_Improving Server Performance_
by John Calcote

Listing One
/* Ping.cpp */

#define WIN32_EXTRA_LEAN
#include <windows.h>
#include <winsock.h>
#include <wsipx.h>
#include <conio.h>
#include "aes.h"

#define SERVER_SOCKET   0x3200

SOCKET g_skt;
BOOL g_serverUp;
AES *g_aesp;
AES::AESHandle g_hEvent;

void ServerThread(void *)
{
    if (!g_serverUp)
       return;
    fd_set rdSkts;
    FD_ZERO(&rdSkts);
    FD_SET(g_skt, &rdSkts);
    struct timeval tv = {5,0};
    int rval = select(0, &rdSkts, 0, 0, &tv);

    // schedule another pool thread to listen
    g_hEvent = g_aesp->ScheduleEvent(0, ServerThread, 0);

    // use this thread to process client request to completion
    if (rval < 0)
        printf("Winsock: select returned %d.\n", WSAGetLastError());
    else if (rval > 0)
    {
        SOCKADDR_IPX addr;
        int recvLen, addrLen = sizeof addr;
        char recvBuf[5];
        if ((recvLen = recvfrom(g_skt, recvBuf, sizeof recvBuf, 0,
            (struct sockaddr *)&addr, &addrLen)) == SOCKET_ERROR) 
        {
          printf("Winsock: recvfrom returned %d.\n",WSAGetLastError());
          return;
        }
        char *resp = strncmp(recvBuf,"Ping",5)?"101 Invalid Request.":"Pong";
        int respLen = strlen(resp) + 1;
        if (sendto(g_skt, resp, respLen, 0, (struct sockaddr *)&addr, 
                sizeof addr) == SOCKET_ERROR)
            printf("Winsock: sendto returned %d.\n", WSAGetLastError());
    }
    return;
}
BOOL StartServer(WORD wSocket) 
{
    int err;
    SOCKADDR_IPX addr;
    WSADATA wsaData;

    if (!(g_aesp = new AES))
    {
        printf("Unable to create AES object.\n");
        return FALSE;
    }
    if (err = WSAStartup(MAKEWORD(1,1), &wsaData))
    {
        printf("WSAStartup returned %d.\n", err);
        goto errout1;
    }
    if (LOBYTE(wsaData.wVersion) < 1 || HIBYTE(wsaData.wVersion) < 1)
    {
        printf("Winsock version too low.\n");
        goto errout2;
    }
    if ((g_skt = socket(AF_IPX, SOCK_DGRAM, NSPROTO_IPX)) == INVALID_SOCKET)
   {
        printf("Windsock: socket returned %d.\n", WSAGetLastError());
        goto errout2;
    }
    memset(&addr, 0, sizeof(SOCKADDR_IPX));
    addr.sa_family = AF_IPX;
    addr.sa_socket = htons(wSocket);
    if (bind(g_skt, (struct sockaddr *) &addr, sizeof(SOCKADDR_IPX)) != 0)
    {
        printf("Winsock: bind returned %d.\n", WSAGetLastError());
        goto errout3;
    }
    g_serverUp = TRUE;
    if (!(g_hEvent = g_aesp->ScheduleEvent(0, ServerThread, 0)))
    {
        printf("AES: Unable to schedule event.\n");
        g_serverUp = FALSE;
        goto errout3;
    }
    return TRUE;
errout3:
    closesocket(g_skt);
errout2:
    WSACleanup();
errout1:
    delete g_aesp;
    return FALSE;
}
void StopServer(void) 
{
    g_serverUp = FALSE;
    g_aesp->CancelEvent(g_hEvent);
    delete g_aesp;
    closesocket(g_skt);
    WSACleanup();
    return;
}
void main(void)
{
    if (StartServer(SERVER_SOCKET))
    {
        printf("Server running, press any key to terminate...\n");
        getch();
        StopServer();
    }
    printf("Server terminated, press any key to exit...\n");
    getch();
    return;
}

Listing Two
/* AES.cpp */

#include "AES.h"

#include <process.h>
#include <limits.h>
#include <crtdbg.h>

unsigned __stdcall AES::PoolThread::Worker(void *ref)
{
    PoolThread& This = *(PoolThread *)ref;
    while (!This.dying)
    {
        Event *event = This.event;
        This.event = 0;
        if (!event)
            WaitForSingleObject(This.sem, INFINITE);
        else
        {
            event->Work();
            delete event;
        }
    }
    return 0;
}
AES::PoolThread::PoolThread(int stack /* = 0 */ ) : dying(FALSE), 
        sem(0), handle(0), event(0), InitState(0) 
{
    if (!(sem = CreateSemaphore(0, 1, 0, 0))
            || !(handle = (HANDLE)_beginthreadex(0, stack, 
                    Worker, 0, 0, 0)))
        InitState = ERR_CANT_CREATE_HANDLE;
    return;
}
AES::PoolThread::~PoolThread(void)
{
    dying = TRUE;
    if (sem)
    {
        if (handle)
        {
            ReleaseSemaphore(sem, 1, 0);
            WaitForSingleObject(handle, INFINITE);
            CloseHandle(handle);
        }
        CloseHandle(sem);
    }
    return;
}
unsigned __stdcall AES::Monitor(void *ref)
{
   AES &This = *(AES*)ref;
    _CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_DEBUG);
    while (!This.dying)
    {
        int eventsWaiting = 0;
        ULONG now = ULONG(clock() / CLOCKS_PER_SEC);
        ULONG nextEventTime = ULONG_MAX, lastComplaintTime = 0;
        EnterCriticalSection(&This.critSec);
        for (EventList::iterator eli = This.eventList.begin(); 
                eli != This.eventList.end(); /**/ )
        {
            for (int i = 0; i < This.size && This.pool[i].Busy(); i++)
                ;   // find next available worker
            if (i < This.size && (*eli)->When() <= now)
            {
                Event *event = *eli;
                eli = This.eventList.erase(eli);
                This.pool[i].Alloc(event);
            }
            else
            {
                if ((*eli)->When() <= now)
                    eventsWaiting++;
                else if ((*eli)->When() < nextEventTime)
                    nextEventTime = (*eli)->When();
                eli++;
            }
        }
        LeaveCriticalSection(&This.critSec);
        if (!eventsWaiting)
            WaitForSingleObject(This.sem, (nextEventTime - now) * 1000);
        else
        {
            if (lastComplaintTime + 3 < now)
            {
                _CrtDbgReport(_CRT_WARN, 0, 0, 0,
                    "Thread pool overflow. %d events delayed.", eventsWaiting);
                lastComplaintTime = now;
            }
            Sleep(100);
        }
    }
    return 0;
}
AES::AESHandle AES::ScheduleEvent(ULONG ulDelay, 
                                           void (*pFunc)(void*), void *pData)
{
    Event *event;
    _ASSERT(pFunc);
    if (!(event = new Event(ulDelay, pFunc, pData)))
       return AESHandle(0);
    EnterCriticalSection(&critSec);
    eventList.push_front(event);
    LeaveCriticalSection(&critSec);
    ReleaseSemaphore(sem, 1, 0);
    return AESHandle(event);
}
BOOL AES::CancelEvent(AESHandle hEvent)
{
    Event *event = (Event *)hEvent;
    BOOL cancelled = FALSE;
    EnterCriticalSection(&critSec);
    for (EventList::iterator eli = eventList.begin(); 
            eli != eventList.end(); eli++)
        if (*eli == event)
        {
            eventList.erase(eli);
            delete event;
            cancelled = TRUE;
            break;
        }
    LeaveCriticalSection(&critSec);
    return cancelled;
}
AES::AES(int threads /* = 10 */) : dying(FALSE), sem(0), 
        handle(0), size(threads), pool(0), InitState(0)
{
    // Initialize event list critical section 
    InitializeCriticalSection(&critSec);
    // Allocate thread pool
    if (!(pool = new PoolThread[size]))
    {
        InitState = ERR_INSUFFICIENT_MEMORY;
        return;
    }
    // Check init state of threads in pool
    for (int i = 0; i < size; i++)
        if (pool[i].InitState)
        {
            InitState = pool[i].InitState;
            return;
        }
    // Create monitor semaphore and thread
    if (!(sem = CreateSemaphore(0, 0, 1, 0))
            || !(handle = (HANDLE)_beginthreadex(0, 0, Monitor, this, 0, 0)))
        InitState = ERR_CANT_CREATE_HANDLE;
   return;
}
AES::~AES(void)
{
    dying = TRUE;
    if (sem)
    {
        if (handle)
        {
            ReleaseSemaphore(sem, 1, 0);
            WaitForSingleObject(handle, INFINITE);
            CloseHandle(handle);
        }
        CloseHandle(sem);
    }
    delete [] pool;
    DeleteCriticalSection(&critSec);
    return;
}