How do I make a critical section with Boost?

Question

For my cross-platform application I have started to use Boost, but I can't understand how I can implement code to reproduce behavior of Win32's critical section or .Net's lock.

I want to write a method Foo that can be called from different threads to control write operations to shared fields. Recursive calls within the same thread should be allowed (Foo() -> Foo()).

In C# this implementation is very simple:

object _synch = new object();
void Foo()
{
    lock (_synch)  // one thread can't be lock by him self, but another threads must wait untill
    {
        // do some works
        if (...) 
        {
           Foo();
        }
    }
}

Answer 1

With boost you can use boost::lock_guard<> class:

class test
{
public:
 void testMethod()
 {
  // this section is not locked
  {
   boost::lock_guard<boost::recursive_mutex> lock(m_guard);
   // this section is locked
  }
  // this section is not locked
 }
private:
    boost::recursive_mutex m_guard;
};

PS These classes located in Boost.Thread library.

Answer 2

Here's a rewrite of your example, using Boost.Thread: I removed the comments, but otherwise, it should be a 1-to-1 rewrite.

boost::recursive_mutex mtx;

void Foo()
{
    boost::lock_guard<boost::recursive_mutex> lock(mtx);
    if (...) 
    {
       Foo();
    }
}

The documentation can be found here.

Note that Boost defines a number of different mutex types. Because your example shows the lock being taken recursively, we need to use at least boost::recursive_mutex.

There are also different types of locks. In particular, if you want a reader-writer lock (so that multiple readers can hold the lock simultaneously, as long as no writer has the lock), you can use boost::shared_lock instead of lock_guard.