Understanding Operating Systems: Processes, Threads, and Scheduling
Operating System Concepts
Processes and Threads
Process Fundamentals
A process is a program in execution. It’s dynamic and active, unlike a static program. Each process has components like code, data, stack, and heap.
Threads and Multithreading Models
Threads exist within a process and share resources like code, data, and heap. Each thread has its own stack, registers, and program counter. There are three main multithreading models:
- One-to-One: Each user thread maps to a kernel thread.
- One-to-Many: Multiple user threads map to a single kernel thread.
- Many-to-Many: Multiple user threads map to multiple kernel threads.
The Many-to-One model has limitations. It can cause blocking system calls to affect the entire process and doesn’t allow parallel execution on multi-processors.
Context Switching
Context switching is the process of the CPU changing from one task to another without conflicts. It involves saving the current task’s state and loading the next task’s state.
CPU Scheduling
Scheduling Algorithms
Various CPU scheduling algorithms exist, including:
- First-Come, First-Served (FCFS)
- Round-Robin
- Shortest-Job First (SJF)
- Priority Scheduling
Schedulers
Different types of schedulers manage processes:
- Long-Term Scheduler: Determines which programs are admitted for processing.
- Short-Term Scheduler: Selects a process from the ready queue and allocates the CPU.
Synchronization and Deadlocks
Race Conditions and Critical Sections
Concurrent access to shared data can lead to data inconsistency, known as a race condition. Critical sections are code segments that access shared data and require protection.
Semaphores
Semaphores are synchronization tools. Binary semaphores are used for mutual exclusion, while counting semaphores manage resource access.
Deadlocks
Deadlocks occur when processes are blocked indefinitely, waiting for each other. Four conditions must be met for a deadlock to happen:
- Mutual Exclusion
- Hold and Wait
- No Preemption
- Circular Wait
Memory Management
Paging and Virtual Memory
Paging is a memory management scheme that divides physical memory into fixed-size blocks called pages. Virtual memory allows processes to address more memory than physically available.
Demand Paging
Demand paging brings pages into memory only when needed, improving memory efficiency.
Copy-on-Write
Copy-on-Write (COW) allows processes to share memory pages until one modifies them, optimizing memory usage.
File Systems
Virtual File Systems (VFS)
VFS provides a common interface for different file system types, simplifying file system management.
File System Structures
File systems can have various structures, including tree-structured directories.
Interrupts and Signals
Types of Interrupts
Interrupts can be software-generated (synchronous) or hardware-generated (asynchronous).
Signals
Signals are software interrupts used for inter-process communication.
Multi-Processor Systems
CPU Affinity
CPU affinity helps reduce the overhead of process migration in multi-processor systems.
Input/Output (I/O)
Disk Scheduling
Disk scheduling algorithms optimize disk access, minimizing seek time and rotational latency.
Conclusion
This comprehensive overview covers essential operating system concepts, including processes, threads, scheduling, synchronization, memory management, and file systems. Understanding these concepts is crucial for comprehending how modern operating systems function.