A bug in gsHDomainBoundaryIterator.h when using openMP.

[wj902911]

https://github.com/gismo/gismo/blob/74b2d0c85407013d35bf6d07192c6954868acd3d/src/gsHSplines/gsHDomainBoundaryIterator.h#L98C48-L98C48
This will cause the iterator go outside the domain when using openMP.

[wj902911]

I found the problem will happen only when iterating through boundaries, so I compared the implementation btween gsHDomainBoundaryIterator.h and gsHDomainIterator.h. I noticed that the next() function in gsHDomainIterator.h (Line 93) has a different implementation with the one in gsHDomainBoundaryIterator.h (Line 96).
In gsHDomainIterator.h:

bool next(index_t increment)
    {
        for (index_t i = 0; i != increment && this->m_isGood; ++i)
        {
            this->m_isGood = nextLexicographic(m_curElement, m_meshStart, m_meshEnd);
            if (!this->m_isGood)
                this->m_isGood = nextLeaf();
        }

        if (this->m_isGood)
            updateElement();

        m_id += increment; //increment id
        return this->m_isGood;
    }

In gsHDomainBoundaryIterator.h:

bool next(index_t increment)
    {
        for (index_t i = 0; i < increment; i++)
            this->m_isGood = nextLexicographic(m_curElement, m_meshStart, m_meshEnd);

        if (this->m_isGood) // new element in m_leaf
            updateElement();
        else // went through all elements in m_leaf
            this->m_isGood = nextLeaf();

        return this->m_isGood;
    }

Finally, by replacing Line 9899 in gsHDomainBoundaryIterator.h with Line 95100 in gsHDomainIterator.h, this issue can be fixed. Although this works for me now, I don't know if it will cause some other issues in the future.
Modified next() in gsHDomainBoundaryIterator.h:

bool next(index_t increment)
    {
        /*
        for (index_t i = 0; i < increment; i++)
            this->m_isGood = nextLexicographic(m_curElement, m_meshStart, m_meshEnd);
        */
        for (index_t i = 0; i != increment && this->m_isGood; ++i)
        {
            this->m_isGood = nextLexicographic(m_curElement, m_meshStart, m_meshEnd);
            if (!this->m_isGood)
                this->m_isGood = nextLeaf();
        }

        if (this->m_isGood) // new element in m_leaf
            updateElement();
        else // went through all elements in m_leaf
            this->m_isGood = nextLeaf();

        return this->m_isGood;
    }