Operating Systems Process Termination

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Questions and Answers

What is the main characteristic of an unbounded buffer in the producer-consumer problem?

It is always implemented using shared memory.

It allows any number of items to be stored. (correct)

It leads to performance bottlenecks.

It has a fixed size.

In the context of the bounded-buffer solution, which of the following variables represents the head of the buffer?

out (correct)

head

tail

Which of the following best describes how buffer management is implemented in the bounded-buffer solution?

Using random access to items.

Using a LIFO approach.

Using a FIFO or Queue approach. (correct)

Using a direct access mechanism.

What does the variable BUF_SZ signify in the bounded-buffer shared-memory solution?

The maximum buffer length. Signup and view all the answers

Which of the following is NOT a method mentioned for solving the producer-consumer problem?

Implementing a mutex lock. Signup and view all the answers

What is a key benefit of having each browser tab run in a separate renderer process?

It minimizes the effect of security exploits across tabs. Signup and view all the answers

What is one of the main reasons for using cooperating processes?

To enable information sharing between processes. Signup and view all the answers

Which model of interprocess communication allows multiple processes to access a common memory space?

Shared memory. Signup and view all the answers

In the producer-consumer problem, what role does the consumer process typically play?

It receives and utilizes data generated by the producer. Signup and view all the answers

What facilitates the creation of shared memory areas for interprocess communication?

The operating system kernel facilitates the creation. Signup and view all the answers

What is a significant challenge when using shared memory for interprocess communication?

Providing mechanisms for synchronization among processes. Signup and view all the answers

What type of communication model may involve Unix pipes or TCP/IP sockets?

Message passing. Signup and view all the answers

Which of the following is NOT a reason for processes to cooperate?

Increased data redundancy. Signup and view all the answers

What is the primary role of the exit() system call in process termination?

It signals the operating system to delete the process and return status data to the parent. Signup and view all the answers

What happens to a terminated child process in a system that does not allow orphan processes?

The operating system automatically terminates all descendants of the child. Signup and view all the answers

What is the effect of calling the abort() system call on a child process?

It immediately terminates the child process without cleanup. Signup and view all the answers

What is typically returned by the wait() system call?

Status information and the PID of the terminated process. Signup and view all the answers

In which situation does a terminated process become a zombie?

When the parent process fails to invoke wait() after the child has terminated. Signup and view all the answers

What happens if a parent process terminates while its child is still running in Linux?

The child becomes an orphan and its new parent is the init process. Signup and view all the answers

Which of the following is a characteristic of the process architecture used by modern web browsers like Mozilla Firefox and Google Chrome?

They use separate processes for rendering web pages and managing the user interface. Signup and view all the answers

What is the purpose of the init process in relation to orphan processes?

To periodically invoke wait() to release resources from orphan zombie processes. Signup and view all the answers

What is the purpose of the 'in' and 'out' variables in a bounded buffer implementation?

To represent the head and tail positions of the buffer Signup and view all the answers

Why can only BUFFER_SIZE - 1 elements be used in this bounded buffer solution?

To ensure there's always an empty spot for the producer Signup and view all the answers

What happens if both the producer and consumer access the same buffer location at the same time?

Data corruption can occur due to concurrent access Signup and view all the answers

In the given pseudocode for the producer, what condition is checked to ensure space is available in the buffer?

if (((in + 1) % BUF_SZ) != out) Signup and view all the answers

What type of loop is used in the consumer to wait for an item to be available for consumption?

Busy-wait loop Signup and view all the answers

What condition signifies that the buffer is empty in the consumer's pseudocode?

in == out Signup and view all the answers

What is the primary function of the variable 'next_produced' in the producer pseudocode?

To temporarily hold the item being produced Signup and view all the answers

Which operation needs to occur after the producer writes an item into the buffer?

Increment the 'in' index Signup and view all the answers

Study Notes

Process Termination

Process termination involves the process executing its last statement and then requesting deletion from the operating system using the exit() system call.
This results in status data being returned from the child to the parent (via the parent calling wait()), process resources being deallocated by the operating system, and, in Linux, the exit function taking one parameter indicating an error if nonzero (implicitly called when the main routine returns).
Parents can terminate child processes using the abort() system call (or TerminateProcess() on Windows) due to various reasons:
- The child exceeding allocated resources.
- The task assigned to the child becoming unnecessary.
- The parent exiting, and the operating system not allowing the child to continue.

Process Termination Cascades

Some operating systems do not allow a child process to continue if its parent terminates, leading to cascading termination.
In such cases, if a process terminates, all its children, grandchildren, and so on get terminated.
The operating system initiates this termination. This is not the behavior in Linux.

Parent Process Waiting

Parent processes can wait for the termination of a child process using the wait() system call.
This call returns status information and the process ID (PID) of the terminated process.
When a process exits, all resources are deallocated except for its entry in the process table (containing the exit status).
The process table entry is released only after the parent invokes wait() to read the exit status; until then, the terminated child process is called a zombie.
If a parent process terminates before the child (without invoking wait()), the child process becomes an orphan (if allowed by the OS, such as in Linux).
The init process (PID 1) becomes the new parent for orphaned processes and periodically invokes wait() to release orphan zombie processes.

Multiprocess Architecture - Chrome Browser

Many web browsers used to run as single processes, but some still do.
If one website causes issues, the entire browser can hang or crash.
Mozilla Firefox and Google Chrome use a multi-process architecture with three types of communicating processes:
- A browser process manages the user interface as well as disk and network I/O.
- One or more renderer processes render web pages, handling HTML, JavaScript, and other content. A new renderer is created for each tab/website opened.
- One or more plug-in processes for each type of plug-in.

Inter-process Communication (IPC)

Processes within a system can be independent or cooperating.
Cooperating processes can influence or be influenced by other processes, including sharing data.
Reasons for cooperating processes:
- Information sharing (e.g., shared files like databases).
- Computation speedup (if the system has multiple CPU cores).
- Modularity (dividing a program into tasks, feeding or using services of other tasks).
- Convenience (e.g., a user editing while a spell check runs).
Cooperating processes require inter-process communication (IPC).
Two primary IPC models:
- Shared memory.
- Message passing.

Communication Models

Shared memory involves a shared area of memory accessed by processes that wish to communicate.
The OS kernel facilitates the creation of this shared area as each process normally has a separate address space.
After the OS creates the shared memory, the processes themselves administer the communication mechanism, not the OS.
Message passing involves processes exchanging messages, where each message contains information sent from one process to another.
The OS handles the message exchange details, including buffering messages and delivering them to the correct recipient.

The Producer-Consumer Problem

The producer-consumer problem is a common model for cooperating processes.
A producer process creates information that is consumed by a consumer process.
Examples:
- Multiple subtasks composing a broader function, like a compiler producing an object file and a linker consuming object files to create an executable.
- A client generating window commands (e.g., drawing a rectangle) and an X11 display server consuming them.
- An X11 display server generating mouse/keyboard data and a client process receiving mouse clicks or keyboard keys.
X11 servers generally communicate using message passing (via Unix pipes or TCP/IP sockets).

Shared Memory Systems

Processes share an area of memory for communication facilitated by the OS kernel.
Processes manage the communication mechanism after shared memory creation.
Synchronization mechanisms are required to coordinate processes' actions when accessing shared memory.
The OS kernel typically provides synchronization functions for this purpose.

Solving the Producer-Consumer Problem

The producer-consumer problem can be solved using shared memory or message passing.
Two buffer types are used:
- Unbounded buffer: There is no practical limit on the buffer size.
- Bounded buffer: The buffer has a fixed size.

Bounded-Buffer - Shared-Memory Solution

Shared data:
- A fixed size buffer (BUF_SZ).
- A data structure (item) to represent items in the buffer.
- Two integer pointers, in (tail) and out (head), to manage the buffer.
The buffer is administered as a FIFO (First-In, First-Out) queue.

Bounded-Buffer - Shared-Memory Solution - Code Example

Producer pseudocode:
- Repeat indefinitely:
  - Wait until there is space in the buffer (in != out).
  - Produce a new item (next_produced).
  - Add the produced item to the buffer at position in.
  - Increment in modulo BUF_SZ to wrap around the buffer.
Consumer pseudocode:
- Repeat indefinitely:
  - Wait until there is an item in the buffer (in != out).
  - Remove the item at position out from the buffer (next_consumed).
  - Increment out modulo BUF_SZ to wrap around the buffer.

Bounded-Buffer - Shared-Memory Solution - Issues

The provided code uses busy waiting, which can waste CPU resources.
Only BUF_SZ - 1 elements can be used because the consumer waits until the producer has written an item, using the last element of the buffer as a flag.
The producer and consumer can't access the same item simultaneously. This creates problems when accessing shared variables or counters concurrently.

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Description

This quiz covers the concept of process termination in operating systems, focusing on how processes end their execution and the mechanisms involved. It includes details about system calls like exit() and abort(), along with the implications of parent-child relationships in process management.