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

Subject: Re: [Boost-users] [thread]Is shared_mutex recursive with respect to shared locks?
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2008-12-29 13:59:19

AMDG

Ken Savela wrote:
> 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?
>   

Yes this is the expected behavior.  When you try to upgrade the second
shared lock it blocks until the other shared_lock is released.  i.e. never.

In Christ,
Steven Watanabe