Question

I’ve been working lately on my own thread pool implementation, and it works fine( pretty much). The problem is it takes almost all CPU resources.
Please, take a look on my implementation:

ThreadPool.h

#include <vector>
#include <list>
#include <Windows.h>

const int DefaultThreadsNumber = 5;

class thread_pool
{
    typedef void ( *Task )( );

    void* m_hEvent;

    CRITICAL_SECTION m_hExecuteFunc;
    CRITICAL_SECTION m_hRunFunc;


    std::vector<void*> m_ThreadHandles;
    std::list<Task> m_TasksQueue;
    int m_nThreadInQueue;
    static unsigned __stdcall Run( void* thisParam );
public:
    thread_pool( int nMaxThreadNo );
    ~thread_pool();
    void Execute( Task task );
};

ThreadPool.cpp

#include "thread_pool.h"
#include <process.h>

void* g_hTaskFinishedEvent;

thread_pool::thread_pool( int nMaxThreadNo )
{
    if ( nMaxThreadNo <= 0 )
        nMaxThreadNo = DefaultThreadsNumber;

    m_nThreadInQueue = nMaxThreadNo;
    for( int i = 0; i < nMaxThreadNo; ++i )
    {
        m_ThreadHandles.push_back((void*)_beginthreadex(NULL, 0, &Run, (void*)this, 0, 0 ));
    }

    InitializeCriticalSection( &m_hExecuteFunc );
    InitializeCriticalSection( &m_hRunFunc );
}


thread_pool::~thread_pool()
{
    for ( std::vector<void*>::iterator it = m_ThreadHandles.begin(); 
            it != m_ThreadHandles.end(); 
            ++it )
    {
        CloseHandle( *it );
    }

    DeleteCriticalSection( &m_hExecuteFunc );
    DeleteCriticalSection( &m_hRunFunc );

}

void thread_pool::Execute( Task task )
{
    EnterCriticalSection( &m_hExecuteFunc );

    m_TasksQueue.push_back( task );

    LeaveCriticalSection( &m_hExecuteFunc );

    m_hEvent = CreateEvent(NULL, true, false, NULL);
    SetEvent( m_hEvent ); // TODO: what if setEvent will fail???
}

unsigned __stdcall thread_pool::Run(void* thisParam )
{
    thread_pool *This = (thread_pool*)thisParam;
    while(true)
    {
        WaitForSingleObject( This->m_hEvent, INFINITE );
        while(!This->m_TasksQueue.empty())
        {


            EnterCriticalSection( &This->m_hExecuteFunc );

            if ( !This->m_TasksQueue.empty() ) 
            {
                This->m_TasksQueue.front()();
                This->m_TasksQueue.pop_front();

                g_hTaskFinishedEvent = CreateEvent(NULL, true, false, NULL);
                SetEvent( g_hTaskFinishedEvent );
            }

            LeaveCriticalSection( &This->m_hExecuteFunc );
        }
    }
    return 0;
}

How can it be improved?

Thanks on advance.

Answer 1

In CreateEvent, bManualReset is set to true, but you’re not calling ResetEvent anywhere. Thus, once signalled, the event is remains set forever and WaitForSingleObject returns immediatelly. Make it an auto-reset event, or call ResetEvent after all workers are done.