Question

I am new to multithread programming, please don’t laugh if this seems too simple.

I have a simple class object which has several member variables, e.g.,

class XYZ
{
public:
int a;
int b;
...
};

xyz is a shared objects among multiple threads, what’s the best way to share “a” among multiple threads? For example,

In thread A, I will do something like

xyz.a = xyz.a + rand();

In thread B, I will do something like

xyz.a = xyz.a - rand();

I heard about create a mutex as a class member, can someone please give a simple example how to do that.

How can I create a class interface which allows multiple threads to safely access its member?

Answer 1

You can use a mutex. They can be locked by only one thread simultaneously.

class XYZ
{
    int a,b;
    boost::mutex mutex;
}

Then use for the thread code

void thread(XYZ *xyz)
{
  //....

  // now a member of xyz should be accessed/changed.
  { 
    boost::unique_lock<boost::mutex> lock(xyz->mutex); // lock first the mutex
    // do something with members of xyz
    // ...
  } // mutex automatically freed because lock object destroyed

  //...
 }