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# Many operating systems allow signals to be sent to running processes.
# Some signals have a defined effect on the process, while others may be
# trapped at the code level and acted upon. For example, your process may
# trap the USR1 signal and use it to toggle debugging, and may use TERM to
# initiate a controlled shutdown.
#
# ```ruby
# pid = fork do
#   Signal.trap("USR1") do
#     $debug = !$debug
#     puts "Debug now: #$debug"
#   end
#   Signal.trap("TERM") do
#     puts "Terminating..."
#     shutdown()
#   end
#   # . . . do some work . . .
# end
#
# Process.detach(pid)
#
# # Controlling program:
# Process.kill("USR1", pid)
# # ...
# Process.kill("USR1", pid)
# # ...
# Process.kill("TERM", pid)
# ```
#
# produces:
#
# ```
#  Debug now: true
#  Debug now: false
# Terminating...
# ```
#
# The list of available signal names and their interpretation is system
# dependent. [Signal](Signal) delivery semantics may
# also vary between systems; in particular signal delivery may not always
# be reliable.
module Signal
  # Returns a list of signal names mapped to the corresponding underlying
  # signal numbers.
  #
  # ```ruby
  # Signal.list   #=> {"EXIT"=>0, "HUP"=>1, "INT"=>2, "QUIT"=>3, "ILL"=>4, "TRAP"=>5, "IOT"=>6, "ABRT"=>6, "FPE"=>8, "KILL"=>9, "BUS"=>7, "SEGV"=>11, "SYS"=>31, "PIPE"=>13, "ALRM"=>14, "TERM"=>15, "URG"=>23, "STOP"=>19, "TSTP"=>20, "CONT"=>18, "CHLD"=>17, "CLD"=>17, "TTIN"=>21, "TTOU"=>22, "IO"=>29, "XCPU"=>24, "XFSZ"=>25, "VTALRM"=>26, "PROF"=>27, "WINCH"=>28, "USR1"=>10, "USR2"=>12, "PWR"=>30, "POLL"=>29}
  # ```
  def self.list: () -> ::Hash[String, Integer]

  def self.signame: (Integer arg0) -> String?

  def self.trap: (Integer | String | Symbol signal, ?untyped command) -> (String | Proc)
               | (Integer | String | Symbol signal) { (Integer arg0) -> untyped } -> (String | Proc)
end