Handling exceptions raised in a Ruby thread

If you want any unhandled exception in any thread to cause the interpreter to exit, you need to set Thread::abort_on_exception= to true. Unhandled exception cause the thread to stop running. If you don’t set this variable to true, exception will only be raised when you call Thread#join or Thread#value for the thread. If set to true it will be raised when it occurs and will propagate to the main thread.

Thread.abort_on_exception=true # add this

def foo(n)
    puts " for #{n}"
    sleep n
    raise "after #{n}"
end

begin
    threads = []
    [15, 5, 20, 3].each do |i|
        threads << Thread.new do
            foo(i)
        end
    end
    threads.each(&:join)

rescue Exception => e

    puts "EXCEPTION: #{e.inspect}"
    puts "MESSAGE: #{e.message}"
end

Output:

 for 5
 for 20
 for 3
 for 15
EXCEPTION: #<RuntimeError: after 3>
MESSAGE: after 3

Note: but if you want any particular thread instance to raise exception this way there are similar abort_on_exception= Thread instance method:

t = Thread.new {
   # do something and raise exception
}
t.abort_on_exception = true