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POKilling child processes from parent's signal handler hangs
 

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  1. POKilling child processes from parent's signal handler hangs
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    <p>I have a problem in topic of posix processes and I can't get around.</p> <p>I have a process which forks several children (the process tree can be complex, not only one level). It also keeps track of the active childrens' PID. At some point the parent receives a signal (SIGINT, let's say).</p> <p>In the signal handler for SIGINT, it iterates over the list of child processes and sends the same signal to them in order to prevent zombies. Now, the problem is that </p> <ol> <li>if the parent does not waitpid() for the child to be stopped, the signal seems to be never dispatched (zombies keep running)</li> <li>if the parent waits after every kill() sent to a child, it simply hangs there and the child seems to ignore the signal</li> </ol> <p>Parent and children have the same signal handler, as it's installed before forking. Here is a pseudocode.</p> <pre><code>signal_handler( signal ) foreach child in children kill( child, signal ) waitpid( child, status ) // Releasing system resources, etc. clean_up() // Restore signal handlers. set_signal_handlers_to_default() // Send back the expected "I exited after XY signal" to the parent by // executing the default signal handler again. kill( getpid(), signal ) </code></pre> <p>With this implementation the execution stops on the waitpid. If I remove the waitpid, the children keep running.</p> <p>My guess is that unless a signal handler has ended, the signals sent from it are not dispatched to the children. But why aren't they dispatched if I omit wait?</p> <p>Thanks a lot in advance!</p>
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    1. COLooks like the children are stuck in the signal handler. What's the value of `children` in the children? What does `cleanup` do?
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    2. CO`childen` in children is empty if they are leaves (containing their children processes otherwise). Just after forking I empty this array in the child. `cleanup` is viod (empty) for the sake of debugging.
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    3. COOut of curiosity, what is the disposition of SIGCHLD?
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      1. USDuck
 

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