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The [[*UNIX signalling mechanism*|unix/signal]] is implemented for the GNU Hurd
by means of a separate *[[signal_thread]]* that is part of every user-space
[[process]].  This makes handling of signals a separate thread of control.
[[GNU Mach|microkernel/mach/gnumach]] itself has no idea what a signal is and
`kill` is not a [[system_call]] (as it typically is in a [[UNIX]] system): it's
implemented in [[glibc]].

  * [[SA_SIGINFO, SA_SIGACTION|open_issues/sa_siginfo_sa_sigaction]]

  * Why does `kill` hang sometimes?

        <youpi> kill send the signal to the process
        <youpi> if the process is hung, killing waits
        <youpi> signals should be just asynchronous, but apparently for some
          reason Roland & co wanted some synchronization

    [[!taglink open_issue_glibc]]

  * [[Critical_Section]]s


# Further Reading

  * {{$unix#djb_self-pipe}}.

  * {{$unix#rjk_fork}}.