[Boost-users] Thread object pointers.

Subject: [Boost-users] Thread object pointers.
From: Albert Schueller (schuelaw_at_[hidden])
Date: 2010-08-03 17:10:54

Tue Aug  3 14:10:04 PDT 2010

Hi all,

I'm trying to get up to speed on libboost's thread class using the
tutorial information here:

http://www.drdobbs.com/cpp/184401518

I'm curious why the two programs below seem to behave differently.  In
LISTING 1, three threads are declared as thrd1, thrd2, and thrd3 explicitly
and each loops 10 times with random length sleeps.

LISTING 2 is identical, except for the fact the three thread variables
are allocated to boost::thread pointers.

When I run LISTING 1 it appears that the threads are acting
independently as I would hope.  When I run LISTING 2, it seems that the
threads are not independent, but rather thrd1 does its job, followed by
thrd2, followed by thrd3.

Am I not locking properly?

Any help would be appreciated.

Albert

///////////////////////////////////////////////////////////////////////////
//LISTING 1

#include <boost/thread/thread.hpp>
#include <boost/thread/mutex.hpp>
#include <iostream>
#include <unistd.h>
#include <cstdlib>

boost::mutex io_mutex;

struct count
{
  count(int id) : id(id) { }

  void operator()()
  {
    int upause;
    for (int i = 0; i < 10; ++i)
    {
      upause = rand()%1000000;
      usleep(upause);
      boost::mutex::scoped_lock
        lock(io_mutex);
      std::cout << id << ": "
        << i << " paused " << upause << std::endl;
    }
  }

  int id;
};

int main(int argc, char* argv[])
{
  boost::thread thrd1(count(1));
  boost::thread thrd2(count(2));
  boost::thread thrd3(count(3));
  thrd1.join();
  thrd2.join();
  thrd3.join();
  return 0;
}

///////////////////////////////////////////////////////////////////////////
//LISTING 2

#include <boost/thread/thread.hpp>
#include <boost/thread/mutex.hpp>
#include <iostream>
#include <unistd.h>
#include <cstdlib>

boost::mutex io_mutex;

struct count
{
  count(int id) : id(id) { }

  void operator()()
  {
    int upause;
    for (int i = 0; i < 10; ++i)
    {
      upause = rand()%1000000;
      usleep(upause);
      boost::mutex::scoped_lock
        lock(io_mutex);
      std::cout << id << ": "
        << i << "paused (" << upause << ")" << std::endl;
    }
  }

  int id;
};

int main(int argc, char* argv[])
{
  int i;
  int num_thrds = 3;
  boost::thread *thrd[4];

  for(i=0;i<num_thrds;i++) {
   thrd[i] = new boost::thread(count(i+1));
   thrd[i]->join();
  }

  // deallocate thread objects
  for(i=0;i<num_thrds;i++) {
    delete thrd[i];
  }

  return 0;
}