Bug #4681

closed

Timeout.timeout doesn't actually time out?

Added by meta (mathew murphy) over 13 years ago. Updated almost 13 years ago.

Status:

Rejected

Assignee:

akr (Akira Tanaka)

Target version:

1.9.3

ruby -v:

1.9.2p180

Backport:

[ruby-core:36153]

Description

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.

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#1 [ruby-core:36162]

Updated by normalperson (Eric Wong) over 13 years ago

mathew murphy meta@pobox.com 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

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#2 [ruby-core:37489]