Multithreading with Inheritance (C++) - c++

Question

I am trying to call the "Run" function in a new thread. Right now, I have this code using openMP that doesn't actually run "Run" in a new thread. NOTE: I am not asking for help using OpenMP. This code was just a quick fix. I would prefer a CreateThread() method of going about this.
vector<ICommand*>* commands;
string strInput;
// For each command...
for(vector<ICommand*>::iterator i = commands->begin(); i != commands->end(); ++i)
{
// ...if the current command we're examining is valid...
if((*i)->ContainsCommand(strInput))
{
// ...run it in a new thread and don't let ZChatInput handle it normally...
#pragma omp sections nowait
{
#pragma omp section
(*i)->Run(strInput);
#pragma omp section
bRet = false;
}
// ...and don't check any more commands.
break;
}
}
So how would this be done using just standard and STL? Of course, I'm looking for a way that works :)

Answer 1

How about using Boost.Thread?
if((*i)->ContainsCommand(strInput))
{
boost::thread t( boost::bind( &ICommand::Run, *i ) );
}
This will run "Run" in a detached thread.
(Note, I did not test this.)

Answer 2

like this? http://msdn.microsoft.com/en-us/library/kdzttdcb(VS.80).aspx

Answer 3

You can try something like this:
vector<ICommand*>* commands;
string strInput;
void CommandOnThread(void* command)
{
(ICommand*)command->Run();
}
// For each command...
for(vector<ICommand*>::iterator i = commands->begin(); i != commands->end(); ++i)
{
// ...if the current command we're examining is valid...
if((*i)->ContainsCommand(strInput))
{
//Attach the input to the command
(*i)->AttachInput(strInput);
_beginthread(CommandOnThread, 0, *i);
break;
}
}
For this you have to change the command interface a little for passing the command input in two steps: first store the input in the command object and then call Run() without arguments. You can replace _beginthread with CreateThread if you like they are quite similar.
Just to clarify: You can't use an instance method as the function parameter for _beginthread (or CreateThread). The solution above is to pass the object (command) to the function and then call its instance method (Run). However in that case you can't pass extra arguments to the thread function, and therefore can't pass arguments to the instance method. The easiest solution for this is to somehow attach the argument to the instance before passing it to the thread function.
I hope this helps. Of course this solution is not possible if you can't change the interface and implementation of the Command class.

Answer 4

Do you really want to create a thread for each command? Thread creation is expensive.
If you absolutely need this part to be asynchronous - create a synchronized queue, pre-spawn number of threads (that's your scalability here,) have them block on the queue, then put a message (pointer?) onto the queue in your loop.
Answering your comment:
// setup
sync_queue wq; // that would be protected by mutex and a conditional var or two
for ( i = 0; i < parallel_factor; ++i ) start_thread( th_func, wq );
...
// your loop body :
...
if ( valid_input ) q.put( item );
...
// thread function
void th_func( sync_queue& q )
{
work_item* pwi;
while (( pwi = q.get())) do_it( pwi );
}
Makes sense?

Answer 5

So I figured it out after double-checking the MSDN documentation. Here's how I did it, in case any of you are interested:
static vector<ICommand*>* commands;
// This is what we pass to CommandOnThread.
struct CommandParameter
{
string strInput;
ICommand* command;
};
int CommandOnThread(CommandParameter* cp)
{
cp->command->Run(cp->strInput);
delete cp;
return 0;
}
void foo()
{
string strInput;
...
// For each command...
for(vector<ICommand*>::iterator i = commands->begin(); i != commands->end(); ++i)
{
// ...if the current command we're examining is valid...
if((*i)->ContainsCommand(strInput))
{
// Put the CP on the stack.
CommandParameter* temp = new CommandParameter;
if(temp == NULL)
{
Print("Out of memory!");
bRet = false;
break;
}
// ...set up the parameters to createthread...
temp->strInput = strInput;
temp->command = *i;
// ...run it in a new thread...
CreateThread(NULL, NULL, (LPTHREAD_START_ROUTINE)CommandOnThread, temp, NULL, NULL);
// ...and don't check any more commands.
bRet = false;
break;
}
}
}