execvp和fork无法正常工作

Question

I have the following code:

for (loop=0;loop<2;loop++) 
    {
        child_pid = fork();

        if (child_pid == 0)
        {
            rc = execvp ("/usr/local/some_program", arguments);
        }
    }

I change the arguments passed to /usr/local/some_program based on the value of loop. I want the some_program to parallel-ly execute two instances. But i see that i first execute some_program once and only after it finishes that i get execute the second instance of some_program.

I not able to get them to run parallelly and independently.

Instead of fork, should i use pthreads?

The some_program that i am trying to execute is completely unrelated to the parent process.

Thanks

Answer 1

"I not able to get them to run parallelly and independently." - No. Both process will be executed in parallel. To check that create two programs like this-

#include<stdio.h>
#include<sys/types.h>
#include<unistd.h>
int main()
{
   printf("Pid= %d\n", getpid());
   while(1);
}

Compile those 2 program's and make two executable files. Pass these 2 exe file names via command line arguments to main program and run that using system command.But your main program should be live.

for (loop=0;loop<2;loop++) 
{
    child_pid = fork();

    if (child_pid == 0)
    {
       system(argv[loop+1]);
       exit(0); // if you don't use exit your second exe file will be executed twice.
    }
}
while(1);

Now type ps command in terminal and find the TTY name and run the main program. Open a new terminal and type

ps -e  | grep pts/X    // pts/X is main program running terminal name. it may pts/0 or pts/1 ...

Through this you can come to know that the two processes running parallelly or not.