Re: [Boost-users] [boost-thread] error in the docs???

19 Mar 2009

      AMDG

Ovanes Markarian wrote:
...
Did you test it? In my case wait returns when the predicate is false. I use
an empty circular buffer and call from the same thread this code:
using namespace boost;
scoped_lock lock(mutex_);
        wait_for_free_slots_.wait(lock, bind(&buffer_type::full, buffer_));
//wait_for_free_slots_ is a condition variable
buffer_.push_back(item);
        wait_for_items_.notify_all();
This line returns immediately
wait_for_free_slots_.wait(lock, bind(&buffer_type::full, buffer_));
//wait_for_free_slots_ is a condition variable
If you inverse the predicate it blocks forever.
Seems to work for me

#include 
#include 
#include 
#include 
#include 

boost::mutex m;
boost::condition_variable c;

bool value = false;

void set() {
    boost::unique_lockboost::mutex l(m);
    value = true;
    c.notify_one();
}

void wait() {
    boost::unique_lockboost::mutex l(m);
    c.wait(l, boost::lambda::var(value));
}

int main() {
    boost::thread(wait);
    boost::this_thread::sleep(boost::posix_time::seconds(1));
    set();
}

Look at the definition of wait:

template<typename predicate_type>
void wait(unique_lock<mutex>& m,predicate_type pred)
{
    while(!pred()) wait(m);
}

In Christ,
Steven Watanabe