Typical usage of the last two constructs is demonstrated as follows:

#include <ext/concurrence.h>

namespace
{
  __gnu_cxx::__mutex safe_base_mutex;
} // anonymous namespace

namespace other
{
  void
  foo()
  {
    __gnu_cxx::__scoped_lock sentry(safe_base_mutex);
    for (int i = 0; i < max;  ++i)
      {
	_Safe_iterator_base* __old = __iter;
	__iter = __iter-<_M_next;
	__old-<_M_detach_single();
      }
}

In this sample code, an anonymous namespace is used to keep the __mutex private to the compilation unit, and __scoped_lock is used to guard access to the critical section within the for loop, locking the mutex on creation and freeing the mutex as control moves out of this block.

Several exception classes are used to keep track of concurrence-related errors. These classes are: __concurrence_lock_error, __concurrence_unlock_error, __concurrence_wait_error, and __concurrence_broadcast_error.