Re: [Boost-users] thread mutex problem

Subject: Re: [Boost-users] thread mutex problem
From: Philipp Kraus (philipp.kraus_at_[hidden])
Date: 2010-09-07 04:19:27

On 2010-09-06 23:49:45 +0200, Anthony Williams said:

> Kraus Philipp <philipp.kraus_at_[hidden]> writes:
> 
>> I'm new with boost thread, I have some problems.
>> I have got two methods, one for writing and one for reading my data and I would
>> do this thread-safe.
>> I have tried to do this with boost::unique_lock<boost::shared_mutex> lock(...),
>> but I have created a deadlock.
>> 
>> For example my methods are called within the threads and set / get data to /
>> from a ublas matrix.
> 
>> How can I do both methods in the correct way thread-safe? 
> 
> boost::mutex m;
> 
> void setData( const size_t row, const size_t col, const size_t data) {
>     boost::unique_lock<boost::mutex> lk(m);
>     _matrix(row, col) = data 
> }
> 
> void getData( const size_t row, const size_t col, size_t& a, size_t& b) {
>     boost::unique_lock<boost::mutex> lk(m);
>     a = _matrix(row, col);
>     b = _matrix(col, row);
> }
> 
> Once you've got the basics working, you can change the mutex to a
> boost::shared_mutex and the lock in getData to a shared_lock rather than
> a unique_lock if profiling determines that this is the bottle neck, *and*
> the shared_mutex helps.

Thanks, but I have tried with the shared mutex like:

setData:
{
boost::unique_lock<boost::shared_mutex> lock( _matrixlock ); 
_matrix(row, col) = data 
}

getData:
{
boost::shared_lock<boost::shared_mutex> lock( _matrixlock );
 a = _matrix(row, col);
 b = _matrix(col, row);
}

I use the same lock mechanism for a ublas::vector<std::size_t> with a 
new mutex variable (_vectorlock), it seams there is an error. Is there 
a problem if I use two different mutex? I have got two member variables 
(the matrix and a vector) that must be thread-safe (not at the same 
time).

If I debug the executable with helgrind I'll get 
==939== Thread #1: Bug in libpthread: recursive write lock granted on 
mutex/wrlock which does not support recursion
==939==    at 0x513FC: pthread_cond_wait* (hg_intercepts.c:653)
==939==    by 0x19D3B7: boost::thread::join() (inlibboost_thread.dylib)
==939==    by 0x1683C: boost::thread_group::join_all() (in ./main)
==939==    by 0x17E6D: symmetric(std::vector<std::string, 
std::allocator<std::string> > const&, bool const&) (in ./main)
==939==    by 0x25D2: main (in ./main)

Thanks

Phil