Determine the fork and execlp functions - linux, Operating System

Assignment Help:

Assignment

  • What I'm covering:
  • General control flow
  • fork()
  • execlp()
  • Parameters
  • Makefiles
  • Additional Questions

General Control Flow/fork()

  • In the Controller:

int main(int argc,char** argv){

.....

for(i = 0;i < 4;i++){

int ret_pid = fork();

if ( ret_pid < 0 ) exit(1); //this means fork() failed

else if ( ret_pid == 0 ) !  //this is the child

else ...  //this is the parent (Controller)

}

return 0;

}

 

execlp()

  • This function call has a lot of gotchas that look very confusing at first glance.
  • The first argument to execlp is the string with the file name that will be executed...and so is the second.
  • Think about your own program being called from the command-line ( > ./a.out arg1 arg2 ). In this case, the value of argv[0] in the program is "a.out".

Same thing applies when using exec, you just have to be explicit about it.

 

More execlp() and parameters

  • The rest of the parameters to execlp are strings containing the rest of the arguments, in our case, the numbers that the calculator will be operating on.
  • These will be passed to Controller as arguments, and from there, they will be passed to Calculator.
  • No matter what, the last argument to execlp MUST be a null-terminator (NULL or (char*) 0).

This is because the argument list must be null-terminated, just like any other string.

 

Makefiles

  • This assignment requires that TWO executables be created: the Controller and the Calculator.
  • Because of how Eclipse generates its makefiles, if you try to do this in a single project, Eclipse will whine. I recommend doing your coding in a normal text editor (gedit, emacs, vi, bluefish, etc.), and writing your own makefile.
  • There are plenty of makefile tutorials online; but this project (and the next one) will not require a particularly complex makefile.

 

Makefile example

  • Here's the general format of a makefile entry:

[target] : [dependency1] ! [dependencyn] [command to execute]

  • In this example, when you call make target, the make program checks if any of the dependencies of target are out of date.
  • If one or more of them is out of date, the command to execute is run.

Related Discussions:- Determine the fork and execlp functions - linux

Define unix device driver, Define UNIX device driver The UNIX device dr...

Define UNIX device driver The UNIX device driver is structured into two halves called top half and bottom half

For what reason would such a scheme be useful, Q. A Burroughs B7000/B6000 ...

Q. A Burroughs B7000/B6000 MCP file is able to be tagged as sensitive data. When such a file is removed its storage area is overwritten by some random bits. For what reason would

What happens when you execute a program in unix, When you run a program on ...

When you run a program on your UNIX system, the system prepares a special environment for that program. This environment owns everything needed for the system to execute the progra

Determine a parser which is a variant of top-down parsing, Determine a pars...

Determine a parser which is a variant of top-down parsing without backtracking Recursive Descend parser is a variant of top-down parsing without backtracking.

Action taken by the operating system when a page fault occur, Q. Under what...

Q. Under what conditions do page faults occur? Explain the actions taken by the operating system when a page fault occurs. Answer: A page fault take places when an access to

Benefits of dynamic linkage of libraries, Q. What are three benefits of dyn...

Q. What are three benefits of dynamic (shared) linkage of libraries compared to static linkage? What are two situations where static linkage is preferable? Answer: The

Operating system, What criteria are important in choosing a file organisati...

What criteria are important in choosing a file organisation?

What are a safe state and an unsafe state, What are a safe state and an uns...

What are a safe state and an unsafe state? Answer:  A state is safe if the system can allocate resources to every process in some order and still avoid a deadlock. A system is

Unix, UNIX Shell and History feature. 1.Creating a child process. 2.Creatin...

UNIX Shell and History feature. 1.Creating a child process. 2.Creating a history feature. Its exactly "programming project 1 - Unix Shell and History Feature (p.157-159)" in the Si

What is the purpose of the global catalog, Question: (a) i. Consider A...

Question: (a) i. Consider Active Directory as a database, then for each type and new class of objects, what is created? ii. What is the purpose of the global catalog? ii

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd