During my recent exploration of “Operating System Concepts with Java,” I delved into Chapter 4, focusing on process scheduling—an area integral to our work as software developers. This chapter provides a comprehensive view of how operating systems manage this critical task.
It's always enriching to deepen your understanding of familiar topics. I'll be sharing a summary and a diagram illustrating the process, along with a snapshot of the book. Join me in exploring these insights, fellow programmers!
4.2 Process Scheduling
Process scheduling is a fundamental aspect of operating systems that aims to maximize CPU utilization and provide efficient execution of processes. Here’s an overview of the key concepts related to process scheduling:
Objectives of Process Scheduling:
1.Multiprogramming: Ensure that at least one process is running at all times to maximize CPU utilization.
- Time Sharing: Switch the CPU among processes frequently enough to allow users to interact with each program effectively.
Scheduling Queues:
As processes enter the system, they are managed through various queues:
-
Job Queue: Contains all processes in the system, including those waiting to be admitted to the system.
-
Ready Queue: Contains processes that are residing in main memory and are ready and waiting to execute. This queue is typically implemented as a linked list, where each PCB points to the next PCB in the queue.
-
Device Queues: Each I/O device has its own queue containing processes waiting for access to that device. For example, a disk device queue would hold processes waiting for disk I/O operations to complete.
Process State Transitions:
-
Dispatching: When a process is selected from the ready queue to be executed on the CPU.
-
I/O Request: If a process issues an I/O request, it moves from the running state to the waiting state and enters the corresponding device queue.
-
Subprocess Creation: If a process spawns a new subprocess, it may wait for the new subprocess to terminate before returning to the ready queue.
-
Interrupt Handling: Processes can be forcibly removed from the CPU due to interrupts (e.g., timer interrupts, I/O interrupts), causing them to be put back into the ready queue after handling the interrupt.
Process Lifecycle:
-
Execution: A process executes on the CPU until it either completes its task, waits for an event (e.g., I/O completion), or is interrupted.
-
Terminatio: When a process finishes its execution, it is removed from all queues, its PCB and resources are deallocated, and it transitions to the terminated state.
Queueing Diagram:
A queueing diagram illustrates the flow of processes between different queues (ready queue, device queues) and the resources that serve them (CPUs, I/O devices). This visual representation helps in understanding how processes move through the system during scheduling.