# Why doesn't Timeout work with String#=~

**URL:** <https://www.ruby-forum.com/t/why-doesnt-timeout-work-with-string/77682>\
**Category:** Ruby\
**Created:** [November 29, 2006, 6:26pm UTC](https://www.ruby-forum.com/t/why-doesnt-timeout-work-with-string/77682 "2006-11-29T18:26:07Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![robtotheb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/db5fbb/32.png) [@robtotheb](https://www.ruby-forum.com/u/robtotheb)\
**Post date:** [November 29, 2006, 6:26pm UTC](https://www.ruby-forum.com/t/why-doesnt-timeout-work-with-string/77682/1 "2006-11-29T18:26:07Z")

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Sorry for the length, but I hope that will a running test case,  
someone can explain this one. I’m running this on Mac OS X 10.4.8  
and with ruby 1.8.4

Apple’s ruby is still present, but shouldn’t be used  
rab:ruby $ whereis ruby  
/usr/bin/ruby  
rab:ruby $ /usr/bin/ruby -v  
ruby 1.8.2 (2004-12-25) [universal-darwin8.0]

rab:ruby $ which ruby  
/usr/local/bin/ruby  
rab:ruby $ ruby -v  
ruby 1.8.4 (2005-12-24) [i686-darwin8.5.2]  
rab:ruby $ /usr/bin/env ruby -v  
ruby 1.8.4 (2005-12-24) [i686-darwin8.5.2]

rab:ruby $ uname -mrsv  
Darwin 8.8.1 Darwin Kernel Version 8.8.1: Mon Sep 25 19:42:00 PDT  
2006; root:xnu-792.13.8.obj~1/RELEASE\_I386 i386

The rest of the email should be runnable as a test case to show the  
problem. Disable the test\_the\_bad\_regexp or uncomment the sleep  
within it to run without any intervention.

The comments in the test case tell the rest of the story…

-Rob

#!/usr/bin/env ruby -w

# 

# I ran into trouble running a test on the result of a spell-checking

action

# with a combination of a poorly formed regular expression and having

a third

# misspelled word in the test phrase. It was taking a LONG time (not

# completed overnight!) so I thought I’d put a timeout around the

call so even

# a truly gastly expression would be halted after some reasonalbe

amount of

# time.

# 

# However, it appears that the regular expression match with =~

doesn’t get

# interrupted by the timeout. Is this expected? I found a thread about

# timeout and syscalls

# ([http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/](http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/)

1. that

# says that syscalls are interrupted which seems to imply that things

like

# String#=~ ought to timeout also.

# 

# Here’s a “minimal” test that pulls the actual response out (so I

don’t have

# to try and recreate a string that will cause the regexp to churn for a

# long while).

require ‘test/unit’  
require ‘timeout’

class TimeoutRegexpTest \< Test::Unit::TestCase  
include Timeout

def setup  
# Note that this actually has three: 1) prhase =\> phrase  
# 2) twoo =\> two  
# 3) incorrectlly =\> incorrectly  
# so the regexp (which expects only 1 and 2) doesn’t match…  
@phrase = “This prhase has only twoo incorrectlly spelled words.”  
@result = \<\<RESULT  
This prhase

- praise

- prose
\n- prates
\n- Pres
\n- praises
\n- pres
- paras
\n- prays
\n- prams
\n- prats
\n- preses
- proses
\n- Prissie
\n- presser
\n- pressie
- presses
\n- pries
\n- peruse
\n- press
- prance
\n- Pr's
\n- Pris
\n- pros
\n- pariahs
- prices
\n- prides
\n- primes
\n- prizes
- probes
\n- proles
\n- protease
\n- proves
- prudes
\n- prunes
\n- parades
\n- pirates
- prissy
\n- precise
\n- preface
\n- preheats
- premise
\n- profuse
\n- promise
\n- propose
- rehearse
\n- pares
\n- peres
\n- pores
- pyres
\n- Price
\n- Pru's
\n- Pryce
\n- preys
- price
\n- prize
\n- prosy
\n- prows
\n- para's
- preps
\n- prigs
\n- prods
\n- profs
\n- proms
- props
\n- piranhas
\n- purees
\n- Prensa
- Ypres
\n- praise's
\n- pram's
\n- prat's
- Peria's
\n- Prince
\n- prince
\n- pros's
- prig's
\n- Priam's
\n- pariah's
\n- prose's
- Prue's
\n- prey's
\n- prow's
\n- pyre's
- Pren's
\n- Prut's
\n- prep's
\n- prof's
- prom's
\n- piranha's
\n- parade's
\n- Prague's
- Brahe's
\n- pirate's
\n- pride's
\n- prude's
- puree's
\n- Price's
\n- Pryce's
\n- price's
- prize's

 has only twoo
- two
- too
\n- woo
\n- twos
\n- two's

 incorrectlly
- incorrectly
- incorrect
\n- indirectly
\n- uncorrectable
\n- uncorrected
- incorrigibly

 spelled words. RESULT @result.chomp! # This is "bad" because it backtracks so much trying not to be greedy (\*?) @bad\_re = %r{\AThis prhase
(?:- .\*?
\n?)+
 has only twoo
(?:- .\*?
\n?) +
 incorrectlly spelled words.\z}ms # This is "good" because it's fast enough to know there is no match @good\_re = %r{\AThis prhase
(?:- [^\<]\*
\n?)+
 has only twoo
(?:- [^\<]\*
\n?) +
 incorrectlly spelled words.\z}ms end

def test\_a\_good\_regexp  
assert\_nothing\_raised Timeout::Error do  
timeout(2) do  
assert\_nil(@result =~ @good\_re)  
end  
end  
end

def test\_a\_timeout  
assert\_raise Timeout::Error do  
timeout(2) do  
sleep 10  
flunk ‘What about the timeout?’  
end  
end  
end

def test\_the\_bad\_regexp  
delay=5  
print “(timeout is #{delay}: interupt sooner and test fails,\n”  
print " count to #{2\*delay} and then interupt it and the test  
PASSES!?)"  
$stdout.flush

```
 assert_raise Timeout::Error do
   timeout(delay) do
     # uncomment the sleep and see it timeout "properly"
     # sleep 2*delay
     assert_send [@result, :=~, @bad_re], "bad test or bad

```

result?? "  
end  
end  
print "If there’s a dot I pass =\> "; $stdout.flush  
end  
end  
**END**

Rob B. [http://agileconsultingllc.com](http://agileconsultingllc.com)  
removed\_email\_address@domain.invalid

---

<div class="post-metadata">

**Author:** ![robtotheb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/db5fbb/32.png) [@robtotheb](https://www.ruby-forum.com/u/robtotheb)\
**Post date:** [November 30, 2006, 6:40am UTC](https://www.ruby-forum.com/t/why-doesnt-timeout-work-with-string/77682/2 "2006-11-30T06:40:49Z")

</div>

On Nov 29, 2006, at 0924 , Rob B. wrote:

> # 
> 
> # 
> 
> # Here’s a “minimal” test that pulls the actual response out (so I
> 
> don’t have
> 
> # to try and recreate a string that will cause the regexp to churn
> 
> for a
> 
> # long while).

Timeout uses threads and threads can only be switched when evaluating  
ruby.

String#=~ is written in C and can’t be interrupted by ruby’s thread  
scheduler.

–  
Eric H. - removed\_email\_address@domain.invalid - [http://blog.segment7.net](http://blog.segment7.net)

I LIT YOUR GEM ON FIRE!