forking

This is a discussion on forking within the C Programming forums, part of the General Programming Boards category; Hi I've been trying to fork 10 children by the same parent, however the parent copies itself each time (as ...

  1. #1
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    forking

    Hi

    I've been trying to fork 10 children by the same parent, however the parent copies itself each time (as it should do afterall).. My question is now is there a way to fork n children such that all will have the same parent? and you will keep all the returned children ids in the parent in an array?

    thx

  2. #2
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by Cmaniac View Post
    I've been trying to fork 10 children by the same parent, however the parent copies itself each time (as it should do afterall).. My question is now is there a way to fork n children such that all will have the same parent? and you will keep all the returned children ids in the parent in an array?
    I don't understand the question. How are you doing it currently? If the parent (original process) goes in a loop and fork()'s n times, then there will be n children, all children of the same original process.

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    Deathray Engineer MacGyver's Avatar
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    Quote Originally Posted by Cmaniac View Post
    My question is now is there a way to fork n children such that all will have the same parent?
    Yes.

    Quote Originally Posted by Cmaniac View Post
    and you will keep all the returned children ids in the parent in an array?
    Sure, why not?

  4. #4
    and the hat of wrongness Salem's Avatar
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    Use a for loop

    Code:
    pid_t pids[10];
    for ( i = 0 ; i < 10 ; i++ ) {
      pid[i] = fork();
      if ( pid[i] == 0 ) break;  // now in child, no more fork
    }
    // at this point in the code
    if ( i < 10 ) {
      // in the i'th child
    } else {
      // in the parent
    }
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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    thanks salem, i did something similar to what you answered me... at first i was trying it from 'main' when i then moved it into a function all i started getting was segmentation faults. I started eliminating line by line and testing and noted that:

    Code:
      pid_t pids[10];
    cannot be of that type when inside a function.... Strange really, i don't know why it happens. Anyay i changed it to int and it now seems to be working.. However im not sure if an int covers all the range in process ids.. some1 can confirm this? an in is 32bits no.. i think it does anyway

    Listen another small question as the server i was working on is down and I can't try it myself at the moment and i'm in the design phases and will block for sometime if I don't clear this out....

    a child can kill his siblings considering it knows their process ids right? which i will keep in an array on shared memory...

    Thanks
    Last edited by Cmaniac; 04-14-2007 at 12:36 AM.

  6. #6
    and the hat of wrongness Salem's Avatar
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    > cannot be of that type when inside a function.... Strange really
    Not really, there's bugs in your code.
    Especially since your 'fix' makes no sense at all.

    > However im not sure if an int covers all the range in process ids
    No, a pid_t covers the range of process IDs, that's what it's there for.

    > a child can kill his siblings considering it knows their process ids right?
    Well the pid array will contain the process IDs of all the children created before itself (think about it).
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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    >> However im not sure if an int covers all the range in process ids
    >No, a pid_t covers the range of process IDs, that's what it's there for.

    as for that i meant that an int will cover all process IDs, that is will i be guaranteed that every process id will fit in an int variable?

    as for the other about forking, i just found out that its a better design choice for what i'm trying to achieve to kill the children from the parent, after saving a chunk in shared memory with the child's id wishing to kill his siblings. The parent will then have the pids of all its children and will start killing the children from a for loop, and will only skip the one with its cid saved in the shared memory...

    Thanks

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