Fork()

This is a discussion on Fork() within the C Programming forums, part of the General Programming Boards category; Hi, I am currently having issue with a fork command I am issuing, I am attempting to use fork to ...

  1. #1
    Registered User
    Join Date
    Mar 2005
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    24

    Fork()

    Hi,

    I am currently having issue with a fork command I am issuing, I am attempting to use fork to create x number of identical processes however it is creating the required amount and then the child appears to enter into the same fork and create another x amount of forks, is there a trick to avoid this? I am using a for loop to increment until I hit the x amount of forks required.

    I am not looking for code but just some sort of logical thinking around this problem so I can try and get over this hurdle myself.

    Thanks

  2. #2
    Registered User
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    Oct 2006
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    Canada
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    1,243
    Its hard to understand what your doing without seeing the code. Its been a little while since Ive used "fork", etc, but if your doing something like this
    Code:
    int i;
    for ( i=0; i < MAX; i++ )
    {
       fork();
       childFunction(); // this should never return to here
    }
    you should do
    Code:
    int i;
    for ( i=0; i < MAX; i++ )
    {
       if ( fork() == 0 ) // only the child should call the childFunction
       {   
          childFunction(); // this should never return to here
       }
    }
    Also, the key is that "childFunction()" never returns to the calling function. If you have something like
    Code:
    int childFunction() // whatever return type
    {
      // do something
      return 5; // return something
    }
    this child process will return to the calling process, and continue its own "version" of the for loop, the child itself creating its own children (recursively). This is obviously a bad thing. As mentioned, you have to make sure this child function never returns, i.e.
    Code:
    int childFunction() // whatever return type
    {
      // do something
      // kill this process (using kill and getpid()) or simply use an "exit" call so this process ends (exit(0))
      return 5; // required by language to return something, even though it never will (because process would have ended on previous line)
    }

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