It's easiest to explain in code:
require 'timeout'
puts "this block will properly kill the sleep after a second"
IO.popen("sleep 60") do |io|
begin
Timeout.timeout(1) do
while (line=io.gets) do
output += line
end
end
rescue Timeout::Error => ex
Process.kill 9, io.pid
puts "timed out: this block worked correctly"
end
end
puts "but this one blocks for >1 minute"
begin
pid = 0
Timeout.timeout(1) do
IO.popen("sleep 60") do |io|
pid = io.pid
while (line=io.gets) do
output += line
end
end
end
rescue Timeout::Error => ex
puts "timed out: the exception gets thrown, but much too late"
end
My mental model of the two blocks is identical:
So, what am I missing?
edit: drmaciver suggested on twitter that in the first case, for some reason, the pipe socket goes into non-blocking mode, but in the second it doesn't. I can't think of any reason why this would happen, nor can I figure out how to get the descriptor's flags, but it's at least a plausible answer? Working on that possibility.
puts("but this one...")
between the two blocks for me waits until the firstsleep
is complete, because the first IO#popen block is dutifully in a call towaitpid()
. If you don't want that, then your rescue logic needs to kill the child process.