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Listing 5 The threads call the Execute() function on the Commands that they receive

#include <iostream>

#include <vector>


#include <windows.h>


HANDLE condition;
HANDLE mutex;

class Command;

std::vector < Command* > queue;

// base command class
class Command
{
public:
  Command () {}
  ~Command () {}

  // the actual command logic resides in Execute ()
  virtual void Execute () = 0; 
};

class Command_A : public Command
{
public:
  Command_A () {}
  ~Command_A () {}

  void Execute () { std::cout << "Doing some work" << std::endl; }
};

class Command_B : public Command
{
public:
  Command_B () {}
  ~Command_B () {}

  void Execute () { std::cout << "Doing some other work" << std::endl; }
};

void thread_entry ()
{
  for ( ;; )
  {
    WaitForSingleObject ( mutex, INFINITE );
    if ( queue.empty () )
    {
	  ReleaseMutex ( mutex );

      std::cout << "thread going to sleep" << std::endl;

      WaitForSingleObject ( condition, INFINITE );

	  WaitForSingleObject ( mutex, INFINITE );

      std::cout << "thread awake" << std::endl;

    }

    if ( queue.empty () )
    {
      std::cout << "work queue is empty" << std::endl;

      ReleaseMutex ( mutex );

      continue;
    }

    Command* command = queue.back ();
    queue.pop_back ();
    ReleaseMutex ( mutex );


    command->Execute ();
    delete command;

    Sleep ( 1 );
  }
}

int main ()
{
  HANDLE threads[ 10 ];

  mutex = CreateMutex ( NULL, FALSE, NULL );

  condition = CreateEvent ( NULL, FALSE, FALSE, NULL );



  for ( int i = 10; i > 0; --i )
  {
    threads[ i - 1 ] = CreateThread ( NULL, 0,
                              ( LPTHREAD_START_ROUTINE ) thread_entry,
		         NULL, 0, NULL );

  }

  for ( int index = 10; index > 0; --index )
  {
    WaitForSingleObject ( mutex, INFINITE );

    Command* command = index % 2 ? ( Command* ) new Command_A
                                 : ( Command* ) new Command_B;
    queue.push_back ( command ); 
    SetEvent ( condition );

    ReleaseMutex ( mutex );

  }

  WaitForSingleObject ( threads[ 0 ], INFINITE );


  return ( 0 );
}

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