This content originally appeared on DEV Community and was authored by Naman Tamrakar
In this post I will explain how can we clone or create new process of current c program using fork.
Why it is named fork?
When we create child processes and these child processes can also create their own child process It form a tree like structure, So May be that is the reason it is named as fork.
So lets write a simple program to create clone of current process.
#include <stdio.h>
#include <unistd.h> // fork
int main() {
fork();
printf("Hello world -> My PID is %d\n", getpid());
return 0;
}
When we compile this program this program and execute it.
Output
Hello world -> My PID is 18131
Hello world -> My PID is 18132
So let me explain what is happening above.
The execution of program start from the main function and it first get fork() which create a new clone of current process and now both child parent process continues from here and get statement printf so print it on console.
Note: Child process created using
forkexecutes after the fork statement from
Let's take example of one more to get more details about fork.
#include <stdio.h>
#include <unistd.h> // fork
int main() {
printf("Program execution start here.\n");
int r = fork();
printf(
"Hello world -> My PID is %d, I am %s process\n",
getpid(),
r==0 ? "child" : "parent"
);
return 0;
}
Output
Program execution start here.
Hello world -> My PID is 548, I am parent process
Hello world -> My PID is 549, I am child process
Let me explain what is happening above.
Program execution start and get first line printf so print it on console then get fork statement so create new child process at this line. Now in parent program fork return pid of child process but in child process it returns 0 so we check for return value and print based on that only.
Here is one more example
#include <stdio.h>
#include <unistd.h> // fork
int main() {
printf("Program execution start here.\n");
int r;
for (int i=0; i<5; i++) {
if ((r=fork())==0) {
break;
}
}
printf(
"Hello world -> My PID is %d, I am %s process\n",
getpid(),
r==0 ? "child" : "parent"
);
return 0;
}
Output
Program execution start here.
Hello world -> My PID is 635, I am child process
Hello world -> My PID is 636, I am child process
Hello world -> My PID is 637, I am child process
Hello world -> My PID is 638, I am child process
Hello world -> My PID is 634, I am parent process
Hello world -> My PID is 639, I am child process
The output of this program seems weird as parent program output before the last child process. Let me explain what happening in the above code.
In the loop we execute fork and response is stored in predefined variable r. So in the child process It will be zero so loop breaks out in child process and further program executes. But in parent program loop will not break and it will continue to create new child process.
So these child process are being created and executed in parallel by CPU. But the last child process execute after the child process because after creation of last child process loop breaks and printf statement execute in parent process.
But why last process executed after parent?
One reason may be it take some time to load program in memory and schedule it by CPU to execute. But parent program is already ready ready so it execute first.
NOTE: The above reason for execution order may be not accurate. It is just one assumption made by me. So the execution order may vary from machine to machine.
So that's it about fork to clone current process. In the above I may be wrong somewhere. Please write in comment If you find so. Thank you so much for reading it completely.
Summary
-
forkcan be used to clone current process. - Only the program after the fork is clone not the whole program.
-
forkreturns PID of child process created in parent program but returns0in child process created. So one can use their logic based on return value to differentiate between child and parent process.
Please give a thumbs up If you like this post.
This content originally appeared on DEV Community and was authored by Naman Tamrakar
Naman Tamrakar | Sciencx (2022-07-10T13:56:20+00:00) How to create new process of current program in c using fork. Retrieved from https://www.scien.cx/2022/07/10/how-to-create-new-process-of-current-program-in-c-using-fork/
Please log in to upload a file.
There are no updates yet.
Click the Upload button above to add an update.