Re: [Boost-users] Threads Don't Take Turns Under Linux (Ubuntu Gutsy Gibbon)

From: Mike Marchywka (marchywka_at_[hidden])
Date: 2008-03-17 11:16:36

I don't have a specific reference and I am not pushing any particular company but Intel
has developed some good online resources to help people use their hyperthreading product.
They have a lot of pdf files but I guess they want you to buy their intro book,

http://softwarecommunity.intel.com/articles/eng/1567.htm

Rule 6 here may answer your immediate question,

http://softwarecommunity.intel.com/articles/eng/1607.htm

I also saw something on google about FFTW that mentions multi-threading. IF you are interested
in efficient numerical stuff more generally, their site may be worth some time.

Mike Marchywka
586 Saint James Walk
Marietta GA 30067-7165
404-788-1216 (C)<- leave message
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marchywka_at_[hidden]
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Please indicate any concerns if applicable.
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ISP - try  me on marchywka_at_[hidden] if no reply
here. Thanks.

> From: hal_at_[hidden]
> To: boost-users_at_[hidden]
> Date: Mon, 17 Mar 2008 09:42:46 -0400
> Subject: [Boost-users] Threads Don't Take Turns Under Linux (Ubuntu Gutsy Gibbon)
>
> I apologize if this gets posted more than once. I found the group on
> GMane, tried to post, joined the email list, then tried to post several
> times but still have yet to see it show up.
>
> I'm learning C++ and found a tutorial on threads with Boost on Dr.
> Dobb's site.  I've copied the code from this url:
>
>  http://www.ddj.com/cpp/184401518?pgno=5
>
> It's supposed to fill a buffer with data on one thread and remove data
> on the other thread.  I would expect it to add data and remove at
> almost the same time but when I run it, it adds 10 items, then removes
> them, then adds ten again, and so on.  It's never adding and removing
> in an "interleaved" fashion.  I've also tried the same with simple
> counters where both threads count to ten, but it doesn't seem to make a
> difference.  It seems no matter how I set it up, one thread either
> completes, or runs until it has to stop for a mutex, then the other
> thread runs.  It seems that there is never a case of both threads
> running at the same time.  I've never had trouble doing this in Perl
> with fork() so I'm not at all sure what could be going wrong.
>
> As I said, it's not just the program below, it seems to be any program
> that uses more than one thread.
>
> Am I doing something wrong or is there a setting I need to change?
>
> I'm compiling it with "g++ -lboost_thread mthrd.cpp -o mthrd
> && ./mthrd";
>
> Thanks!
>
> Hal
> ------
> #include 
> #include 
> #include 
> #include 
>
> const int BUF_SIZE = 10;
> const int ITERS = 100;
>
> boost::mutex io_mutex;
>
> class buffer
> {
> public:
>   typedef boost::mutex::scoped_lock
>     scoped_lock;
>
>   buffer()
>     : p(0), c(0), full(0)
>   {
>   }
>
>   void put(int m)
>   {
>     scoped_lock lock(mutex);
>     if (full == BUF_SIZE)
>     {
>       {
>         boost::mutex::scoped_lock
>           lock(io_mutex);
>         std::cout <<
>           "Buffer is full. Waiting..."
>           << std::endl;
>       }
>       while (full == BUF_SIZE)
>         cond.wait(lock);
>     }
>     buf[p] = m;
>     p = (p+1) % BUF_SIZE;
>     ++full;
>     cond.notify_one();
>   }
>
>   int get()
>   {
>     scoped_lock lk(mutex);
>     if (full == 0)
>     {
>       {
>         boost::mutex::scoped_lock
>           lock(io_mutex);
>         std::cout <<
>           "Buffer is empty. Waiting..."
>           << std::endl;
>       }
>       while (full == 0)
>         cond.wait(lk);
>     }
>     int i = buf[c];
>     c = (c+1) % BUF_SIZE;
>     --full;
>     cond.notify_one();
>     return i;
>   }
>
> private:
>   boost::mutex mutex;
>   boost::condition cond;
>   unsigned int p, c, full;
>   int buf[BUF_SIZE];
> };
>
> buffer buf;
>
> void writer()
> {
>   for (int n = 0; n < ITERS; ++n)
>   {
>     {
>       boost::mutex::scoped_lock
>         lock(io_mutex);
>       std::cout << "sending: "
>         << n << std::endl;
>     }
>     buf.put(n);
>   }
> }
>
> void reader()
> {
>   for (int x = 0; x < ITERS; ++x)
>   {
>     int n = buf.get();
>     {
>       boost::mutex::scoped_lock
>         lock(io_mutex);
>       std::cout << "received: "
>         << n << std::endl;
>     }
>   }
> }
>
> int main(int argc, char* argv[])
> {
>   boost::thread thrd1(&reader);
>   boost::thread thrd2(&writer);
>   thrd1.join();
>   thrd2.join();
>   return 0;
> }
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users

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