Operating Systems Lecture 3: Process Concept

Process Concept

• An operating system runs various programs known as processes.
• A process is defined as a program in execution, requiring sequential progress of instructions.
• Key components of a process include:
  • Program code: Refers to the text section.
  • Current activity: Includes the program counter and processor registers.
  • Stack: Contains temporary data such as function parameters and local variables.
  • Data section: Holds global variables.
  • Heap: Memory allocated dynamically during runtime.

Program vs. Process

• A program is a passive entity stored on disk, whereas a process is active in memory.
• Execution of a program may be initiated through graphical interfaces or command lines.
• One program can correspond to multiple processes, especially with multiple users.

Process State

• A process can exist in several states during its execution:
  • New: The process is being created.
  • Running: Instructions are being actively executed.
  • Waiting: The process is waiting for a specific event.
  • Ready: The process awaits CPU assignment.
  • Terminated: The process has completed its execution.

Process Control Block (PCB)

• PCB contains vital information for each process, known as the task control block:
  • Process state: Status of the process (e.g., running, waiting).
  • Program counter: Points to the next instruction to execute.
  • CPU registers: Stores process-specific register contents.
  • Scheduling information: Includes priorities and pointers to the scheduling queue.
  • Memory-management: Details on memory allocation for the process.
  • Accounting information: Tracks CPU usage and elapsed time since the process started.
  • I/O status information: Lists I/O devices allocated and open files.

Process Scheduling

• Process scheduler is responsible for selecting processes for CPU execution, aiming to maximize CPU use.
• Maintains different queues:
  • Ready queue: Processes ready and waiting in main memory.
  • Wait queues: Processes waiting for events like I/O.

Context Switch

• A context switch occurs when the CPU shifts from executing one process to another.
• Ensures all status data is returned from child to parent processes and deallocates resources used by the process.
• The parent may terminate child processes using the abort() system call for various reasons.

Process Termination

• When a process terminates, all its children may also be terminated, leading to cascading termination.
• Parent processes can wait for child terminations using the wait() system call, which provides status and process id (pid).
• Processes with no waiting parent become zombies, while those whose parent terminated without wait become orphans.

Interprocess Communication (IPC)

• Processes can be independent or cooperating, with cooperating processes sharing data and affecting each other.
• Reasons for cooperation include information sharing, computation speedup, modularity, and convenience.
• Two models for IPC:
  • Shared memory: Processes communicate through a designated area of memory.
  • Message passing: Processes exchange messages without shared variables.

Producer-Consumer Problem

• A common example of cooperating processes involves a producer creating information consumed by a consumer.
• Variations:
  • Unbounded-buffer: No practical limit on buffer size; the producer never waits.
  • Bounded-buffer: Fixed buffer size; the producer waits if the buffer is full.

IPC: Shared Memory

• Communication management is controlled by user processes rather than the operating system.
• Synchronization issues arise when processes access shared memory.

IPC: Message Passing

• Processes communicate without shared variables.
• Requires establishing communication links and exchanging messages, either fixed or variable in size.

Android Process Hierarchy

• Mobile operating systems like Android manage processes based on importance, with specific types ranked from most to least important:
  • Foreground process
  • Visible process
  • Service process
  • Background process
  • Empty process

Multitasking in Mobile Systems

• Early mobile systems allowed only one active process, suspending others.
• Starting from iOS4, limited multitasking was introduced:
  • Single foreground process is user-controlled.
  • Multiple background processes allowed with specified limitations.
• Subsequent iOS versions support richer multitasking, including split-screen functionality on larger devices.

This quiz covers the fundamental concepts of processes in operating systems, detailing what defines a process and its components. Explore how programs execute in a sequential manner and the various parts that constitute a process. Perfect for anyone studying the basics of operating systems.