Operating Systems: Process Management

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Questions and Answers

Which state indicates that a process is currently executing on the CPU?

SLEEPING

RUNNING (correct)

RUNNABLE

ZOMBIE

What happens when a process calls fork() according to the provided information?

It creates a new process with shared address space.

It creates a new process with its own copy of the address space. (correct)

It changes the state of the parent process to SLEEPING.

It terminates the parent process.

What does the term 'ZOMBIE' refer to in the context of process states?

A process that is waiting for a resource to become available.

A process that has finished execution but its parent has not acknowledged it. (correct)

A process that is currently being executed.

A newly created process that has not yet run.

In the xv6 proc structure, which of the following is true about the 'chan' variable?

It holds a channel to sleep on if non-zero. Signup and view all the answers

Which field in the proc structure uniquely identifies a process?

pid Signup and view all the answers

What is the purpose of the fork() function in this program?

To duplicate the current process. Signup and view all the answers

What will the `if (rc < 0)` condition check for?

If the fork() function failed to create a new process. Signup and view all the answers

What output is generated when the child process is successfully created?

hello, I am child (pid:<child_pid>) Signup and view all the answers

What happens after the fork() call if it's successful?

Both the parent and child processes continue execution from the next line. Signup and view all the answers

What is the significance of the wait() system call mentioned?

It causes the parent process to wait until the child process has completed. Signup and view all the answers

What is the definition of a process?

A running program. Signup and view all the answers

What effect does time sharing have on performance?

It may reduce performance due to shared CPU resources. Signup and view all the answers

Which of the following is NOT a component of the machine state in a process?

Network latency. Signup and view all the answers

What function does the status API serve in process management?

Gaining status information about a process. Signup and view all the answers

What happens to a program's heap during process creation?

The heap is created for dynamically allocated data. Signup and view all the answers

Which instruction is executed to halt a runaway process?

Destroy. Signup and view all the answers

What method is used to request memory in a running program?

malloc(). Signup and view all the answers

Which of the following best describes the role of registers in a process?

Registers hold short, temporary data that is crucial during execution. Signup and view all the answers

What happens to a process when it initiates an I/O request to a disk?

It becomes blocked and can no longer use the processor. Signup and view all the answers

Which of the following is maintained in the PCB (Process Control Block)?

Information about each process. Signup and view all the answers

During what process state transition does a process become descheduled?

When it initiates an I/O request. Signup and view all the answers

What structure is specifically used to save and restore a process's register context in the xv6 kernel?

Context Structure Signup and view all the answers

Which of the following describes the 'Blocked' state of a process?

The process cannot proceed until its I/O operation completes. Signup and view all the answers

Which registers are included in the context structure of the xv6 kernel’s Proc Structure?

ebp and esp Signup and view all the answers

What data structure is used to track processes that are ready to run in the operating system?

Process List Signup and view all the answers

What occurs in the 'Ready' state of a process?

The process is prepared to take CPU resources when available. Signup and view all the answers

What does the second process created by the fork() call print?

hello, I am child Signup and view all the answers

What is the return value of fork() when it fails?

A negative number Signup and view all the answers

What function is used to replace the current process image with a new process image?

exec() Signup and view all the answers

What happens if the execvp() call is successful?

The process is replaced and does not return to the original code Signup and view all the answers

What does wait(NULL) do in the parent process?

It waits for the child process to terminate Signup and view all the answers

What is the purpose of the strdup() function in the child process of p3.c?

To duplicate a string for arguments Signup and view all the answers

What is printed by the parent process after the child process executes in p3.c?

hello, I am parent of <child PID> Signup and view all the answers

Which of the following is a correct statement to indicate a successful fork?

The return value is greater than zero Signup and view all the answers

In the context of the exec() system call, what is meant by 'myargs' in p3.c?

It stores arguments for the executed command Signup and view all the answers

What condition is checked to determine a failed fork in the program?

if (rc < 0) Signup and view all the answers

Study Notes

Process Definition

A process is a running program.

The OS can create the illusion that many virtual CPUs exist to allow multiple processes to run.
This is achieved by running one process, stopping it, and then running another in a cycle.
This can impact performance as each program runs slower due to shared CPU resources.

Process API

Create: Creates a new process to run a program (commands in the shell or double-clicking an executable).
Destroy: Terminates a runaway process.
Wait: Pauses execution until another process stops running.
Miscellaneous Control: Offers methods to suspend a process and later resume it.
Status: Provides information about the status of a running process.

Process Creation

Loading the program's code and static data into memory, filling the process' address space.
Initially, programs reside on disk in executable format.
When a process requests dynamic data allocation, the OS allocates memory from the program's heap (using malloc()).
Disk I/O requests cause a process to be blocked until the request completes, allowing the CPU to serve other processes.

Process State Transitions

Processes transition between the following states: Running, Ready, Blocked, Descheduled, and Scheduled.
A process transitions to the Ready state when it is ready to use the CPU but not currently using it.
Blocked state is entered when I/O requests are initiated.
Running, when the process is currently executing using the CPU.
Descheduled when a process is taken off the CPU by the OS.
Scheduled when a process is put back onto the CPU by the OS.

Data Structures

The OS uses key data structures to track information about each process.
Process List: Holds information about ready, running, blocked, and other processes.
Register Context: A structure containing the state of each process' registers (program counter, stack pointer, and frame pointer).

PCB

A process control block is a C structure storing every process' information.

Kernel Proc Structure (xv6)

context: Contains the registers (EIP, ESP, EBX, ECX, EDX, ESI, EDI, EBP) that xv6 saves and restores to stop and restart processes.
proc_state: Enum defining the different states a process can be in (UNUSED, EMBRYO, SLEEPING, RUNNABLE, RUNNING, ZOMBIE).
proc: C structure that holds process-related information like memory, size, kernel stack, state, PID, parent, channel, killed, open files, current directory, context, and the process' trapframe.

The fork() System Call

Creates a new process with a separate copy of the address space, registers, and PC.
Allows both the parent and child process to continue execution from the point of the fork() call.

The wait() System Call

Pauses the caller until the child process has finished executing.
Returns the child's process ID.

The exec() System Call

Replaces the current process' memory space with a new program.
Allows a process to perform a task but change its code to perform a different task.

All of the Above with Redirection

Programs can take input from sources other than the terminal and send output to locations other than the terminal.
This enables more complex interactions with the OS and other programs. It is a fundamental concept in programming.

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Description

This quiz explores the fundamentals of process management in operating systems, including process creation, CPU virtualization, and the Process API. Understand how processes are managed by the OS and the implications for performance and control.