The UNIX signalling mechanism 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 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

• 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
  

  open issue glibc

• Critical Sections

Further Reading

• D. J. Bernstein's self-pipe trick.

• Richard Kettlewell's suggestions about how fork(2) ought to be.