Capturing Ctrl-c in ruby

Question

I was passed a long running legacy ruby program, which has numerous occurrences of

begin
  #dosomething
rescue Exception => e
  #halt the exception\'s pr         


        

Answer 1

The problem is that when a Ruby program ends, it does so by raising SystemExit. When a control-C comes in, it raises Interrupt. Since both SystemExit and Interrupt derive from Exception, your exception handling is stopping the exit or interrupt in its tracks. Here's the fix:

Wherever you can, change

rescue Exception => e
  # ...
end

to

rescue StandardError => e
  # ...
end

for those you can't change to StandardError, re-raise the exception:

rescue Exception => e
  # ...
  raise
end

or, at the very least, re-raise SystemExit and Interrupt

rescue SystemExit, Interrupt
  raise
rescue Exception => e
  #...
end

Any custom exceptions you have made should derive from StandardError, not Exception.

Answer 2

If you can't wrap your whole application in a begin ... rescue block (e.g., Thor) you can just trap SIGINT:

trap "SIGINT" do
  puts "Exiting"
  exit 130
end

130 is a standard exit code.

Answer 3

If you can wrap your whole program you can do something like the following:

 trap("SIGINT") { throw :ctrl_c }

 catch :ctrl_c do
 begin
    sleep(10)
 rescue Exception
    puts "Not printed"
 end
 end

This basically has CtrlC use catch/throw instead of exception handling, so unless the existing code already has a catch :ctrl_c in it, it should be fine.

Alternatively you can do a trap("SIGINT") { exit! }. exit! exits immediately, it does not raise an exception so the code can't accidentally catch it.

Answer 4

Handling Ctrl-C cleanly in Ruby the ZeroMQ way:

#!/usr/bin/env ruby

# Shows how to handle Ctrl-C
require 'ffi-rzmq'

context = ZMQ::Context.new(1)
socket = context.socket(ZMQ::REP)
socket.bind("tcp://*:5558")

trap("INT") { puts "Shutting down."; socket.close; context.terminate; exit}

puts "Starting up"

while true do
  message = socket.recv_string
  puts "Message: #{message.inspect}"
  socket.send_string("Message received")
end

Source

Answer 5

I am using ensure to great effect! This is for things you want to have happen when your stuff ends no matter why it ends.