Operating Systems Process Management Quiz

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Questions and Answers

What is a process?

An instance of a running program, which is in execution.

A program by itself is a process.

False

What is the typical memory layout of a process divided into?

Text section, data section, stack, and heap.

Which of these states can a process be in? (Select all that apply)

Waiting Signup and view all the answers

What is context switching?

A technique allowing the CPU to switch between multiple processes. Signup and view all the answers

The process is uniquely identified by a process ______.

identifier (pid) Signup and view all the answers

What does multitasking allow in operating systems?

Concurrent execution of multiple processes Signup and view all the answers

What is the role of a process control block (PCB)?

It contains all the necessary information about a process needed by the operating system. Signup and view all the answers

Match the following process states with their descriptions:

New = The process is being created Running = Instructions are being executed Waiting = The process is waiting for an event to occur Ready = The process is waiting to be assigned to a processor Terminated = The process has finished execution Signup and view all the answers

What is the purpose of process scheduling?

To maximize CPU utilization and manage the degree of multiprogramming. Signup and view all the answers

What is the size of a message that the link can accommodate?

Variable Signup and view all the answers

Is a link unidirectional or bi-directional?

Bi-directional Signup and view all the answers

What are the two types of communication links mentioned?

Direct and Indirect Signup and view all the answers

What is required for processes to communicate in indirect communication?

A shared mailbox Signup and view all the answers

In direct communication, a link may be associated with multiple pairs of processes.

False Signup and view all the answers

What are the two operations defined for indirect communication?

receive(A, message) Signup and view all the answers

Which of the following is not a method of buffering mentioned?

Limited capacity Signup and view all the answers

What are the characteristics of blocking in message passing?

Synchronous communication Signup and view all the answers

Non-blocking communication allows the sender to wait until the receiver is ready.

False Signup and view all the answers

What system call creates a new process?

Fork() Signup and view all the answers

In a producer-consumer model, what operation does the producer perform?

Send a message Signup and view all the answers

What does the exec() system call do?

It replaces the current process with a new program. Signup and view all the answers

What does the zero capacity buffer imply?

Sender must wait for receiver Signup and view all the answers

If fork() fails, it returns 0 to the parent process.

False Signup and view all the answers

What is a zombie process?

A process that has terminated but whose parent has not yet called wait(). Signup and view all the answers

What type of communication does IPC - Message Passing facilitate?

Processes communicate without shared variables. Signup and view all the answers

What are the two fundamental models of inter-process communication?

Shared memory Signup and view all the answers

What does the wait() system call do?

Makes the parent process wait for a child to terminate Signup and view all the answers

In the context of process management, what does pid_t represent?

It represents process identifiers. Signup and view all the answers

A process that is executed last and then asks the operating system to delete it uses the ______ system call.

exit() Signup and view all the answers

Which of the following describes ordinary pipes?

Unidirectional communication Signup and view all the answers

Which section of a process's memory layout contains the program code?

Text section Signup and view all the answers

The stack and heap sections of a process's memory layout have fixed sizes during program execution.

False Signup and view all the answers

What causes CPU to wait while another process is executing an I/O operation?

I/O operations are significantly slower than CPU speed. Signup and view all the answers

The ______ section of a process's memory layout contains global variables.

data Signup and view all the answers

Match the following process sections with their descriptions:

Text section = Contains the program code Data section = Holds global variables Stack = Stores temporary data like local variables Heap = Holds dynamically allocated memory during runtime Signup and view all the answers

In a multitasking operating system, what happens while a running process is waiting for an I/O operation?

Another process may execute. Signup and view all the answers

What characteristic of ordinary pipes restricts access to the communicating processes?

They exist only within the process that created them. Signup and view all the answers

Message passing communication can only occur between related processes.

False Signup and view all the answers

What are the two fundamental models of inter-process communication?

Shared memory and message passing Signup and view all the answers

Named pipes can be accessed without a __________ relationship.

parent-child Signup and view all the answers

Match the following pipe types with their characteristics:

Ordinary pipes = Access restricted to the process that created them Named pipes = Can be accessed by unrelated processes Full-duplex pipes = Allow bidirectional communication Half-duplex pipes = Allow one-way communication only Signup and view all the answers

Which of the following issues is relevant when considering pipes in inter-process communication?

Whether the communication is unidirectional or bidirectional. Signup and view all the answers

What is stored in the program counter?

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

A process can perform multiple tasks at the same time without any threads.

False Signup and view all the answers

What structure represents a process in Linux?

task_struct Signup and view all the answers

The degree of multiprogramming refers to the number of processes currently in ______.

memory Signup and view all the answers

Match each component of the process control block with its function:

Program Counter = Holds the location of the next instruction to execute CPU Registers = Stores contents of process-centric registers Memory-management Information = Shows memory allocated to the process I/O Status Information = Lists I/O devices allocated to the process Signup and view all the answers

Which of the following is a benefit of multithreading in modern operating systems?

Ability to run multiple threads in parallel on multicore systems Signup and view all the answers

Each thread within a process has its own program counter.

True Signup and view all the answers

What type of information is included in the accounting information of a process?

CPU and real-time used, clock time elapsed since start, time limits Signup and view all the answers

What does the wait() system call return?

Status data from the child process Signup and view all the answers

A parent process can terminate child processes using the exit() system call.

False Signup and view all the answers

What happens when a process executes its last statement?

It asks the operating system to delete it using the exit() system call. Signup and view all the answers

The function wait() is used to ensure that the child process finishes before the parent process continues execution. The child process's PID is captured in __________.

status Signup and view all the answers

Match the following system calls with their functions:

fork() = Creates a new process wait() = Waits for a child process to finish exit() = Terminates a process abort() = Terminates a child process from the parent Signup and view all the answers

Which reason might cause a parent process to terminate a child process?

The child process is no longer required Signup and view all the answers

All operating systems allow child processes to continue running if their parent terminates.

False Signup and view all the answers

What does a successful fork() return to the child process?

0 Signup and view all the answers

The parent process can ensure that the child process will always finish first by calling __________ before proceeding.

wait() Signup and view all the answers

What happens when a child process terminates?

The operating system deallocates the child's resources Signup and view all the answers

Study Notes

Process Concept

A process is an instance of a running program (a program in execution).
Process execution must progress in a sequential fashion (no parallel execution of instructions within a single process).
Processes require system resources (CPU time, memory, I/O control, file storage space).
A process represents a unit of work for the operating system.

Program vs Process

A program is a passive entity stored on disk (executable file)
A process is an active entity.
A program becomes a process when it is loaded into memory and given a program counter specifying the next instruction to execute and resource allocation.
Execution of a program starts through user interface events (e.g., GUI clicks, command line input).
A single program can have multiple processes, as seen in multi-user scenarios executing the same program.

Process Memory Layout

A process' memory is typically divided into sections:
- Text section (program code)
- Data section (global variables)
- Stack section (temporary data like function parameters, return addresses, local variables)
- Heap section (dynamically allocated memory during runtime)
The text and data sections are fixed in size, while the stack and heap sections can grow and shrink dynamically.

Multitasking

Multitasking allows the concurrent execution of multiple processes, maximizing CPU utilization.
Even if a process needs to perform a slow operation (like I/O), the CPU can switch to another process, reducing idle time.

Process States

Processes move through different states during execution:
- New: Process is being created.
- Running: Instructions are being executed.
- Waiting: The process is waiting for an event to occur.
- Ready: The process is waiting to be assigned to a processor.
- Terminated: The process has finished execution.

Context Switching and PCB

Context switching allows the CPU to switch between multiple processes for execution.
The system saves the state of the old process and loads the saved state of the new process.
The Process Control Block (PCB) stores information about a process, including:
- Process state (new, running, waiting, etc.)
- Program counter (location of the next instruction to execute)
- CPU registers (contents of all process-specific registers)
- CPU scheduling information (priorities, scheduling queue pointers)
- Memory management information (memory allocated to the process)
- Accounting information (CPU and real time used, time limits, etc.)
- I/O status information (list of allocated devices, open files, etc.)

Threads

Unlike single-threaded processes, multithreaded processes allow multiple threads of control (multiple program counters), potentially improving performance on multicore systems.
Multithreaded processes need additional storage in the PCB to manage multiple program counters and thread details.

Process Scheduling

The number of processes in memory at any given time is the degree of multiprogramming.
Operating systems balance the goals of:
- Maximizing CPU utilization: Having a process running at all times.
- Timesharing: Switching processes quickly to allow interactive programs to respond quickly.
CPU-bound processes spend more time in the CPU, while I/O-bound processes spend more time performing I/O operations.
If there are more processes than CPU cores, the process scheduler selects processes for execution, using various scheduling algorithms.

Scheduling Queues

A multiprogrammed system maintains scheduling queues for managing processes:
- Ready queue: Stores processes ready to execute in the CPU.
- Wait queues: Stores processes waiting for I/O operations to complete
Queues are often implemented using linked lists.

Context Switch

When the CPU switches from one process to another, the kernel saves the context (state) of the old process and loads the context of the new process.
The context is represented in the PCB.

Context Switch Overhead

Context switching is an overhead because the system is not doing any useful work during the switching process.
Overhead is influenced by factors like the complexity of the OS and PCB, hardware support, and the availability of multiple register sets.

Operations on Processes

Operating systems provide mechanisms for managing processes:
- Process creation
- Process termination

Process Creation

Parent processes create child processes, forming a tree of processes.
Processes are uniquely identified via process identifiers (pids), often represented as integers.
Parent processes can share resources with their children in various ways:
- Sharing all resources
- Sharing a subset of resources
- No resource sharing
Parent and child processes can execute concurrently or the parent can wait until the child finishes.
Child processes can be created as duplicates of the parent, inheriting the same program and data, or they can be loaded with a new program.
The fork() system call creates a new process, returning the child's PID to the parent and 0 to the child.
The exec() system call replaces the process' memory space with a new program.
The wait() system call allows a parent process to wait for the termination of a child process.

Process Termination

Processes can be terminated normally after completing their task or abnormally due to error conditions.
The exit() system call terminates a process.
Processes can also be terminated by the operating system.

Pipes

Pipes allow communication between processes.
- A pipe is a special file that can be used for unidirectional communication, like a one-way street for data flow.
- Data is written to one end of the pipe and read from the other end.
Pipes can be used for:
- Inter-process communication between related processes
- Passing output from one program to another
- Creating simple command chains in shell scripts

Inter-Process Communication (IPC)

IPC mechanisms allow processes to communicate and share data:
- Shared memory: Processes share a common block of memory.
- Message passing: Processes exchange messages (data) through a communication channel.
IPC mechanisms are essential for cooperating processes, distributed systems, and user-level applications.

The wait() system call

wait() returns to the parent process once the child process has finished executing.
It can help ensure that the output of a program is deterministic.

Process Termination

A process can terminate by executing its last statement and then calling the exit() system call.
exit() returns status data from the child to the parent using wait().
The parent process can terminate a child process using the abort() system call.
Reasons for terminating a child process include:
- The task assigned to the child is no longer needed.
- The child has exceeded its allocated resources.
- The parent is exiting, and the operating system prohibits a child process from continuing after its parent terminates.

Cascading Termination

Some operating systems do not allow a child process to exist if its parent has terminated.
When a process terminates, all its children must also terminate, a phenomenon known as cascading termination.
This includes all children, grandchildren, and so on.
Cascading termination is initiated by the operating system when a parent process terminates.
The wait() system call allows a parent process to avoid cascading termination by waiting for the termination of a child process.
wait() returns status information and the process ID of the terminated child process to the parent.
It can be called without any arguments, such as wait(NULL).

Zombie and Orphan Processes

When a process terminates, its resources are deallocated, but its entry in the process table remains until the parent process calls wait().
This is because the process table contains the process's exit status.
A process that has terminated but whose parent has not yet called wait() is known as a zombie process.
Once the parent calls wait(), the process identifier of the zombie process and its entry in the process table are released.
An orphan process is a child process that continues running after its parent process has terminated.
This occurs if the parent process fails to call wait() before terminating.

The exec() system call

This system call is used when a program needs to run a different program than the one that called it.
exec() takes the executable file name and a list of arguments terminated by a NULL pointer.
exec() loads the code and static data from the specified executable file and overwrites the current code segment in the address space.
It re-initializes the heap, stack, and other parts of the program's memory space.
Then, the operating system runs the new program.
Control does not return to where exec() was called.
exec() does not create a new process; instead, it transforms the currently running program.

Inter-process Communication (IPC)

Processes within a system can be independent or cooperating.
Cooperating processes can affect or be affected by other processes, including sharing data.
Reasons for cooperating processes include:
- Information sharing.
- Computation speedup.
- Modularity.
- Convenience.

IPC Models

Processes require an IPC mechanism to exchange data and information.
The two fundamental models of IPC are:
- Shared memory: Processes share a region of memory and exchange information by reading and writing data to it.
- Message passing: Processes communicate by exchanging messages.

Pipes

Pipes act as conduits allowing two processes to communicate.
They can be either unidirectional or bidirectional, half-duplex or full-duplex.
There are two types of pipes:
- Ordinary pipes: Cannot be accessed from outside the process that created them. Typically used by parent processes to communicate with their children.
- Named pipes: Can be accessed without a parent-child relationship.

Ordinary Pipes

Ordinary pipes work in a producer-consumer style.
The producer writes to one end of the pipe (the write-end), and the consumer reads from the other end (the read-end).
Therefore, they are unidirectional.
They require a parent-child relationship between the communicating processes.

The pipe() system call

The pipe() system call creates shared memory for communication between two processes.
It must be created before fork() is called.
The parent and child processes can perform single or multiple read and write operations on the shared memory.
The write() function writes to the write port of the pipe.
The read() function reads from the read port of the pipe.

Creating a Pipe

The pipe() function is used to create a pipe.
It takes an array of file descriptors as an argument.
It returns 0 if successful and -1 on error.
The file descriptors in the array are opened for reading and writing, respectively.

Combination of fork() and pipe()

When fork() is called after pipe(), the file descriptors of the pipe are copied to the child process.
The parent and child processes share the same pipe, so they can read and write to each other through it.

C program - use of pipe()

The program demonstrates how to create a pipe, fork a child process, and communicate between them using the pipe.
The parent process writes a message to the pipe, and the child process reads the message from the pipe.

Open Questions

What happens if you invoke fork() multiple times?
How many processes are created, and how can you identify them?
If there are multiple pipes created, how can you handle them for each pair of communicating processes?

IPC - Message Passing

Processes communicate without resorting to shared variables.
IPC facilities provide two operations:
- send(message)
- receive(message)
The size of the messages can be fixed or variable.

Message Passing (cont.)

If two processes, P and Q, want to communicate, they need to:
- Establish a communication link.
- Exchange messages through send and receive operations.
Implementation issues include:
- How are links established?
- Can a link be associated with more than two processes?
- How many links can there be between every pair of communicating processes?
- What is the capacity of a link?
- Is the size of messages that the link can accommodate fixed or variable?
- Is a link unidirectional or bidirectional?

Implementation of Communication Link

The link can have a physical or logical implementation:
- Physical:
  - Shared memory.
  - Hardware bus.
  - Network.
- Logical:
  - Direct or indirect.
  - Synchronous or asynchronous.
  - Automatic or explicit buffering.

Direct Communication

Processes must name one another explicitly.
The primitives are:
- send(P, message): sends a message to process P.
- receive(Q, message): receives a message from process Q.
Properties of direct communication links include:
- Links are established automatically.
- A link is associated with exactly one pair of communicating processes.
- Between each pair, there exists exactly one link.
- The link is usually bidirectional but may be unidirectional.

Indirect Communication

Messages are directed and received through mailboxes (also referred to as ports).
Each mailbox has a unique ID.
Processes can communicate only if they share a mailbox.
Properties of communication links include:
- A link is established only if the associated processes share a common mailbox.
- A link may be associated with many processes.
- Each pair of processes may share several communication links.
- Links may be unidirectional or bidirectional.

Indirect Communication (cont.)

Operations:
- Create a new mailbox (port).
- Send and receive messages through the mailbox.
- Delete a mailbox.
Primitive operations are:
- send(A, message): sends a message to the mailbox with ID A.
- receive(A, message): receives a message from the mailbox with ID A.

Multiple processes can share a mailbox, but the system needs to determine which process receives a message.
To resolve this, the system can:
- Allow a link to be associated with at most two processes.
- Allow only one process at a time to execute a receive operation.
- Allow the system to select the receiver arbitrarily and notify the sender of who the receiver was.

Message Passing Types

Message passing can be blocking or non-blocking.
Blocking is considered synchronous.
- Blocking Send: The sender is blocked until the message is received.
- Blocking Receive: The receiver is blocked until a message is available.
Non-blocking is considered asynchronous.
- Non-blocking Send: The sender sends the message and continues.
- Non-blocking Receive: The receiver receives either:
  - A valid message.
  - A null message.

Producer-Consumer Using Message Passing

Producer: Creates messages and sends them.

Code:

message next_produced;
while (true) {
  // Produce message: next_produced
  send(next_produced);
}

Consumer: Receives messages and consumes them.

Code:

message next_consumed;
while (true) {
  receive(next_consumed)
  //  Consume message: next_consumed
}

Producer and Consumer communicate through a shared message buffer

Buffering

A queue of messages is attached to the link between the producer and consumer.
Buffers can be implemented in three ways:
- Zero capacity: No messages are queued. The sender must wait for the receiver (rendezvous).
- Bounded capacity: A finite length of n messages. The sender must wait if the link is full.
- Unbounded capacity: An infinite length. The sender never waits.

Process Execution

Programs execute by starting as processes
A program can have multiple processes
Multiple users can execute the same program
Processes have memory layout with several sections
Text section contains program code
Data section contains global variables
Stack section contains temporary data and function parameters
Heap section contains dynamically allocated memory during runtime

Memory Layout

Text and data sections have fixed size
Stack and heap sections can grow and shrink dynamically during program execution
Processes are managed in memory by the operating system

Multitasking

Multitasking allows multiple processes to execute simultaneously
CPU can switch between processes while one is waiting for I/O operations

Process Management

Processes can be represented by specific data structures
Linux uses the task_struct structure to represent processes
task_struct contains process ID, state, time slice, parent process, children processes, file usage, memory management info, and accounting information

Threads

Threads are separate units of execution within a process
Each thread has its own program counter, registers, and stack
Multiple threads can run concurrently on multi-core systems
Threads share the same memory and resources as the process

Process Scheduling

The degree of multiprogramming is the number of processes in memory
Process scheduling determines which process will execute next
Different scheduling algorithms exist to optimize resource usage
The wait() system call allows a parent process to wait for the termination of its child process

Process Termination

Processes can terminate normally by executing the exit() system call
Parent processes can terminate child processes using the abort() system call
The wait() system call returns status information and the PID of a terminated child process

Inter-Process Communication

Processes can communicate using shared memory or message passing
Shared memory allows processes to access and modify data in a shared region
Message passing involves sending messages between processes
Pipes are a communication mechanism between processes

Pipes

Pipes allow two processes to communicate with each other
Ordinary pipes are local to the process that created them
Named pipes can be accessed by multiple processes
Pipes can be used for both unidirectional and bidirectional communication

C Program Example

The C program examples demonstrate pipe creation and communication between parent and child processes
The pipe() function is used to create pipes
The fork() function creates child processes
The write() function writes data to a pipe
The read() function reads data from a pipe
The wait() function pauses the parent process until the child process terminates

Open Questions

Multiple fork() calls create a tree of processes
Each process has a unique PID and a parent process
Multiple pipes can be created and handled using appropriate indexing and communication protocols

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Description

Test your knowledge on processes in operating systems, including memory layout, states, context switching, and communication methods. This quiz covers various aspects of process management and scheduling, providing a comprehensive overview of how processes operate within an OS.