Process Management and Scheduling Overview

Process

An active instance of a program in execution, including its state, data, and interactions. It is not just the code of the program.

Multiprogramming

Running multiple processes by rapidly switching the CPU between them.

Multiprocessing

Using multiple CPUs or CPU cores to run code simultaneously.

Multithreading

Running different parts of the same process concurrently on multiple CPUs.

Multitasking

A general term encompassing multiprogramming, multiprocessing, and multithreading.

Operating System (OS) Tasks

Managing processes, allocating resources, preventing deadlocks, supporting interprocess communication, and allowing users to create new processes.

Process Creation

Triggered by system initialization, execution of a process creation system call, a user request, or the initiation of a batch job. The fork() function creates a child process.

Process Suspension

Occurs when a process waits for I/O, data, or a signal from another process, or when it voluntarily pauses or is forced to pause by the OS.

Process Termination

Caused by normal exit, error exit, fatal errors, operator intervention, parent process request, or timeout.

Running

The process is actively using the CPU.

Ready

The process is runnable but currently stopped to allow another process to run.

Blocked

The process is unable to run until an external event occurs.

New

The process has just been created but is not yet in the 'ready' pool.

Exit

The process has been completed.

Process Control Block (PCB)

A data structure containing process ID, state, control, resource ownership, memory management, and accounting information.

Interrupts

Events that cause a change in the normal flow of a process's execution, often triggered by external devices needing CPU access.

Context Switch

Saving the current process's context (CPU registers) when an interrupt occurs, before executing an interrupt handler and potentially switching to a new process.

Threads

A stream of execution within a process, considered a lightweight process, that can share process memory and resources.

Thread Pooling

A set number of threads are created based on CPU cores, and tasks are assigned to run on available threads.

Inter-Process Communication (IPC)

Techniques for processes to communicate, exchange data, resolve resource conflicts, and manage dependencies.

Process Scheduling

The OS decides which process will run next, which can be achieved via timer interrupts (pre-emptive) or when a process yields (cooperative). Scheduling is required on process exit or when a process blocks on I/O.

First-Come First-Served (FCFS)

Processes are added to a queue in the order they arrive. The process at the head of the queue runs until it blocks. The blocked process then joins the tail of the queue when ready.

FCFS Example

If processes P0, P1, P2, and P3 arrive in that order with processing times of 7ms, 5ms, 9ms, and 6ms, respectively, then they are processed in that order.

Shortest Job First (SJF)

Processes are ordered by their run-time duration. The process with the shortest run time is executed first.

SJF Example

Using the same processes, P1 is processed first (5ms), then P3(6ms), then P0(7ms), then P2 (9ms).

Round Robin (RR)

Each process is allocated a time slice (quantum). After its quantum, the process moves to the end of the queue.

RR Example

Using the same processes, with a quantum of 4ms and a 0 switch time, P0 is processed first for 4ms, then P1, P2 and P3. P0 then continues with its remaining 3ms, P1 needs just 1ms to complete, and so on until completion.

Priority Scheduling

Each process is assigned a priority. The process with the highest priority is executed first.

FCFS Note

FCFS is simple, but can lead to longer waiting and processing times for some processes.

SJF Note

SJF minimizes wait time, but long-running processes may 'starve'. It also requires predicting the future duration of jobs.

RR Note

RR ensures fairness by equally distributing processing time.

Priority Scheduling Note

Useful when priority is required but may cause low priority processes to starve.