[Boost-users] [thread]Is shared_mutex recursive with respect to shared locks?

Subject: [Boost-users] [thread]Is shared_mutex recursive with respect to shared locks?
From: Ken Savela (ksavela_at_[hidden])
Date: 2008-12-29 10:25:40

In other words, should the following code result in a deadlock?

#include <iostream>

#include <boost/thread.hpp>

int main(int argc, char* argv[])
{
   boost::shared_mutex smx;

   boost::upgrade_lock<boost::shared_mutex> lock_one(smx);
   std::cout << "Locked once." << std::endl;
   std::cout.flush();
   boost::upgrade_lock<boost::shared_mutex> lock_two(smx);
   std::cout << "Locked again." << std::endl;
   std::cout.flush();
   boost::upgrade_to_unique_lock<boost::shared_mutex> lock_three(lock_two);
   std::cout << "Write lock." << std::endl;

   return 0;
}

This example illustrates the problem I'm having in my app -- I have a 
situation where a single thread may end up performing more than a single 
shared lock.  When it does so, it hangs on the nested upgrade_lock.  Is this 
the expected behavior?