Unix process api, Operating System

Assignment Help:

Unix process API

The two most important function calls to use when programming with several processes are fork and exec:

 fork() creates a copy of current process. It gives a different return value to each process and works based on Copy On Write;

 exec() replaces a process with an executable.

(The Windows CreateProcess(...), taking ten arguments, is analogous.)

Notice that fork() implies that each process descends from another process. In fact, in Unix everything descends from a single process called init: basically, init forks a process and then "replaces its code" with, say, the code of bash, using exec().

Example of how to use fork:
#include
#include
#include
int parentid = getpid();
char program_name[1024];
gets(program_name); // reads the name of program we want to start
int cid = fork();
if (cid==0) { // i'm the child
execlp(program_name, program_name, 0); // loads the program and runs it
printf("if the above worked, this line will never be reached\n");
}
else { // i'm the parent
sleep (1); // give my child time to start
waitpid(cid, 0, 0); // waits for my child to terminate
print("program %s finished\n", program_name);
}
Is the sleep(1) call necessary to allow the child process to start? The answer is no, it is not at all necessary. In general, if you think you need to sleep in a program, you are probably doing something wrong, and just slowing down your program. The call to waitpid() is a blocking wait, and will ?rst wait to let the child process start (if it hasn't already), then will wait until it ends.


Related Discussions:- Unix process api

What are batch systems, What are batch systems? Batch systems are quite...

What are batch systems? Batch systems are quite appropriate for implementing large jobs that need little interaction. The user can submit jobs and return later for the results.

Thread, advantages and disadvantages of kernal level thread

advantages and disadvantages of kernal level thread

OS is a resource allocator and control program, why we say OS is a resource...

why we say OS is a resource allocator and control program

What is scheduler, What is scheduler? A process migrates among the vari...

What is scheduler? A process migrates among the various scheduling queues throughout its life time. The OS must choose processes from these queues in some fashion. This selecti

What is time-stamping, time-stamping It is a method proposed by Lampor...

time-stamping It is a method proposed by Lamport, used to sequencing events in a distributed machine without the use of clocks. This process is intended to order events consis

Demand paging, Demand paging gives that pages could only be brought into ...

Demand paging gives that pages could only be brought into memory if the running process acts them. This is usually referred to as lazy evaluation as only those pages operated by

Describe the three levels of data abstraction, There are three kinds of D...

There are three kinds of Data Abstraction: Physical level: The minimum level of abstraction defines how data are saved. Logical level: The next bigger level of a

Research proposal, what topic i choose for os research proposal

what topic i choose for os research proposal

Program, i need the job to be done within 3days

i need the job to be done within 3days

Protection, protection in operating system

protection in operating system

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