Re: [Boost-users] Several novice questions concerning threading

Subject: Re: [Boost-users] Several novice questions concerning threading
From: Master (master.huricane_at_[hidden])
Date: 2012-04-12 05:24:41

i modified an example <http://en.highscore.de/cpp/boost/>, but i dont know
why it gets locked!

> #define BOOST_THREAD_USE_LIB
> #include <iostream>
> #include <boost/thread.hpp>
> #include <vector>
> using namespace std;
>
> vector<int> someSharedResource;
> boost::mutex mutex;
> boost::condition_variable_any condition;
> void Writer()
> {
>
>
>     for (int i = 0; i < 10 ; i++)
>         {
>            boost::unique_lock<boost::mutex> locker(mutex);
>            someSharedResource.push_back(i);
>           // cout<<boost::this_thread::get_id()<<"\t"<<endl;
>            condition.notify_all();
>            condition.wait(mutex);
>         }
>
> }
> void Reader()
> {
>     int counted_items=0;
>    for( int i =0;i<10;i++)
>         {
>                boost::unique_lock<boost::mutex> locker(mutex);
>                condition.wait(mutex);
>
> cout<<someSharedResource.back()<<"\t"<<boost::this_thread::get_id()<<endl;
>                 counted_items++;
>                 condition.notify_all();
>         }
>
>
> }
> int main()
> {
>   boost::thread t1(Writer);
>   boost::thread t2(Reader);
>   t1.join();
>   t2.join();
> }
>
 is it not that , the mutex is not released until the writer function ,
gets passed the wait(mutex) method ? and after that waits for the mutex ?
and inside reader function , when it is awakened by the notify_all() method
by writer function , it waits until writer releases the mutex and then it
owns it and there it executes .
so why do i fell into a locked down of some kind .
if i run this example couple of times , some times it works fine and some
times it just hangs at the beginning ( getting locked ? ) whats wrong with
it . ?