SIGINT not being captured immediately after using system() command

ruby-talk
1

When I ran the ruby code below, pressing ctrl + c would immediately stop
the program

  trap("INT") { exit }
  while line = gets; puts line; end

However, when I use system() command before the gets, pressing ctrl + c
would not take any effect unless I hit "Enter". It seems like it has to
do with system() forking a child process and somehow the parent could no
longer detect SIGINT. How would you change the code so that ctrl + c
would take immediate effect for the code below

  trap("INT") { exit }

  if system("which ruby > /dev/null")
    puts "ruby is installed"
  end

  while line = gets; puts line; end

···

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2

I also tried to debug the problem by using dtruss (i'm on a mac) while
the ruby program is running and tried to see what the differences are
between the two. Problem is, I don't fully understand the output.
Comparing them though, it seems like what enabled the 1st program to
exit immediately on "ctrl + c" during gets is that the
__pthread_canceled system call was executed.

If you guys have more insights into this, let me know:

case 1 (SIGINT with no system before gets) dtruss output:
http://pastie.org/3305367
case 2 (SIGINT with system before gets) dtruss output:
http://pastie.org/3305276

···

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3

Btw, the behavior I described only happens on ruby-1.8.7-p357. When I
switched to ruby-1.9.2-p290, ctrl + c immediately exits the program for
both cases.

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