Operating Systems - Processes Overview

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Questions and Answers

What type of information must be saved when an interrupt occurs?

State information of the CPU (correct)

Information about I/O devices only

Only the program counter

Only the condition-code information

Which of these is included in CPU-scheduling information?

List of open files

Base and limit registers

Daily CPU usage time

Process priority (correct)

What happens to a process that issues an I/O request?

It immediately terminates

It becomes the highest priority process

It is placed in an I/O wait queue (correct)

It is removed from the scheduling queue

What does accounting information for a process typically include?

Amount of CPU and real time used Signup and view all the answers

What is true about a child process in relation to its parent process?

It is a duplicate of the parent process initially Signup and view all the answers

Under which condition might a parent process terminate its child process?

If the child exceeds its allocated resources Signup and view all the answers

What typically happens when the time slice of a process expires?

The process is put back into the ready queue Signup and view all the answers

What is a characteristic of the child process when created?

It inherits the parent's resources Signup and view all the answers

What component contains the executable code of a process?

Text section Signup and view all the answers

Which state indicates that a process is actively executing instructions?

Running Signup and view all the answers

What does the program counter in a process control block indicate?

The address of the next instruction to execute Signup and view all the answers

In which section of a process is dynamic memory allocated during runtime?

Heap section Signup and view all the answers

Which statement about process states is true?

The waiting state indicates the process is paused until a certain event occurs. Signup and view all the answers

Which part of the global data section includes initialized and uninitialized data?

Data section Signup and view all the answers

Which of the following is NOT a state of a process?

Initialized Signup and view all the answers

What is stored in the stack section of a process?

Function parameters and local variables Signup and view all the answers

What happens in a zero capacity queue when a message is sent?

The sender is blocked until the recipient receives the message. Signup and view all the answers

In a bounded capacity queue, what occurs if the queue is full when a new message is sent?

The sender must wait until there is room in the queue. Signup and view all the answers

Which type of capacity queue allows an infinite number of messages?

Unbounded capacity. Signup and view all the answers

What is a necessary feature of the message header in Mach Message Passing?

It must contain metadata such as source and destination ports. Signup and view all the answers

What can happen if a sender attempts to send a message to a full queue?

The sender may temporarily cache a message. Signup and view all the answers

What is the purpose of a section object in Windows for larger messages?

To provide a region of shared memory associated with the channel. Signup and view all the answers

Which of the following statements about pipes is NOT true?

Pipes do not allow any form of communication. Signup and view all the answers

What does it mean for a queue to have bounded capacity?

The queue can hold a finite number of messages. Signup and view all the answers

What is the primary role of the init (or systemd) process in UNIX and Linux systems regarding process termination?

It reaps zombie processes and cleans up after terminated processes. Signup and view all the answers

In a UNIX-like program, how many processes are created by the program if the initial parent process is counted?

Two processes, the parent and one child. Signup and view all the answers

When is it more suitable to use ordinary pipes over named pipes?

When communication between parent and child processes is needed in real-time. Signup and view all the answers

What is a possible consequence of not enforcing 'at most once' or 'exactly once' semantics in RPC?

Duplicate execution of operations leading to inconsistency. Signup and view all the answers

Which method effectively guarantees that a process identifier (pid) is unique for each new process in an operating system?

Assigning pids sequentially from a fixed range. Signup and view all the answers

What is a disadvantage of synchronous communication at the system level?

It can block processes, causing delays in execution. Signup and view all the answers

In which scenario are named pipes more beneficial than ordinary pipes?

For establishing long-term connections between unrelated processes. Signup and view all the answers

Which process state indicates that a child process has completed but has not yet been reaped by its parent?

Zombie Signup and view all the answers

What must be unique among active processes in a system?

Process identifiers (pid) Signup and view all the answers

What does the function allocate map() return upon unsuccessful execution?

-1 Signup and view all the answers

In the context of the Collatz conjecture, what happens to the sequence of numbers generated?

It can be stored in a shared-memory object. Signup and view all the answers

What is the significance of port 17 when connecting to a server?

It provides the quote-of-the-day service. Signup and view all the answers

What is the correct syllable structure of a haiku?

5-7-5 Signup and view all the answers

What should the haiku server do when a client connects to it?

Return a haiku to the client. Signup and view all the answers

How does an echo server operate?

It sends received data back to clients. Signup and view all the answers

What function is used to release a pid that is no longer needed?

release pid(int pid) Signup and view all the answers

Study Notes

Processes

A process is a program in execution and consists of the following sections:
- Text section: Contains the executable code
- Data section: Stores global variables
- Heap section: Dynamically allocated memory during program runtime
- Stack section: Used for temporary data storage during function calls
A process can be in one of several states:
- New: The process is being created
- Running: Instructions are being executed
- Waiting: Waiting for an event (e.g., I/O completion)
- Ready: Waiting to be assigned to a processor
- Terminated: Execution has finished
The Process Control Block (PCB) contains information about a process:
- Process state: New, ready, running, waiting, terminated, etc.
- Program Counter: The address of the next instruction to be executed
- CPU Registers: Store values needed for process execution
  - Accumulators, index registers, stack pointers, general-purpose registers
  - These are saved when an interrupt occurs to allow the process to resume correctly
- CPU Scheduling Information: Priority, scheduling queue pointers, etc.
  - Used for managing when and how a process gets to run on the CPU
- Memory Management Information: Base and limit registers, page tables, segment tables
  - Details on how the process's memory is organized
- Accounting Information: CPU time used, real time used, account numbers
  - Used for tracking resource usage
- I/O Status Information: List of allocated I/O devices, open files, etc.
Threads are lightweight processes that share the same address space and resources.
- Multiple threads within a process can execute concurrently, enhancing performance.

Process Scheduling

Scheduling queues: Processes spend time in different queues:
- Ready queue: Processes waiting to be assigned to a CPU
- I/O wait queue: Processes waiting for I/O to complete
- Wait queue: Processes waiting for an event (e.g., child process termination)
CPU Scheduling algorithms: Determine which ready process is assigned to the CPU next.
A context switch is the process of saving the state of the currently running process and loading the state of a new process, allowing the CPU to switch between running processes.
Context switches involve saving the current process's program counter, CPU registers, and other process state information.

Operations on Processes

Process creation: A new process is created, typically by an existing process (the parent).
- The parent can choose to execute concurrently with the child or wait for the child to terminate.
- The child process can be a copy of the parent or have a completely different program loaded.
Process termination: A process can be terminated for various reasons:
- The process completes its assigned task.
- The parent process terminates.
- The process exceeds resource limits.
- The process is abnormally terminated.
Inter-process communication (IPC): Allows processes to communicate with each other.
- Message passing: Processes exchange messages through shared queues.
- Shared memory: Processes access a shared region of memory to communicate.
- Semaphores: Used for synchronizing access to shared resources, preventing race conditions.
- Pipes: Unidirectional or bidirectional connections between processes.
Buffering: Messages are buffered to handle different sending and receiving rates:
- Zero capacity: The sender blocks until the receiver receives the message.
- Bounded capacity: A finite number of messages can be queued, and the sender blocks if the queue is full.
- Unbounded capacity: The queue has potentially infinite length, and the sender never blocks.

Examples of IPC Systems

POSIX Shared Memory: Provides a standard way to create and access shared memory segments across different processes.
Mach Message Passing: A message-passing system that offers a flexible and powerful IPC mechanism.
- Messages include:
  - A fixed-size message header with metadata (size, source, destination ports)
  - A variable-sized body containing data.
- Sending a message to a full queue can be handled in various ways:
  - Wait indefinitely until there is room in the queue.
  - Wait for a specified time (milliseconds).
  - Return immediately without waiting.
  - Temporarily cache the message, notifying the sender when the queue has space.
Windows: Uses a combination of message queues, shared memory (sections), and direct memory access for IPC.

Pipes

Pipes: Allow processes to communicate unidirectionally or bidirectionally.
- Ordinary pipes: A temporary communication channel between related processes.
- Named pipes: Persistent channels that can be accessed by any process on the system.

Additional Notes

Init (or Systemd) Process: The init process (or systemd) is responsible for starting up and managing system processes on Unix and Linux systems. It also handles process termination, ensuring that orphaned processes are properly terminated.
Zombie Processes: A zombie process is a process that has completed execution but its entry in the process table still exists because the parent process hasn't yet called wait() to reclaim its resources.
RPC (Remote Procedure Call): A mechanism that allows a process on one computer to call a procedure/function on a process running on another computer. Guaranteeing at-least-once, at-most-once, or exactly-once semantics for RPC calls is crucial for reliable communication.
Echo server: A simple server that echoes back any data it receives from a client.

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Description

Explore the intricacies of processes in operating systems with this quiz. Understand the different sections of a process, various process states, and the important role of the Process Control Block (PCB). Test your knowledge on key concepts and terminology in this essential topic.