OS ITO

• Cooperating process


  A process that can affect or be affected by other processes executing in the system
• Cooperating processes


  • Can directly share a logical address space (that is, both code and data)
  • Can share data only through files or messages
• Operating system with multiple processes

  1. Processes run together independently

  2. Act as a bridge between the user and hardware for sharing information
• Types of processes in an operating system

  • Independent process: Processes whose task is not dependent on any other processes
  • Cooperating process: Processes that depend on other processes and work together to achieve a common task
• Advantages of cooperating processes


  • Resource sharing
  • Improved responsiveness
  • Enhanced efficiency
  • Better utilization of hardware
  • Increased throughput
• Disadvantages of cooperating processes


  • Complexity
  • Resource competition
  • Security risks
  • Overhead
  • Difficulty in debugging
• Methods of cooperating processes


  • Cooperation by sharing
  • Cooperation by message passing
• Cooperation by sharing


  1. Processes interact with each other to share resources

  2. Critical section: Allows only one process at a time to enter and access/manipulate the shared resources
• Cooperation by message passing


  1. Processes communicate by passing messages

  2. Producer process creates a message and transfers it to the kernel

  3. Kernel passes the message to the receiving process
• Inter-process communication (IPC)


  A cornerstone of modern operating systems, allowing processes to collaborate, share data, and synchronize their activities
• Options to implement IPC

  • Pipes
  • Message queues
  • Semaphores
  • Shared memory

  
• Inter-process communication methods


  1. Shared memory

  2. Message passing

  
• Shared memory: Producer-consumer problem


  1. Producer produces items and stores them in a shared buffer

  2. Consumer consumes items from the shared buffer

  3. Unbounded buffer problem: No limit on buffer size

  4. Bounded buffer problem: Buffer has a certain capacity

  
• Message passing


  1. Processes communicate without using shared memory

  2. Establish communication link

  3. Exchange messages using send() and receive() primitives

  4. Message can have header and body

  
• IPC systems


  • POSIX (Portable Operating System Interface): uses shared memory
  • Mach: uses message passing
  • Windows XP: uses message passing using local procedural calls

  
• Direct communication


  Processes explicitly name the recipient or sender of the communication
• Indirect communication


  Messages are sent to and received from mailboxes
• Process communication in client-server environment

  • Exchange of data and services among multiple machines or processes
  • One process acts as a client requesting a service or data, and another acts as a server providing those services or data

  
• Ways of client-server communication

  • Sockets mechanism
  • Remote procedure call
  • Message passing
  • Inter-process communication
  • Distributed file systems

  
• Sockets mechanism


  • End points of communication between two machines
  • Provide a way for processes to communicate, either on the same machine or over the Internet
• Remote procedure call (RPC)


  Protocol that allows a client to execute a procedure call on a remote server, as if it is a local procedure call
• Message passing


  Communication method where machines communicate by sending and receiving messages

  This approach is commonly used in Parallel and Distributed System
• Inter-process communication (IPC)


  • Allows communication between processes within the same machine
  • Enables data sharing and synchronization between different processes
• Distributed file systems


  • Provide access to files from multiple machines in a network
  • Client can access and manipulate files stored on a remote server through a standard interface
• Process


  • An instance of a program that is being executed by the operating system
  • Represents an independent unit of work with its own memory space, program counter, and system resources
• Process control block (PCB)


  • A data structure used by the operating system to store and manage information about a process
  • Acts as a repository for all the necessary information required to manage a process effectively
• Key components of a PCB

  • Process state
  • Process ID
  • Program counter
  • CPU registers
  • CPU scheduling information
  • Memory management information
  • Accounting information
  • I/O status information
• Process


  An instance of a program that is being executed by the operating system. It represents an independent unit of work with its own memory space, program counter, and system resources.
• Process concepts


  Understanding the lifecycle of a process, its states, and the mechanisms used by the operating system to manage and control processes effectively.
• Process Control Blocks (PCBs)


  A vital component for an operating system to manage processes effectively. It acts like a central hub, storing all essential information regarding a particular process.
• Process Control Block (PCB)


  A data structure used by the operating system to store and manage information about a process.
• Key Components of a PCB

  • Process State
  • Process ID
  • Program Counter
  • CPU Registers
  • Memory Information
  • Process Scheduling Information
  • Accounting Information
• Advantages of Using Process Control Block

  • Lets the operating system execute different tasks like process scheduling, context switching
  • Helps in scheduling the processes and ensures efficient CPU resource allocation
  • Helps in efficient resource utilization and resource sharing
  • Helps the OS to save the process state which helps in Context switching
• Disadvantages of using Process Control Block

  • Significant usage of memory to store PCB for each process
  • Reduces the scalability of the process in the OS due to added complexity
• Importance of PCBs
• Typical Process Creation process

  1. System Call: The existing process (parent process) initiates a system call to request creation of a new process

  2. Process Creation: The operating system allocates resources for the new process (child process)

  3. PCB Creation: A new Process Control Block (PCB) is created to manage the child process

  4. Process State and Resources: The child process inherits a copy of the parent process's memory space and some resources

  5. Process Divergence: After creation, the child process typically starts executing from the same point in the program code as the parent process, but they can diverge
• Importance of Process Creation

  • Multitasking: Allows the operating system to run multiple programs concurrently
  • Modular Programming: Complex tasks can be broken down into smaller processes
  • Responsiveness: Processes can be created to handle user requests or system events promptly
• Process State Transitions


  1. New -> Ready: When the OS allocates memory and resources to the new process, it transitions to the ready state

  2. Ready -> Running: The process scheduler selects a process from the ready queue to be assigned the CPU

  3. Running -> Ready: The OS might preempt the running process due to factors like priority or time-sharing algorithms

  4. Running -> Blocked/Waiting: If the running process issues an I/O request or encounters a resource unavailable

  5. Blocked/Waiting -> Ready: Once the awaited event occurs, the process transitions back to the ready state

  6. Running -> Exit/Terminated: A process might directly terminate from the ready or waiting state
• Advantages and Disadvantages of the five-state process model

  • Advantages: The New and Exit states are very useful components for process management. It is a more efficient implementation of the preceding two-state process concept.
  • Disadvantages: The data of a process that is terminated or exited from the OS is not saved by the OS. When each process enters a blocked state, the processor remains idle until at least one process exits the waiting state, which might cause a performance issue.
• Process Termination


  1. Process Cleanup: Release any resources held by the process

  2. Update PCB: Update the process state in the PCB to reflect the termination

  3. Release PCB: Remove the PCB from the system's list of active processes

  4. Signal Termination: Notify the parent process or any other interested processes about the termination

  5. Return Exit Status: Provide an exit status or code to the parent process