Bug #4681: Timeout.timeout doesn't actually time out?

• Status: Rejected
• Assignee: akr (Akira Tanaka)
• Target version: 1.9.3
• ruby -v: 1.9.2p180

[meta (mathew murphy)]

Documentation for Timeout says "A way of performing a potentially long-running operation in a thread, and terminating its execution if it hasn‘t finished by a fixed amount of time."

This doesn't actually seem to be what it does.

Example code:

#!/usr/bin/ruby

encoding: UTF-8

require 'open3'
require 'timeout'

puts "Time out after 2 seconds. Count them..."
result = Timeout.timeout(2) do
stdin, stdout, stderr = Open3.capture3("sleep 30")
output = stdout.read + "\n" + stderr.read
end

On my systems, this doesn't time out after 2 seconds. Instead, it runs for 30 seconds, and then throws an error saying it took longer than 2 seconds.

[normalperson (Eric Wong)]

mathew murphy [e-mail] wrote:

This doesn't actually seem to be what it does.

Example code:

#!/usr/bin/ruby

encoding: UTF-8

require 'open3'
require 'timeout'

puts "Time out after 2 seconds. Count them..."
result = Timeout.timeout(2) do
stdin, stdout, stderr = Open3.capture3("sleep 30")
output = stdout.read + "\n" + stderr.read
end

On my systems, this doesn't time out after 2 seconds. Instead, it runs
for 30 seconds, and then throws an error saying it took longer than 2
seconds.

It's because open3 has an ensure block where it does Thread#join and
that waits forever, so the timeout thread raised to unblock the
main thread, and then it got stuck again inside the ensure block.

diff --git a/lib/open3.rb b/lib/open3.rb
index b65cb19..d335f9f 100644
--- a/lib/open3.rb
+++ b/lib/open3.rb
@@ -207,6 +207,7 @@ module Open3
begin
return yield(*result)
ensure

•    p [ :ensure, __FILE__, __LINE__ ]
  

  parent_io.each{|io| io.close unless io.closed?}
  wait_thr.join
  end
  @@ -702,6 +703,7 @@ module Open3
  begin
  return yield(*result)
  ensure

•    p [ :ensure, __FILE__, __LINE__ ]
  

  parent_io.each{|io| io.close unless io.closed?}
  wait_thrs.each {|t| t.join }
  end

You can work around it by having an extra timeout block (ugly):

puts "Time out after 2 seconds. Count them..."
Timeout.timeout(2) do
result = Timeout.timeout(2) do
stdin, stdout, stderr = Open3.capture3("sleep 30")
output = stdout.read + "\n" + stderr.read
end
end

But IMHO, timeout is a very fragile module and shouldn't be relied on.

--
Eric Wong

[naruse (Yui NARUSE)]

• Status changed from Open to Assigned
• Assignee set to akr (Akira Tanaka)

[nahi (Hiroshi Nakamura)]

• Target version set to 1.9.3

[kosaki (Motohiro KOSAKI)]

• Status changed from Assigned to Rejected

I think Eric described the reason and workaround at commetn#1. IOW, it's spec unfortunately.

[meta (mathew murphy)]

Just noting for the benefit of anyone else passing by that I posted a way to do popen3 with timeout at
https://gist.github.com/1032297