[Boost-users] Probably bug in condition::timed_wait()

20 Sep 2006

      Hi,

I'm porting custom library from UNIX to Windows and found that some 
piece of code work correctly on UNIX and some time segfaulting  on 
Windows. I think, that problem is on boost::condition::timed_wait() 
function. To be sure I write small test:

#include <stdexcept>
#include <iostream>

#include <boost/thread.hpp>

#include <windows.h>

using namespace boost;
using namespace std;

class AsyncQueue {
public:
    AsyncQueue() : m_counter(0) {}

    void push()
    {
        mutex::scoped_lock lock(m_mutex);
        m_counter++;
        m_condition.notify_one();
    }

    void timed_pop(const xtime &time)
    {
        mutex::scoped_lock lock(m_mutex);

        if(m_counter) {
            m_counter--;
            return;
        }

        if(!m_condition.timed_wait(lock, time)) return;

        if(!m_counter) throw out_of_range("oops...");

        m_counter--;
    }

private:
    mutex m_mutex;
    condition m_condition;

    int m_counter;
};

static AsyncQueue queue;

static void start()
{
    for(;;) {
        queue.push();
        Sleep(100);
    }
}

int main(int argc, char **argv)
{
    thread thread(start);

    xtime time;

    for(;;) {
        xtime_get(&time, TIME_UTC);
        time.nsec += 10000;
        queue.timed_pop(time);
    }

    return 0;
}

AsyncQueue is a simple asynchronous queue container with two operations 
- push() and timed_pop(). Because this is test, AsyncQueue don't really 
collect something, but it's has variable (m_counter field) that count 
current number on elements in container. When push() called m_counter 
incremented and when timed_pop() "virtually" remove item from queue 
m_counter decremented.

In main() I create additional thread, which push data to queue. Data 
popped from queue in main thread by calling timed_pop(). But sometimes 
timed_pop throw out_of_range exception. If you look in code you can see 
that it's mean that condition::timed_wait() return true, but queue is empty!

I look to boost-users list and found e-mail's about similar problems 
from Eric Colleu, but decision wasn't found.

Two words about my environment. I use Visual Studio 2005, Windows XP SP2 
on VMWare 5.5.1. Boost version is 1.33.1.

Thanks for constructive answers.

[Boost-users] Probably bug in condition::timed_wait()

Pavel Syomin