Distributed Programming and Processes Overview

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Questions and Answers

What command is used to view existing segments and semaphores in inter-process communication?

shmdt

ipcrm

shmget

ipcs (correct)

In a multi-threaded program, which of the following statements is true regarding threads?

Each thread has its own signal handlers.

Threads have separate memory spaces.

Threads cannot access the same program code.

All threads share global memory. (correct)

What does the `shmctl` function do in shared memory operations?

Creates a new shared memory segment.

Destroys a shared memory segment.

Attaches a shared memory segment.

Controls shared memory segments. (correct)

Which function is used to detach from a shared memory segment in C?

shmdt Signup and view all the answers

What is the primary advantage of using threads over processes in programming?

Threads allow for easier inter-process communication. Signup and view all the answers

What is the main purpose of distributed programming?

To manage processes that communicate over a network. Signup and view all the answers

Which of the following best describes a thread?

A minimal software processor within which a series of instructions can be executed. Signup and view all the answers

What happens when a thread context is saved?

The current execution stops and data needed for future execution is saved. Signup and view all the answers

In multithreaded web clients, how do threads help deal with network latencies?

By allowing multiple threads to fetch files simultaneously, improving response time. Signup and view all the answers

What is a significant benefit of using threads in making multiple request-response calls?

It results in a linear speed-up if calls are made to different servers. Signup and view all the answers

Which statement correctly describes a process?

A process serves as a software processor which can execute multiple threads. Signup and view all the answers

What is necessary for effective distributed programming?

Proficiency in managing local processes. Signup and view all the answers

Why is creating virtual processors in software advantageous?

It allows for rapid scaling and efficient resource management. Signup and view all the answers

What function is used to create a new thread in Pthread programming?

pthread_create Signup and view all the answers

What is the purpose of a detached thread in Pthread programming?

It can run independently of its parent thread. Signup and view all the answers

Which function is used to lock a mutex in Pthread?

pthread_mutex_lock Signup and view all the answers

Before creating a detached thread, what must be set?

Detach state attribute Signup and view all the answers

What are the two synchronization concepts in Pthread programming?

Mutex and condition variables Signup and view all the answers

Which function can be used to detach a thread after it has been created?

pthread_detach Signup and view all the answers

What is the default state for threads created in Pthread programming?

Joinable Signup and view all the answers

What function should be called to initialize a mutex attribute?

pthread_mutex_attr_init Signup and view all the answers

What must be included when linking a program that uses Posix threads in C?

-lpthread Signup and view all the answers

How can Java threads be implemented on different platforms?

They can be mapped to native threads or emulated as green threads. Signup and view all the answers

What function is necessary to initialize a pthread attribute?

pthread_attr_init Signup and view all the answers

When does a pthread stop executing?

When its start routine function returns. Signup and view all the answers

What is required to stop a pthread properly?

It must call pthread_exit. Signup and view all the answers

What must be done to wait for a stopped thread in pthread programming?

Use the pthread_join function. Signup and view all the answers

Which of the following represents the parameters for creating a pthread?

thread, attr, start routine, arg Signup and view all the answers

Which statement about threads in C and Java is true?

Pthreads are standard in Unix systems. Signup and view all the answers

What is a goroutine in Go?

A type of lightweight thread managed by the Go runtime Signup and view all the answers

Which of the following is NOT a benefit of virtualization?

Faster hardware performance Signup and view all the answers

What is the maximum number of times the 'say' function prints 'hello' in the provided goroutine example?

6 Signup and view all the answers

In which layer does virtualization occur according to the architecture of VMs?

At various levels depending on interface offerings Signup and view all the answers

What does the 'time.Sleep' function do in the provided example code?

Delays the execution of the current goroutine for a specified duration Signup and view all the answers

What does virtualization allow for in terms of component management?

Isolation of failing or compromised components Signup and view all the answers

In the given code example, what will be the first printed output?

hello Signup and view all the answers

Which statement about the architecture of VMs is correct?

Privileged instructions are utilized in the hardware layer Signup and view all the answers

What is the primary purpose of a mutex in Pthread synchronization?

To ensure mutual exclusion in accessing shared resources Signup and view all the answers

In Java thread programming, what must be done to define a new thread?

Inherit from the Thread class and override the run() method Signup and view all the answers

What happens to a Java thread when its run() method returns?

It immediately stops executing Signup and view all the answers

What is the function of the synchronized keyword in Java?

To ensure only one thread executes a method at a time Signup and view all the answers

How is a Pthread mutex initialized?

pthread_mutex_init() Signup and view all the answers

Which statement is true regarding the destruction of a mutex in Pthreads?

A mutex must be destroyed before it can be reused Signup and view all the answers

What is the correct way to start a thread in Java after creating an instance of it?

Use the start() method on the thread instance Signup and view all the answers

What is necessary for a thread to perform synchronization with a mutex?

Lock the mutex before accessing shared resources Signup and view all the answers

Study Notes

Overview of Topics

Topics covered in the presentation include processes, creating/deleting Unix processes, inter-process communication, Posix thread programming, Java thread programming, Goroutines in Golang, and virtualization.

Introduction to Distributed Programming

Distributed programming involves processes communicating over a network.
A fundamental requirement is understanding how to handle processes locally.

Processes Explained

Virtual processors are created in software, augmenting physical processors.
A processor provides instructions and automatically executes instruction sequences.
A thread is a minimal software processor handling instructions, with context saving for later continuation.
A process is a software processor within which one or more threads execute, executing instructions in the thread's context.
Threads share the instructions, global memory, open files, and signal handlers within a process.
Each thread has its own ID, stack, program counter, stack pointer, errno, and signal mask.

Threads and Distributed Systems

Multithreaded web clients hide network latency, where separate threads fetch files needed for an incoming HTML page, each doing a blocking HTTP request.
Display of files happens as they are fetched.
Multiple request-response calls to different machines (RPC) also hide network latencies. A variety of simultaneous requests (each one on the thread) speeds up the overall response.

One Process Composition

A process is composed of a process identifier (integer), executing program instructions, memory for program execution, a program counter (current program location), and signal handlers to define action based on received signals.

Processes and Their Creation

Computers perform concurrent program executions, where each program instance is a process.
The same program can run multiple times as parallel processes, for example when multiple users start the same program on a computer.
Processes are created by other processes. A user-initiated command, like running a program, causes the operating system shell process to create the new program's process.

The `fork()` Primitive

fork() is the Unix method used to create a process.
The child process is a duplicate of the parent process (same program, similar state).
The processes differ in their process IDs, which are returned by fork() appropriately, 0 for the child, or the ID of the child for the parent, or -1 if there is an error during the process creation.
The programmer's program code typically checks fork()'s returned value for error conditions.

The `exec()` Primitives

exec() allows a process to switch to another program, destroying the previous process (code/data).
The environment variables and file descriptors are preserved.
The new code is loaded, and is started from the beginning.

Stopping a Process

A process stops when the main() function returns or when exit() is called.
A process stops after receiving a signal, or when signal handlers in the destination indicate that a signal was received.
The SIGINT signal (typically from user keyboard input) stops processes by default.

Signal Handling

Various signals are sent to processes by the system, indicating events, faults, and errors, like SIGSEGV for segmentation faults (unauthorized memory access) or SIGPIPE if an attempt to write to a pipe that has no reader occurs.

Signal Handlers

A signal handler is a subroutine run when a signal is received.

Inter-Process Communications (IPC)

Processes are typically isolated from each other.
However, processes can communicate via signals, pipes (unidirectional communication channels), shared memory (processes can access the same memory area), and semaphores (used for synchronization).
All these mechanisms are for IPC between processes on the same computer, not distributed processes.

Pipes

Pipes are unidirectional communication channels between processes.
Data written to a pipe is read at the other end.
For bidirectional communication, use two separate pipes.
Pipes are commonly used in shell commands.
Pipes connect processes when those processes share a common ancestor process.

Shared Memory

Processes share access to memory via shared memory segments.
Segments must be created & detached when done.
Careful management is critical to avoid race conditions.

Shared Memory (Example)

Example code is provided that shows the usage of shmget, shmat, shmdt, and shmctl for managing shared memory segments.

Posix Thread Programming

Threads (one process with multiple execution pathways, lighter than processes): allow for concurrent execution within a program and share access to the same program instructions, data, open files, and signal handlers.
Each thread has its own thread ID, stack, program counter, and pointer and stack, errno value, and signal mask.
Threads use specific synchronization mechanisms, like mutexes, to control concurrent access to shared resources.

Threads in C and Java

POSIX threads (pthreads) are common in Unix-based systems, and thread-specific libraries must be linked (using the -lpthread option, for example).
Java threads are a native feature in Java's virtual machines; they are platform-independent and can map to operating system threads or be emulated in user space.

Creating & Stopping a Pthread

Creating a Posix thread involves using pthread_create.
Stopping a thread is accomplished using pthread_exit.
Threads need to be waited for using pthread_join to allow control flow to handle termination

Pthread Synchronization (with Mutex)

Mutexes (fundamental synchronization tool) provide mutual exclusion for a shared resource.
Thread safety concerns are handled by explicit locking & unlocking when threads require shared resource access.

Creating Java Threads

Java threads extend the Thread class and overload the run() method to define the actions executed by the thread.
Threads are started by calling the start() method.

Stopping Java Threads

Java threads end when the run() method returns.

Java Thread Synchronization (with Monitors)

Java monitors control access to shared resources.
Monitors implicitly involve mutual exclusion.
Monitors ensure that only one synchronization method for a given object can execute at a time.

Condition Variables

Condition variables allow conditional waiting between threads.

Goroutines in Golang

Goroutines are lightweight concurrency units provided by Go, enabling parallel activities within a program.

Goroutines vs Threads

Goroutines are managed by the Go runtime, while threads are managed by the operating system.
Goroutines have lower resources usage than threads due to their implementation by the language's go runtime (vs threads managed by the kernel).
Goroutines provide efficient means for inter-goroutine communication.

Goroutine Example

Example code showing how Goroutines are defined, concurrent processes are managed and execute.

Virtualization

Virtualization provides hardware abstraction, making software portable across different hardware platforms and isolating failing or attacked components.
Virtual Machine (VM) interfaces are abstracted: the running program is isolated to a VM and the associated OS.

VM Architecture

Various levels of virtualization are supported depending on the system components and their interfaces (e.g., library functions, application code, OS, hardware).

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Description

This quiz covers essential concepts in distributed programming, including the creation and management of processes, inter-process communication, and threads in various programming environments like Java and Golang. Explore the differences between processes, threads, and virtual processors, along with their roles in executing instructions. Test your understanding of these foundational programming concepts.