Deadlock prevention techniques

1. Choose the lock order by address

The simplest technique in these cases is to always lock the mutexes in ascending order of address:

void lock(boost::mutex& m1,boost::mutex& m2)
{
    if(&m1<&m2)
    {
        m1.lock();
        m2.lock();
    }
    else
    {
        m2.lock();
        m1.lock();
    }
}

2. Order mutexes "naturally", with try-and-back-off

If the mutexes cannot be ordered by address (for whatever reason), then an alternative scheme must be found. One such scheme is to use a try-and-back-off algorithm: try and lock each mutex in turn; if any cannot be locked, unlock the others and start again. The simplest implementation for 3 mutexes looks like this:

void lock(boost::mutex& m1,boost::mutex& m2,boost::mutex& m3)
{
    do
    {
        m1.lock();
        if(m2.try_lock())
        {
            if(m3.try_lock())
            {
                return;
            }
            m2.unlock();
        }
        m1.unlock();
    }
    while(true);
}