operating systems unit 2 study guides

What's Process Management?

• Fundamental component of operating systems involves managing processes and their execution
• Processes represent running programs or applications that require system resources (CPU time, memory)
• Process management tracks process state, resource usage, and execution order
• Ensures fair allocation of system resources among competing processes
• Provides mechanisms for processes to communicate and synchronize with each other
• Implements scheduling algorithms to determine which process runs next on the CPU
• Handles process creation and termination, along with any associated cleanup tasks

Key Concepts in Process Management

• Process represents an instance of a running program, identified by a unique process ID (PID)
• Process control block (PCB) stores metadata about each process (state, CPU registers, memory limits, open files)
• Context switching saves the state of the current process and loads the saved state of another process
• Scheduling determines which process runs next based on factors like priority, CPU burst time, and arrival time
• Interprocess communication (IPC) enables processes to exchange data and synchronize their execution
• Shared memory allows multiple processes to access the same memory region for efficient IPC
• Signals provide a way for the OS or other processes to send notifications to a process

Process States and Lifecycle

• New: Process is being created, PCB is initialized, but not yet added to the ready queue
• Ready: Process is waiting to be assigned to a CPU, loaded into memory and ready to execute
• Running: Instructions are being executed by the CPU, process is actively consuming resources
• Waiting (Blocked): Process is waiting for some event to occur (I/O completion, signal, resource availability)
  • Transition to waiting state occurs when process makes a system call or is interrupted by the scheduler
• Terminated: Process has finished execution or has been aborted, releases all acquired resources
• Suspended Ready: Process is in secondary storage (swapped out) but ready to execute once loaded into memory
• Suspended Waiting: Process is in secondary storage and waiting for an event before it can resume execution

Process Scheduling Algorithms

• First-Come, First-Served (FCFS): Non-preemptive, processes are executed in the order they arrive
• Shortest Job Next (SJN): Non-preemptive, selects the process with the shortest next CPU burst
• Priority Scheduling: Each process is assigned a priority, highest priority process is executed first
  • Preemptive version allows the current running process to be interrupted by a higher-priority process
• Round Robin (RR): Preemptive, each process is given a fixed time quantum to execute before being preempted
• Multilevel Queue: Ready queue is partitioned into separate queues, each with its own scheduling algorithm
• Multilevel Feedback Queue: Allows processes to move between queues based on their behavior and CPU bursts

Inter-Process Communication

• Shared Memory: Multiple processes can access a common memory region for fast data exchange
  • Requires synchronization mechanisms (locks, semaphores) to prevent race conditions
• Message Passing: Processes send messages to each other through communication channels (pipes, sockets)
  • Useful for exchanging small amounts of data or control signals between processes
• Pipes: Unidirectional communication channels, data written by one process is read by another
  • Named pipes (FIFOs) can be used for communication between unrelated processes
• Sockets: Bidirectional communication endpoints, support both local and remote inter-process communication
• Remote Procedure Calls (RPC): Allows a process to execute a procedure in another address space (local or remote)

Process Synchronization

• Race Condition: Occurs when multiple processes access shared data concurrently, leading to unpredictable results
• Critical Section: Code segment where a process accesses shared resources, must be executed atomically
• Mutex Locks: Ensures mutual exclusion by allowing only one process to enter a critical section at a time
• Semaphores: Generalized synchronization mechanism, can be used for resource counting and process coordination
  • Binary semaphores (mutexes) are used for mutual exclusion, counting semaphores track resource availability
• Monitors: High-level synchronization construct that encapsulates shared data and provides safe access methods
• Deadlock: Situation where two or more processes are unable to proceed because each is waiting for the other to release a resource
  • Occurs when four conditions hold simultaneously: mutual exclusion, hold and wait, no preemption, circular wait

Common Process Management Issues

• Starvation: A process is perpetually denied necessary resources, unable to make progress
  • Can occur in priority scheduling if low-priority processes are constantly bypassed by higher-priority ones
• Priority Inversion: A high-priority process is indirectly preempted by a lower-priority process
  • Happens when the high-priority process is waiting for a resource held by the low-priority process
• Convoy Effect: A convoy of processes is formed when multiple processes are waiting for a resource held by a slow process
• Thrashing: Excessive paging/swapping activity due to insufficient main memory to hold all active processes
  • Results in significant performance degradation as more time is spent on paging than actual execution
• Orphan Processes: Processes whose parent has terminated without waiting for the child to finish or explicitly killing it
• Zombie Processes: Terminated processes whose exit status has not been collected by the parent process

Real-World Applications

• Operating Systems: Process management is a core component of all modern operating systems (Windows, Linux, macOS)
• Web Servers: Handle multiple client requests concurrently, each request is processed in a separate thread or process
• Database Management Systems: Use process and thread management to handle concurrent queries and transactions
• Scientific Simulations: Often involve parallel processing, requiring careful coordination and synchronization between processes
• Embedded Systems: Manage real-time processes and threads with strict timing constraints (automotive, avionics)
• Distributed Computing: Involves managing processes across multiple nodes in a cluster or grid environment
• Mobile Apps: Utilize process and thread management to handle user interactions, background tasks, and system events