Async programming with C++11

Problem

1. write 2 functions A and B
2. Function A goes on for a long long time
3. Function B performs a short simple task
4. Start executing function A
5. Invoke B from A
6. A keeps on running while B doing its job
7. at some point when B finishes A acknowledges it and continues doing its processing

Equipment used

1. Ubuntu 10.04 to 12.04: i have tried it on most of the Ubuntu versions
2. g++ 4.6: this is the only compiler that i have tried this on, 10.04 comes with g++4.4 by default in which case you need to install the new version using apt-get install g++-4.6.
3. A text editor

Async programming with C++11

#include <future>
#include <iostream>

using namespace std;

bool finito = false;//this is the shared variable which will pass messages between the 2 functions
int value;
mutex m; // mutex is simply a way to enforce locking on a shared piece of data

bool countToTen()//think of this as the function B
{
     /*lets do something so we can demonstrate that the function takes
     time to finish*/
  for(int counter=0;counter<10;counter++)
  {
     / /cout<<"counter from(async):"<<(i+1)<<endl;
  }
   /*lets acquire a lock on the finito variable
   we do not need to worry about unlocking it
   as the lock_guard already takes care of that for us
   */
   lock_guard<std::mutex> lk(m);
   finito = true;
   return finito;
}

int main()//think of this as the function A
{
   /*the launch policies are launch::async and launch::sync
   which are both self-explanatory.
   */   
   future<bool> done = async(std::launch::async,countToTen);
   cout<<"Now we are going to start counting...."<<endl;
   for(int counter=0;counter<100000;counter++)
   {
      /*do something meaningfull....
        In my case i was looping through frames of a video
      */

     /*  Instead of accessing finito directly we can also access it via the future
         done.get(), the future is a neat little thing that holds the return value of your 
         function, so when the function is done you can access it via the get method
     */

      if(finito)
      {
          value+=counter;
          cout<<"ok so we have finished the function"<<endl;
          cout<<"this is where we got upto:"<<value<<" before countToTen finished";
          cout<<endl;
         break;//ok we are done so lets get out of here
      }
   }
}

Compiling the code above

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