Question

I am looking for the best way to solve the following (c++) problem. I have a function given by some framework, which returns an object. Sometimes it takes just miliseconds, but on some occasions it takes minutes. So i want to stop the execution if it takes longer than let’s say 2 seconds.
I was thinking about doing it with boost threads. Important sidenote, if the function returns faster than the 2 seconds the program should not wait.
So i was thinking about 2 threads:

1.thread: execute function a       
2.thread: run timer                
if(thread 2 exited bevore thread 1) kill thread 1 
else do nothing

I am struggeling a bit the practical implementation. Especially,

• how do i return an object from a child boost thread to the main thread?
• how do i kill a thread in boost?
• is my idea even a good one, is there a better way to solve the problem in c++ (with or without boost)?

Answer 1

As for waiting, just use thread::timed_join() inside your main thread, this will return false, if the thread didn’t complete within the given time.

Killing the thread is not feasible if your third-party library is not aware of boost:threads. Also, you almost certainly don’t want to ‘kill’ the thread without giving the function the possibility to clean up.

I’d suggest that you wait for, say, 2 seconds and then continue with some kind of error message, letting the framework function finish its work and just ignoring the result if it came too late.

As for returning a value, I’d suggest something like

struct myfunction {
   MyObj returnValue;
   void operator() () { 
     // ... 
     returnValue = theComputedReturnValue;
   }
};

// ...
myfunction f;
boost::thread t = boost::thread(boost::ref(f));
t.join(); // or t.timed_join()...
use(f.returnValue); 
// ...