[Boost-users] [threads] read_write_mutex and condtion

From: Phil Endecott (spam_from_boost_users_at_[hidden])
Date: 2005-10-30 06:44:10

Dear All,

Is it possible to use a boost::condition in combination with a 
read_write_mutex?  I've tried but failed.  This is with 1.32.0.  My test 
code follows.  As you can see it can use either a mutex or a 
read_write_mutex depending on which bits are commented-out.  It works as 
expected with a mutex, but with a read_write_mutex I get a compiler 
error, shown below.

Perhaps I am missing some fundamental reason why conditions can't work 
with read_write_mutexes.  Can someone explain?

Thanks,  Phil.

#include <string>
#include <iostream>
#include <boost/thread/mutex.hpp>
#include <boost/thread/read_write_mutex.hpp>
#include <boost/thread/condition.hpp>
#include <boost/thread/thread.hpp>
#include <boost/bind.hpp>
#include <unistd.h>

using namespace std;
using namespace boost;

struct shared_thing {

   string data;
   //typedef mutex mx_t;
   //typedef mutex::scoped_lock read_lock;
   //typedef mutex::scoped_lock write_lock;

   typedef read_write_mutex mx_t;
   typedef read_write_mutex::scoped_read_lock read_lock;
   typedef read_write_mutex::scoped_write_lock write_lock;

   mx_t mx;
   condition cn;

   shared_thing::shared_thing(void):
     //mx()
     mx(read_write_scheduling_policy::writer_priority)
   {}

   void writer(void)
   {
     while(1) {
       sleep(1);
       {
        write_lock l(mx);
        data += ".";
        cn.notify_all();
       }
     }
   }

   void reader(void)
   {
     while(1) {
       read_lock l(mx);
       cn.wait(l);
       cout << data << endl;
     }
   }
};

int main(int argc, char* argv[])
{
   shared_thing t;
   thread wr_thread(bind(&shared_thing::writer,&t));
   t.reader();
}

$ g++ -pthread -O -Wall -o condvar condvar.cc -lboost_thread
/usr/include/boost/thread/detail/read_write_lock.hpp: In member function 
`void
    boost::condition::wait(L&) [with L =
    boost::detail::thread::scoped_read_lock<boost::read_write_mutex>]':
condvar.cc:51:   instantiated from here
/usr/include/boost/thread/detail/read_write_lock.hpp:297: error: `
 
boost::read_write_mutex&boost::detail::thread::scoped_read_lock<boost::read_write_mutex>::m_mutex
    ' is private
/usr/include/boost/thread/condition.hpp:92: error: within this context