circular buffer using mutex

Question

This was from compsci lecture quiz that my professor want us to challenge. he said that this class is about circular buffer but has got major problem. I've try to think for whole day but have no clue. please give me some ideas

#include <stdint.h>
#include <boost/thread.hpp>

template <typename T, uint32_t max>
class CircularBuffer
{
public:

    CircularBuffer() : m_WriteOffset(0), m_ReadOffset(0){}
    ~CircularBuffer(){};

    void push( T val )
    {
        boost::lock_guard<boost::mutex> guard( m_Mutex );
        m_Buffer[m_WriteOffset++] = val;
    }

    T pull()
    {
        boost::lock_guard<boost::mutex> guard( m_Mutex );
        return m_Buffer[m_ReadOffset++];
    }

private:

    boost::mutex m_Mutex;

    enum { MAX_SIZE = max };
    T m_Buffer[MAX_SIZE];
    uint32_t m_WriteOffset;
    uint32_t m_ReadOffset;
};

To give you a hint: There is a superfluous semicolon in the code. Then, write a test with two threads, one writing N elements with a pattern, the other reading N elements and verifying the pattern. — Ulrich Eckhardt, Aug 21 '13 at 05:54
...and use std::thread, but that assumes you have a C++11 compiler. — Ulrich Eckhardt, Aug 21 '13 at 05:56
If you don't know what a `mutex` and what a `lock_guard` is, then better research that first. This is basic knowledge at the level of your problem. — Walter, Sep 03 '13 at 15:48

score 1 · Accepted Answer · answered Aug 21 '13 at 05:54

1

full, empty methods not implemented. Offset increment must be like m_ReadOffset = (m_ReadOffset + 1) % MAX_SIZE, then only the buffer will be circular. Both read and write offset I mean.

answered Aug 21 '13 at 05:54

Sakthi Kumar

3,047
15
28

can I ask you how lock_guard works inside of the function? I know how mutex works but not with boost functions. – user842589 Aug 21 '13 at 06:13
sorry that I could not answer your question. I actually don't know C++, just answered the logical part of a data structure. – Sakthi Kumar Aug 21 '13 at 06:31

score 0 · Answer 2 · answered Aug 21 '13 at 06:03

0

You asked for a hint, so here is one:

What happens if you push MAX_SIZE+1 elements before reading any?

answered Aug 21 '13 at 06:03

Ross Bencina

3,822
1
19
33

thanks, don't really understand how mutex and lock_guard functions works so I was kind of lost what is the main problem. – user842589 Aug 21 '13 at 06:11
the lock guard just locks the mutex, and unlocks it when it goes out of scope. – Ross Bencina Aug 21 '13 at 08:00

circular buffer using mutex

2 Answers2