IT628: Systems Programming - Process Creation

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Questions and Answers

What is the basic unit of execution in an OS?

A process

What are the main categories of system calls?

File system, multi-tasking mechanisms, inter-process communication

What is the purpose of a "fork()" system call?

To create a new process that is a copy of the calling process.

What differentiates a program from a process?

<p>A program is a static file or set of instructions, while a process is the dynamic execution context of a program.</p> Signup and view all the answers

What does a context switch involve?

<p>Saving the state of the current process and restoring the state of another process before passing control (B)</p> Signup and view all the answers

What value does the 'fork()' function return in the child process?

<p>0 (zero) (B)</p> Signup and view all the answers

What happens when a process calls 'fork()'?

<p>The program is copied and loaded in a new memory space, creating a separate process (B)</p> Signup and view all the answers

In the following code snippet, how many "Hello world!" messages will be printed to the console? c int main() { fork(); printf("Hello world!\n"); }

<p>2 (D)</p> Signup and view all the answers

What is the key advantage of using the fork() system call?

<p>Creating multiple processes without having to reload the same program code for each process (D)</p> Signup and view all the answers

The 'fork()' system call guarantees that the child process will always be created before the parent process continues execution.

<p>False (B)</p> Signup and view all the answers

The 'fork()' system call allows for the creation of multiple child processes within a single parent process.

<p>True (A)</p> Signup and view all the answers

What is the purpose of the 'exec()' system call?

<p>To replace the current running process with a new program.</p> Signup and view all the answers

Match the following system calls with their primary function:

<p><code>fork()</code> = Creates a new process that is a copy of the calling process <code>exec()</code> = Replaces the current process with a new program <code>wait()</code> = Suspends the calling process until a child process terminates <code>exit()</code> = Terminates the calling process <code>signal()</code> = Sends a signal to a process <code>kill()</code> = Sends a signal to a process, often used for termination</p> Signup and view all the answers

The 'strcpy()' system call is used to copy data between two processes.

<p>False (B)</p> Signup and view all the answers

The 'pipe()' system call is used to create a pipe between two processes.

<p>True (A)</p> Signup and view all the answers

What is the role of the operating system when multiple processes run concurrently?

<p>The operating system manages the shared resources, schedules the processes, and ensures that they do not interfere with each other.</p> Signup and view all the answers

What is the primary purpose of concurrent programming?

<p>To leverage multiple processors or cores to improve the efficiency and performance of applications by performing tasks in parallel.</p> Signup and view all the answers

All processes running on a single system must have unique process identifiers (PIDs).

<p>True (A)</p> Signup and view all the answers

The 'fork()' system call can create a child process with a different program code from the parent process.

<p>False (B)</p> Signup and view all the answers

When a process is terminated by the system, its PID is always immediately released for reuse by a new process.

<p>False (B)</p> Signup and view all the answers

The 'fork()' system call is the only mechanism for creating a new process.

<p>False (B)</p> Signup and view all the answers

The fork() function creates a copy of the current process' entire memory space.

<p>True (A)</p> Signup and view all the answers

The 'fork()' and 'exec()' system calls are interchangeable and can be used to accomplish the same goal

<p>False (B)</p> Signup and view all the answers

What is the typical return value of a successful fork() call in the parent process?

<p>The process identifier (PID) of the newly created child process</p> Signup and view all the answers

Explain why the 'fork()' system call is essential for concurrent programming.

<p>The 'fork()' system call is essential for concurrent programming because it allows the creation of multiple processes that can execute concurrently, enabling parallel processing of tasks and improving the overall performance and efficiency of applications.</p> Signup and view all the answers

It is advisable to use fork() system call to create many processes within a loop, for performing a repetitive task.

<p>False (B)</p> Signup and view all the answers

How do you determine which process is the parent and which is the child after a 'fork()' call?

<p>The parent process can identify itself via the return value of 'fork()' which will be a non-zero PID. The child process, on the other hand, will receive a return value of 0.</p> Signup and view all the answers

Flashcards

Process

The fundamental unit of execution within an operating system. It represents a running instance of a program. A process is a dynamic entity, encompassing both the program code and its execution state.

Context Switching

The act of switching control from one process to another by saving the state of the current process, loading the state of the new process, and transferring control to the new process.

fork()

A system call in Unix-like systems that creates a new process, a copy of the calling process (the parent process). The newly created process is called the child process.

exec()

A system call used to execute a new program in the context of an existing process.

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Child Process

A process that has been created by another process (called the parent process).

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Parent Process

The process that created a child process.

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Process Identifier (PID)

A unique identifier assigned to each process within the operating system, making it possible to distinguish between different processes.

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Concurrent Execution

When two or more processes execute instructions that are interleaved in time, giving the illusion that they are running simultaneously.

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Fork() return values

The return value of the fork() system call. Parent process gets the Process Identifier of the child, while the child process gets 0.

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Process Instruction Sequence

Instructions that are executed in a specific order within a process.

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Process State

The state of a process includes its program counter, memory space, open files, and other resources. When control is transferred to a new process, its state is loaded to resume execution.

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System Calls

A set of functions provided by the operating system that allow applications to interact with the OS kernel.

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libc Calls

Functions provided by the C standard library, handling tasks like string manipulation, input/output, and other general-purpose operations.

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Inter-Process Communication (IPC)

A mechanism used by processes to communicate with each other or with the kernel.

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Process Synchronization

A mechanism allowing a process to block its execution, waiting for a specific event to occur. This can be used to synchronize access to shared resources between processes.

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System Call Execution

A sequence of instructions executed by a CPU that causes a transition from user mode to kernel mode, allowing the process to request services from the OS.

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Multitasking

The mechanism by which the operating system manages the execution of multiple processes by switching control between them.

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Operating System (OS)

A software component responsible for managing the resources of a computer system, including memory, CPU, and peripherals, and providing services to running applications.

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Program

A software file containing the instructions for a program. This file is static in nature and does not represent an executing program.

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File System System Calls

A set of system calls that allow programs to interact with the file system, such as creating, opening, reading, writing, and closing files.

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Pipes

A mechanism for transferring data between processes, typically used to communicate information or share data.

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SIGCHLD Signal

This signal is sent to a process when a child process terminates.

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Shared Memory

A mechanism enabling communication between processes that are related (i.e., parent and child processes) via a shared memory space.

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Sockets

A mechanism for communication between processes using a network connection, allowing data exchange over a network.

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Multithreading

A technique for implementing concurrency using lightweight threads within a single process. It allows multiple threads to execute parts of a program concurrently.

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Pipe

A type of communication channel where one process can write data to the pipe and another process can read from it.

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Threads System Calls

A collection of system calls in Unix-like systems that are related to thread management and synchronization, including thread creation, thread termination, mutexes, and condition variables.

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Synchronization

A technique for ensuring that only one process can access a shared resource at a time, preventing data corruption and ensuring data integrity.

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exit()

A system call in Unix-like systems that terminates a process, freeing up the resources it occupied.

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wait()

A system call used by a process to wait for the termination of another process, typically a child process.

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Signals

A mechanism enabling a process to receive notifications of certain events, such as the termination of another process, a user pressing a key, or a network connection being established.

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kill()

A system call for sending signals to processes. This allows one process to send a signal to another process, like a notification.

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Study Notes

Course Outline and Process Creation

  • Course name: IT628: Systems Programming
  • Course focus: System Programming, process creation

Course Description

  • Operating systems (OS) provide constructs and primitives to simplify application development.
  • Students will learn to write applications leveraging important OS features.
  • Lessons often present an OS concept followed by associated system calls.

Main Topics

  • Concurrent programming: Processes, signals, pipes, threads, and synchronization.
  • Network programming: Sockets and servers.

System Calls

  • System calls: Requests to the OS to perform actions on behalf of the user program.
  • Examples include: fork() (creating child processes), exec() (executing programs), and various file system calls (e.g., creat, open, read, write, Iseek, close).
  • System calls are distinct from libc calls (e.g., strcpy).

Categories of System Calls

  • File system: Low-level file I/O operations such as creat, open, read, write, Iseek, and close.
  • Multi-tasking mechanisms: Process control, including operations such as fork, wait, exec, exit, signal, and kill.
  • Inter-process communication: Methods such as pipe, dup, and dup2.

Classroom Organization

  • Lectures, exercises, and code demos will make up the classes.
  • Students are encouraged to ask questions.

Classroom Etiquette

  • Punctuality is expected.
  • Talking and cell phone use will not be tolerated.

Reference Books

  • Keith Haviland, Dina Gray, and Ben Salama: "UNIX System Programming" (Addison-Wesley)
  • Randal Bryant and David O'Hallaron: "Computer Systems: A Programmer's Perspective" (Pearson India)
  • Brian Kernighan and Dennis Ritchie: "The C Programming Language, Second Edition" (Prentice Hall India)

Grade Breakdown

  • Exams (70%): Two in-semester exams and a final exam (in-semester exams weighted 20%, final exam weighted 50%).
  • Lab exercises and homework (30%): Weighted 20% for checkoffs and 10% for other homework assignments. -Lab attendance is mandatory.

Processes

  • A process is a basic unit of execution within an OS.
  • A process is a running instance of a program.
  • A program represents a static file (image).
  • A process includes a program and its execution state.
  • Concurrent processes involve interleaved instructions.

Context Switching

  • Context switch: Transferring control from one process to another.
  • OS saves the current process's state and loads the next process's state.
  • From a user perspective, multiple processes appear simultaneous.

fork() System Call

  • fork() creates a new process.
  • The newly created (child) process runs the same program as the original (parent) process with the same CPU registers and open files.

fork() Return Value

  • fork() returns a unique process identifier (pid_t).
    • Child receives 0.
    • Parent receives the child's pid.

Example fork() code and outputs

  • Demonstrates both parent and child process outputs after fork operation.
    • Shows various possible outcomes with different fork() calls.

fork() Practice Problems

  • Several code examples demonstrate how fork() works. -Provides output examples and possible outcomes relevant to the code.

Additional Notes

  • The order of execution is non-deterministic after a fork.
  • Post-fork, parent and child are separate processes but initially identical.
  • OSs separately manage the data and states of parent and child processes.
  • Control flow may diverge following the fork operation.
  • Illustrates how fork() creates multiple processes.

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