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#define HELLO printf("hello\n") void doit () { } if (fork()==0) { fork(); HELLO; return; } HELLO; return; int main() { doit (); HELLO; return 0; } a. Assume no call to fork () fails. How many times does the above program print "hello"? b. Does that answer change if == is changed to != in the doit () function? c. Draw a process graph showing the evolution of this program.

#define HELLO printf("hello\n") void doit () { } if (fork()==0) { fork(); HELLO; return; } HELLO; return; int main() { doit (); HELLO; return 0; } a. Assume no call to fork () fails. How many times does the above program print "hello"? b. Does that answer change if == is changed to != in the doit () function? c. Draw a process graph showing the evolution of this program.

Database System Concepts
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
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```c #define HELLO printf("hello\n") void doit() { if (fork() == 0) { fork(); HELLO; return; } HELLO; return; } int main() { doit(); HELLO; return 0; } ``` ### Questions: a. Assume no call to `fork()` fails. How many times does the above program print “hello”? b. Does that answer change if `==` is changed to `!=` in the `doit()` function? c. Draw a process graph showing the evolution of this program. ### Explanation: The program uses the `fork()` system call to create new processes. The `fork()` call returns zero to the child process and the child's process ID to the parent process. The defined macro `HELLO` is used to print "hello" each time it is invoked. The program is a typical case to study process creation and termination in Unix-like systems. To answer the questions, one must analyze the behavior of `fork()` within the execution flow. 1. **Execution Flow:** - The `main` function calls `doit()`. - In `doit()`, the `fork()` creates a child process. - Depending on the return value, either the child or the parent continues executing. - An additional `fork()` occurs in the child process. - Each valid execution of `HELLO` results in printing "hello". 2. **Process Graph:** - Illustrates the parent-child relationship and the sequence of "hello" prints across processes. Understanding the intricacies of process management and output prediction is crucial for mastering system-level programming.
Transcribed Image Text:```c #define HELLO printf("hello\n") void doit() { if (fork() == 0) { fork(); HELLO; return; } HELLO; return; } int main() { doit(); HELLO; return 0; } ``` ### Questions: a. Assume no call to `fork()` fails. How many times does the above program print “hello”? b. Does that answer change if `==` is changed to `!=` in the `doit()` function? c. Draw a process graph showing the evolution of this program. ### Explanation: The program uses the `fork()` system call to create new processes. The `fork()` call returns zero to the child process and the child's process ID to the parent process. The defined macro `HELLO` is used to print "hello" each time it is invoked. The program is a typical case to study process creation and termination in Unix-like systems. To answer the questions, one must analyze the behavior of `fork()` within the execution flow. 1. **Execution Flow:** - The `main` function calls `doit()`. - In `doit()`, the `fork()` creates a child process. - Depending on the return value, either the child or the parent continues executing. - An additional `fork()` occurs in the child process. - Each valid execution of `HELLO` results in printing "hello". 2. **Process Graph:** - Illustrates the parent-child relationship and the sequence of "hello" prints across processes. Understanding the intricacies of process management and output prediction is crucial for mastering system-level programming.
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