Processes in Operating Systems (Os) with Examples

• When a program is loaded into memory and starts running, it becomes a process.
• Each process has its own memory space, resources, and execution state.
• A process is a fundamental concept in operating systems.
• Each process is independent, isolated, and has its own memory space, which prevents it from interfering with other processes.

Components of a Process

Stack

• The stack is like a temporary scratchpad used by a process.
• It stores function calls, local variables, and execution context.
• When a function is called, a new stack frame is added, and when the function ends, its frame is removed.
• Think of the stack as a pile of plates. Each time you add a plate (function call), it goes on top.
• When you finish with a plate (function ends), you take it off the top.
• This last-in, first-out (LIFO) structure mirrors how the stack operates in a process.

Heap

• The heap is a dynamic storage area where a process can allocate memory during runtime.
• It's like an expandable workspace where a process can request and release memory as needed.
• Consider the heap as a desk with papers. A process can ask for more papers (memory) when it needs them and return them when done.

Text

Data

• The data section holds global and static variables used by the program. It includes initialized and uninitialized data.
• Functions can write and read information in the data section to communicate and share important details, ensuring coordination during the process execution.

Process vs Program

• A program is a set of instructions written in a programming language.
• When a program is loaded into memory and starts running, it becomes a process.
• Each process has its own memory space, resources, and execution state.

Process Life Cycle

• New: The process is being created.
• Ready: The process is ready to execute but is waiting for CPU time.
• Running: The process is actively executing on the CPU.
• Blocked: The process is waiting for an event, such as I/O completion.
• Terminated: The process has finished its execution.

Schedulers in Os

• In operating systems, schedulers are responsible for determining the order in which processes are executed by the CPU.
• The three main types of schedulers are:

Long-Term Scheduler (Job Scheduler)

• The long-term scheduler selects processes from the job pool (a pool of processes waiting to be brought into memory) and loads them into the main memory for execution.
• Its primary goal is to control the degree of multiprogramming, balancing the number of processes in the ready queue.
• Example: Consider a system where new processes arrive from user submissions.
• The long-term scheduler decides which processes to bring into memory based on factors like priority, system load, etc.

Short-Term Scheduler (CPU Scheduler)

• The short-term scheduler selects processes from the ready queue and allocates the CPU to them for a short time.
• It is responsible for determining the order in which ready processes are executed, providing a fair and efficient utilization of the CPU.
• Example: In a system with multiple processes in the ready queue, the short-term scheduler decides which process to run next based on priority,
• time quantum (for time-sharing systems), or other scheduling algorithms.

Medium-Term Scheduler

• The medium-term scheduler decides when to swap processes in and out of the main memory.
• It is responsible for managing processes in the "waiting" or "blocked" state, moving them out of the main memory to secondary storage.
• when necessary and bringing them back when their execution can continue.
  

What is Process Scheduling?

• Process scheduling is a critical component of operating systems that determines which process to execute next on the CPU.
• The goal is to efficiently utilize the CPU while providing fair and responsive execution to all processes.

Scheduling Algorithms

• First-Come, First-Served (FCFS)
• Shortest Job First (SJF):
• Round Robin:
• priority Scheduling:
• Multilevel Queue:

1. First-Come, First-Served (FCFS)

2. Shortest Job First (SJF)

3. Round Robin

4. Priority Scheduling:

5. Multilevel Queue:

Examples

• In a real-time system, processes related to critical tasks like engine control are assigned higher priority to ensure they get immediate
• CPU time, while less critical tasks like logging run at lower priority to avoid disrupting critical operations.

Process Creation

• Forking
• Executing
• Spawning

Forking

• In Unix-like systems, a process can create a new process using the fork() system call.
• The new process is a copy of the parent process with a different process ID (PID).

Executing

Spawning

Example 1:

• Consider a word processing application.
• When you open the application, it creates a process to manage the user interface.
• If you open multiple documents simultaneously, each document is handled by a separate process, ensuring that a crash in one document does not affect others.

Example 2:

• Web browsers like Google Chrome run multiple processes, one for each tab or extension.
• This isolation ensures that a misbehaving website or extension does not crash the entire browser.

Process Control Block (PCB)

• A Process Control Block (PCB) is a data structure that contains all the information about a process, including its state, program counter, registers, and more.
• It is used by the operating system to manage and schedule processes.

Inter Process Communication (IPC)

• Processes often need to communicate with each other.
• IPC mechanisms like pipes, sockets, and shared memory allow processes to exchange data and synchronize their activities.

Process Termination

• In a multitasking environment, when a process is waiting for user input, it enters the "Blocked" state, allowing other processes to utilize the CPU.
• Once the input is available, it transitions back to the "Ready" state.
• In a server application, multiple processes handle incoming client requests.
• These processes communicate through sockets, allowing them to share data and coordinate their responses.

When Does Context Switching Happen?

• Context switching occurs in operating systems when the CPU switches from executing one process to another.
• This switch happens in various situations, such as when a running process voluntarily turns over the CPU (e.g., due to a system call or waiting for I/O)
• or
• when the operating system's scheduler preempts the currently running process to give CPU time to another process.

Attributes or Characteristics of a Process

Program Counter (PC)

• The program counter is like a "pointer" that tells the CPU which instruction in a program to execute next.
• In the context of processes, each process has its own program counter.
• This means that different processes can be running different parts of a program simultaneously without interfering with each other.

• Imagine two people reading different books. Each person has their own bookmark (program counter).
• They can read their books independently, and their bookmarks help them keep track of where they left off.

Registers

• Registers are small, high-speed storage areas inside the CPU. Each process has its own set of registers.
• These registers store important data and execution context, such as the values of variables, function call information, and other critical details.
• By having separate registers, processes can work on their data without mixing it up with other processes.

Example:

• Think of registers as personal notebooks. In a classroom, each student has their own notebook (registers) where they write down their notes and ideas.
• This way, they can take notes without sharing a common notebook with others.

Memory Space

• Processes have their own dedicated memory space.
• This means that the data and variables used by one process are stored separately from those used by other processes.
• This separation ensures that one process cannot accidentally or maliciously access or modify the memory of another process, providing data isolation.

Example:

• Picture a shared kitchen with different cabinets.
• Each person (process) has their own cabinet (memory space) to store their food.
• This way, nobody can take food from someone else's cabinet, ensuring that each person's food is safe and isolated.

File Descriptors

• Processes have separate file descriptors, which are like handles that allow them to access files.
• These file descriptors ensure that one process's interaction with files does not interfere with another process's access to the same files.
• It's like having a dedicated key to your own room in a building.

Example:

• In an office building, each employee has a unique key (file descriptor) to their office (file).
• They can access their office without needing someone else's key. This way, privacy and security are maintained.

Status Information

• Each process maintains information about its current state, such as whether it's running, waiting, or ready to execute.
• This status information helps the operating system manage and schedule processes effectively.

Conclusion