[boost] Problems with conditions in boost::thread

26 Jun 2004

      Hi, 
I just started to use boost::thread in a bigger application. Since the
condition variables do not work as expected - e.g. the waiting thread
never wakes up ( example can be found here: 
 http://svn.zynot.org/svn/zynot/projects/xeta/trunk/source/src/xeta/curl.cpp )
- I started writing a smaller test case to see if I use the library
correctly. That little test application works fine if I run it in with
the gnu debugger, and if I have debugging symbols in my glibc. In all
other cases the process gets terminated before any debuging print outs
show up or the debugger fails to run the application:

#include <list>
#include <iostream>
#include <boost/bind.hpp>
#include <boost/thread/xtime.hpp>
#include <boost/thread/thread.hpp>
using namespace boost;

struct Mini {
  bool running;
  thread worker;
  mutex list_mutex;
  condition items_empty;
  std::list<std::string> items;

  typedef mutex::scoped_lock lock;

  Mini();
  ~Mini();
  void run();
  void add( std::string const& item);
};

Mini::Mini() : worker( bind( &Mini::run, this ) )  { }

Mini::~Mini() {
  running = false; 
  {
    lock the_list( list_mutex );
    items_empty.notify_one();
  }
  worker.join();
}

void Mini::run() {
  running = true;
  while( running )   {
    lock the_list( list_mutex );
    if( running && items.empty() )     {
      std::cout << "Waiting for item" <<   std::endl; 
      items_empty.wait( the_list   );
      std::cout << "Continue" <<   std::endl;
    } 
    std::cout << "Removing :" << items.front() << std::endl;
    items.pop_front();
  }
}

void Mini::add( std::string const& item ) {
  lock list_access( list_mutex );
  std::cout << "Adding :" << item << std::endl;
  items.push_back( item );
  std::cout << "Notifying other thread" << std::endl;
  items_empty.notify_one();
}

int main() {
  Mini my_mini;
  my_mini.add("Once upon a time");
  my_mini.add("there was a little mouse");
  my_mini.add("that lived in a little house");

  xtime xt;
  xtime_get(&xt, TIME_UTC);
  xt.sec += 2;

  thread::sleep(xt);
}

After that I tried to do it without boost. This time everything works as
expected, with and without debugger. 
#include <list>
#include <unistd.h>
#include <iostream>
#include <pthread.h>

struct Mini {
  bool running;
  pthread_t worker;
  pthread_mutex_t mutex;
  pthread_cond_t not_empty;
  std::list<std::string> items;

  Mini();
  ~Mini();
  static void * call_run( void *);
  void run();
  void add( std::string const& item);
};

void* Mini::call_run( void * ptr)
{
  static_cast<Mini*>(ptr)->run();
  return 0;
}

Mini::Mini() 
{
  pthread_mutex_t temp_mut = PTHREAD_MUTEX_INITIALIZER;
  mutex = temp_mut;
  pthread_cond_t temp_cond = PTHREAD_COND_INITIALIZER;
  not_empty = temp_cond;
  worker = pthread_create( &worker, 0,
      Mini::call_run, this );
}

Mini::~Mini()
{
  running = false;
  {
    pthread_mutex_lock( &mutex );
    pthread_cond_broadcast( ¬_empty );
    pthread_mutex_unlock( &mutex );
  }
  pthread_join( worker, 0 );
  pthread_cond_destroy( ¬_empty );
}

void Mini::run()
{
  running = true;
  while( running )
  {
    pthread_mutex_lock( & mutex );
    if( running && items.empty() )
    {
      std::cout << "Waiting for item" << std::endl; 
      pthread_cond_wait(¬_empty, &mutex);
      std::cout << "Continue" << std::endl;
    }
    std::cout << "Removing :" << items.front() << std::endl;
    items.pop_front();
    pthread_mutex_unlock( &mutex );
  }
}

void Mini::add( std::string const& item )
{
  pthread_mutex_lock( & mutex );
  std::cout << "Adding :" << item << std::endl;
  items.push_back( item );
  std::cout << "Notifying other thread" << std::endl;
  pthread_cond_broadcast(& not_empty);
  pthread_mutex_unlock( &mutex );
}

int main()
{
  Mini my_mini;
  my_mini.add("Once upon a time");
  my_mini.add("there was a little mouse");
  my_mini.add("that lived in a little house");

  sleep(2 );
}

Any ideas?

[boost] Problems with conditions in boost::thread

Andreas Pokorny