  • android (223)
  • Android App (8)
  • Android app review (4)
  • android tutorial (60)
  • Artificial intelligence (61)
  • AWS (3)
  • bitcoin (8)
  • blockchain (1)
  • c (5)
  • c language (105)
  • cloud computing (4)
  • coding (4)
  • coding app (4)
  • complex number (1)
  • Computer Graphics (66)
  • data compression (65)
  • data structure (188)
  • DBMS (44)
  • digital marketing (9)
  • distributed systems (11)
  • ffmpeg (26)
  • game (3)
  • html (6)
  • image processing (35)
  • Inequalities (1)
  • information (4)
  • java (212)
  • java network (1)
  • javascript (9)
  • kotlin (4)
  • leetcode (1)
  • math (21)
  • maven (1)
  • mysql (1)
  • Node.js (8)
  • operating system (109)
  • php (310)
  • Principle Of Mathematical Induction (1)
  • programming (6)
  • Python (4)
  • Python data structure (9)
  • React native (1)
  • React.js (22)
  • Redux (1)
  • seo (4)
  • set (12)
  • trigonometry (6)
  • vue.js (35)
  • XML (3)

sitemap

sitemap of videos

sitemap of webstories

sitemap of website

  • Affiliate marketing
  • Algorithm
  • amp
  • android
  • Android App
  • Android app review
  • android tutorial
  • Artificial intelligence
  • AWS
  • bitcoin
  • blockchain
  • c
  • c language
  • cloud computing
  • coding
  • coding app
  • complex number
  • Computer Graphics
  • data compression
  • data structure
  • DBMS
  • digital marketing
  • distributed systems
  • ffmpeg
  • game
  • html
  • image processing
  • Inequalities
  • information
  • java
  • java network
  • javascript
  • kotlin
  • leetcode
  • math
  • maven
  • mysql
  • Node.js
  • operating system
  • php
  • Principle Of Mathematical Induction
  • programming
  • Python
  • Python data structure
  • React native
  • React.js
  • Redux
  • seo
  • set
  • trigonometry
  • vue.js
  • XML
  • Blog
  • Data compression tutorial - codingpoint
  • How to change mbstring in php 5.6
  • How to diagnose out of memory killed PHP-FPM
  • Introduction to jQuery
  • Privacy
  • Affiliate marketing
  • Algorithm
  • amp
  • android
  • Android App
  • Android app review
  • android tutorial
  • Artificial intelligence
  • AWS
  • bitcoin
  • blockchain
  • c
  • c language
  • cloud computing
  • coding
  • coding app
  • complex number
  • Computer Graphics
  • data compression
  • data structure
  • DBMS
  • digital marketing
  • distributed systems
  • ffmpeg
  • game
  • html
  • image processing
  • Inequalities
  • information
  • java
  • java network
  • javascript
  • kotlin
  • leetcode
  • math
  • maven
  • mysql
  • Node.js
  • operating system
  • php
  • Principle Of Mathematical Induction
  • programming
  • Python
  • Python data structure
  • React native
  • React.js
  • Redux
  • seo
  • set
  • trigonometry
  • vue.js
  • XML
  • Blog
  • Data compression tutorial - codingpoint
  • How to change mbstring in php 5.6
  • How to diagnose out of memory killed PHP-FPM
  • Introduction to jQuery
  • Privacy

© codingtube.tech