Re: [Boost-bugs] [Boost C++ Libraries] #2854: Boost assertion fails inconsistently

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #2854: Boost assertion fails inconsistently
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2009-03-16 11:53:43

#2854: Boost assertion fails inconsistently
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  Reporter:  dineshkherajani_at_[hidden]  |       Owner:  johnmaddock
      Type:  Bugs                       |      Status:  closed     
 Milestone:  Boost 1.39.0               |   Component:  regex      
   Version:  Boost 1.35.0               |    Severity:  Problem    
Resolution:  invalid                    |    Keywords:             
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Changes (by johnmaddock):

  * status:  new => closed
  * resolution:  => invalid

Comment:

 Hi Dinesh,

 there is a race condition in your parseURL function: if two threads enter
 the function at the same time and the variable e has not yet been
 initialised then one thread will start initialising the variable, but the
 other thread may then access it before initialisation is complete.

 There are two possible workarounds:

 1) Make the regular expression a static data member of the URL class - it
 will then get initialised at program startup.  This is then thread safe
 provided no threads call URL::parseURL before the start of main().  One
 other downside is that the regex variable will get initialised whether it
 is used or not: that's not a problem in this one case, but may be if you
 have a *lot* of such variables.

 2) Use boost::call_once to call an initialisation function function that
 initialises the regex: this isn't cost free either as call_once has a non-
 zero overhead.

 I'm going to close this issue down for now, but please reopen if you find
 more problems (or this isn't the solution), or if you need the call_once
 method explaining in more detail.

 Regards, John Maddock.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/2854#comment:3>
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