Re: [Boost-users] What's wrong with this simple multithreaded function that uses regex?

Subject: Re: [Boost-users] What's wrong with this simple multithreaded function that uses regex?
From: Daniel Anderson (wonixen_at_[hidden])
Date: 2011-08-01 08:14:52

2011/8/1 Andrew Yancy <andrew732_at_[hidden]>

> The code snippet below is the core of a function mythreadfunc() that is
> run concurrently for several threads using the Win32 MSVC functions
> CreateThread() and WaitForMultipleObjects().  Everything seems to work fine
> except for actually using boost::regex_match().  For example, if that line
> below is changed to if(true), the entire multithreaded function works
> perfectly.  Similarly,  if mythreadfunc() as shown below is run without
> multiple threads, it works perfectly.  But if mythreadfunc() as shown below
> is run with multiple threads, the entire program crashes with return value
> 0xc0000005, which is some kind of memory access violation.
>
> This leads me to believe that boost::regex does not play well with MSVC
> threads, but according to the Boost site, there aren't any bugs related to
> this issue for Boost 1.45.  As far as I can tell I'm using Boost in thread
> safe mode (BOOST_HAS_THREADS is defined).  I'm probably doing something
> really dumb related to MSVC threads or related to the way I configured
> Boost, but I'm not sure what it is!  I could switch to using Boost threads,
> but I would like to minimize the changes to the code.  Thanks very much for
> any help~
>
>
>
> ...
> static const boost::regex expression("^[0-9]+");
> ifstream myfile(x); //x is a different file name for every thread
> string line;
> if(myfile.is_open())
> {
>   while(myfile.good())
>   {
>      getline(myfile, line);
>      if(boost::regex_match(line, expression))
>      {
>         //do stuff
>      }
>   }
>   myfile.close();
> }
> ...
>
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>

You should use _beginthread or _beginthreadex to start C++ thread when using
MSVC.
CreateThread is too low level and does not do the per thread initialization
required. If you read MSDN documentation it explain why CreateThread cannot
be use with C++ program.

Daniel Anderson