如何使函数线程安全

Question

i have a class say Graph

class Graph
{
    bool* visited;
    void myfun ()
    {
        visited = new bool[10];
        for (int i=0;i<10;i++)
            visited[i]=false;

            myfunc2 ();
    }
    void myfunc2 ()
    {
        // Assume this changes the visited array
    }

} 

Now if i call the myfunc () in different threads then they would be working independtly and will change the visited array independetly.....this would make things go wrong.....

How do i deal with things like this while making a graph library of my own...?

Answer 1

If your threads has an own instance of "Graph", then you do not need thread safety because each thread accesses a different memory area.

But if you share the array between multiple threads:

Use locking (mutex, semaphore), synchronisation or inter-thread communication.

Lock the visited array, eg. std::lock, boost::mutex (or platform specific locking like pthread mutex). And try to lock the data, not the code.

somelock.lock();
visited[i]=false; //global array
somelock.unlock();