?
Solved

Problems with threads.

Posted on 1999-01-21
6
Medium Priority
?
472 Views
Last Modified: 2013-11-20
Hello!
I have a multithreaded Client/Server. When clients are beginning to connect to this, the of all OS begins to work slow (immediately when I start new threads, the system works visible slower - after only two threads!!). The priority of threads is normal. The C-S communication is done through TCP/IP, using handles to CAsyncSocket derived classes, using WinSock API.
What is the problem??
Here is the looping code of the threads, which communicate with clients:

while (WaitForSingleObject(m_hEventKill, 0) == WAIT_TIMEOUT)
      {
            i =  recv( m_hSocket, b, 2, 0);
            if (i == 2)
            {
                    Do something.....
            }
            if (i == SOCKET_ERROR )
            {
                  switch (WSAGetLastError())
                  {
                  case WSAETIMEDOUT :
                  case WSAECONNRESET :
                  case WSAECONNABORTED :
                        {
                              m_theMessage = "@@##$$conerr";
                              ProcessPendingRead();
                              WaitForSingleObject(m_hEventKill, INFINITE);
                        }
                  }
            }
      };
0
Comment
Question by:tmolnar
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 4
  • 2
6 Comments
 

Author Comment

by:tmolnar
ID: 1328104
Edited text of question
0
 
LVL 4

Accepted Solution

by:
piano_boxer earned 200 total points
ID: 1328105
You are doing a BUSY wait because the timeout value for WaitForSingleObject is zero.

You can switch to using CAsyncSocket class the handles incomming data async. Derive your own class from CAsyncSocket and override OnReceive() and OnClose() functions.

OnReceive() will be called when there are some data ready to be read, and OnClose() will be called when the socket is closed.

You can add the derived CAsyncSocket class as a variable in you CWinApp and initialize it in OnInitInstance():

OnInitInstance(...)
{
   [...]
   m_MySocket.Create(12345, SOCK_STREAM, FD_READ|FD_CLOSE);
   [...]
}


Another solution is to use Winsock2 and use the WSAEventSelect function to enable signalling of a Win32 event when something happens on the socket.
0
 

Author Comment

by:tmolnar
ID: 1328106
If I do that, I have to cut out the will the
while (WaitForSingleObject(m_hEventKill, 0) == WAIT_TIMEOUT)
{
  ...
}
to avoid the busy wait...
But how to know, that the main thread want to kill the thread?
(see the m_hEventKill event)
Anoher question: the OnReceive() function will be called by the system, and will be work in the main thread on in the "client" thread?
Another problem is, that when I try to read in nonblocking mode all the time, I got an error, when the connection failed. How to get a corresponding error notification, if I use a CAsyncSocket derived class (something like On Error())?
0
Moving data to the cloud? Find out if you’re ready

Before moving to the cloud, it is important to carefully define your db needs, plan for the migration & understand prod. environment. This wp explains how to define what you need from a cloud provider, plan for the migration & what putting a cloud solution into practice entails.

 
LVL 4

Expert Comment

by:piano_boxer
ID: 1328107
I just re-read the question and there is really no need for you to use the thread function if you use the CAsyncSocket class.

Just drop the thread-thing for now.

The CAsyncSocket::OnReceive() function is call in the context of the thread that created the socket and is called by MFC through an internal hidden window MFC creates in CAsyncSocket::Create(). Windows posts socket event messages to this hidden windows and MFC calls the OnXxxx messages in response to them.

To read data from the socket do something like this in your OnReceive() overriden function:

void CMySocket::OnReceive(int nErrorCode)
{
    BYTE buf[512];
    CString strFromAddr;
    UINT nFromPort;

    int len = ReceiveFrom(buf, sizeof(buf), strFromAddr, nFromPort);
    if(len==0)
        // Connection closed !!!
    if(len>0)
    {
        // Use data in the buffer (buf).
    }
}

Here you also get the IP address and port of the sender. If you dont want this, just use the Receive() call instead.

Look at the nErrorCode passed to OnReceive() for errors.
0
 

Author Comment

by:tmolnar
ID: 1328108
Thax!! It's OK now...
0
 

Author Comment

by:tmolnar
ID: 1328109
Thanx!! It's OK now...
0

Featured Post

Will your db performance match your db growth?

In Percona’s white paper “Performance at Scale: Keeping Your Database on Its Toes,” we take a high-level approach to what you need to think about when planning for database scalability.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction: Ownerdraw of the grid button.  A singleton class implentation and usage. Continuing from the fifth article about sudoku.   Open the project in visual studio. Go to the class view – CGridButton should be visible as a class.  R…
In this post we will learn different types of Android Layout and some basics of an Android App.
This video will show you how to get GIT to work in Eclipse.   It will walk you through how to install the EGit plugin in eclipse and how to checkout an existing repository.
In this video you will find out how to export Office 365 mailboxes using the built in eDiscovery tool. Bear in mind that although this method might be useful in some cases, using PST files as Office 365 backup is troublesome in a long run (more on t…

777 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question