January 01, 2003
Multithreaded Programming with the Command Pattern
Multithreaded Programming with the Command Pattern
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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