IOCP Server - VB6

The attached server program is my nextt attempt at using IOCP {Input Output Completion Port). It is based on one submitted by xiaoyao, but I am not sure who deserves the credit as it was a repost.

To be effective at fully serving the needs of a high usage server, IOCP needs to be used in Overlapped mode as well as Multi Threaded mode. Overlapped I/O in non-blocking or asynchronous mode using multiple threads based on the number of CPU cores available, delivers the highest throughput according to Microsoft. My own experience so far supports that. Unfortunately there is very little information out there on utilizing this function with VB6. What I could find was information about C++ and .NET implementations with echo servers, and this information was not very helpful. Stepping through the program to identify problems proved to be next to impossible without the IDE crashing, so I was left with a lot of trial and error solutions to fix bugs.

Although this program is currently designed to use non-encrypted data, the intention is to eventually add encryption. To this end the first transmission after connecting to the server is a simple Client Hello ("Hello") using a 5 byte header. Overlapped I/O apparently has the ability to split the data into separate buffers (eg. Header/Body), but I have not yet attempted to implement that.

Overlapped I/O uses a fixed length buffer along with a length variable. Therefore it is not necessary to clear the buffer on each pass. The size of that buffer is configurable, and should be adjusted to suit the application. An application that hosts many connections with relatively short messages should have a smaller buffer than one that exchanges larger messages. This has to be balanced against operations such as encryption. Longer buffers take more processor power than shorter buffers. For this particular application, I have chosen 8,192 bytes as a starting point.

When a request is passed to a thread with a WSARecv or WSASend, the request is directed to the appropriate thread defined by ComKey, which is the Completion Key being used as the index to the connection array.

Sending encrypted files over a network requires messages to be sent as data defined by a header that can be decrypted as a complete block of data as defined in:
https://www.vbforums.com/showthread....13-VB6-GetFile

This worked well until I started experimenting with high speed server traffic over a Local Area network using IOCP in the IDE. File transfers must store the file blocks as they are received and decrypted to avoid having to store the entire file in memory before storage. Normally, network speed is slower than program speed, but in this scenario, the opening of the file for download was slow enough to only save the first record. Subsequently I have implemented an option to open the file in the client prior to starting the download.

Because much of the work is done by the API, the code is relatively short in comparison to my previous attempts at server networking. The downside is that it is also less flexible. The same buffer is used for sending as receiving. We signal the buffer to receive data by applying a "WSARecv". An endless loop in the worker thread detects incoming traffic with GetQueuedCompletionStatus (GQCS), the index for the connection is recovered, and the recovered bytes are made available. Whether or not the buffer is returned before it is complete is unknown at this time. To change from receiving to sending, we apply a "WSASend" with the bytes to be sent in "PerData(nPerIndex).Buf" and the number of bytes in "PerData(nPerIndex).Len". This program currently does not support IPv6.

That's about the gist of it, with some changes to file I/O. Using File API, I was able to improve speed and provide for automatic detection of file existence and prompting the operator before overwriting.

There will probably be some bugs to fix. Feedback is welcome.

J.A. Coutts

Note: IOCP_Svr.zip & GetFile.zip have been restored. See post #15 for details
Update: GetFile has been updated. See post #26 for details
Update: (8/16/2024) IOCP_Svr has been updated. See post #30 for details
Update: (01/25/2025) See post #33 for details
Update: (11/15/2025) See post #44 for details
Update: (01/23/2026) See post #45 for details

A problem has already surfaced. When I compile the server program and attempt to run it, it crashes after initialization. I could really use some help with this one, because my experience with Multi Threading is very limited.

J.A. Coutts

Use this module for threading.

Quote:

---

Originally Posted by The trick

Use this module for threading.

---

I commend you for the work you have done on multi threading in VB6, but in this particular instance that module is far more than what I need. The threads do not have to communicate with each other or any other controls, and do not need to be marshalled. I simply need to make them work fast and efficiently when compiled.

J.A. Coutts

Quote:

---

Originally Posted by couttsj

I commend you for the work you have done on multi threading in VB6, but in this particular instance that module is far more than what I need. The threads do not have to communicate with each other or any other controls, and do not need to be marshalled. I simply need to make them work fast and efficiently when compiled.

J.A. Coutts

---

Okay, then don't be surprised when you get crashes ;) The module provides "flat" threads as well when you use vbCreateThread.

Quote:

---

Originally Posted by couttsj

I simply need to make them work fast and efficiently when compiled.

---

The point is that first you have to make them *work at all* when compiled.

cheers,
</wqw>

Quote:

---

Originally Posted by The trick

Okay, then don't be surprised when you get crashes ;) The module provides "flat" threads as well when you use vbCreateThread.

---

Well, you are right. After more research, the standard EXE that VB6 produces apparently marshals all the threads into one. The ActiveX EXE does not. Also, I checked the IDE version to see if all the threads were being used, and they are. But the IDE crashes when I attempt to transfer multiple records over anything but the first connection.

How does one tell if more than one CPU core is being used?

J.A. Coutts

It's better to make an AxDll (apartment threading) and create an object for each IOCP thread. I wouldn't recommend to use Std-EXE threading because you lose the debugging ability (each IOCP thread sleeps in most time). Of course you could use a small asm thunk (the cycle with GetQueuedCompletionStatus call) to transmit the data from an IOCP thread to the main thread using my module as well. Regarding to AxDll approach, i had the experience with such approach when i needed to run several instances of ActiveScripting engines simultaneously:

Code:

---

Public Function ThreadProc( _
                ByRef tData As tThreadData) As Long
    Dim hWnd    As Long
    Dim tMsg    As MSG
    Dim lRet    As Long
    Dim pObj    As Long
   
    If tData.hr < 0 Then Exit Function
   
    hWnd = tData.hWnd
    pObj = tData.pObjectRaw
   
    Do
   
        lRet = GetMessage(tMsg, 0, 0, 0)
       
        If lRet = -1 Then
            ' // Error
            tData.hr = E_FAIL
            Exit Do
        ElseIf lRet = 0 Then
            ' // Exit message queue
            Exit Do
        Else
            TranslateMessage tMsg
            DispatchMessage tMsg
        End If
       
    Loop While True
       
    If tData.pObjectRaw Then
        vbaObjSetAddref pObj, ByVal 0&
    End If
       
End Function

Public Function ThreadInitProc( _
                ByRef tData As tThreadData) As Long
    Dim hr      As Long
    Dim tClsId  As UUID
   
    ' // Create communication window
    tData.hWnd = CreateWindowEx(0, THREAD_WND_CLASS, vbNullString, 0, 0, 0, 0, 0, HWND_MESSAGE, 0, tData.hInstance, ByVal 0&)
   
    If tData.hWnd = 0 Then
        hr = E_FAIL
        GoTo exit_proc
    End If
   
    tData.lThreadID = GetCurrentThreadId()
    tData.hThread = OpenThread(SYNCHRONIZE, 0, tData.lThreadID)
   
    hr = CLSIDFromProgID(tData.sProgID, tClsId)
    If hr < 0 Then GoTo exit_proc
   
    ' // Create object
    hr = CoCreateInstance(tClsId, Nothing, CLSCTX_INPROC_SERVER, IID_IUnknown, tData.pObjectRaw)
    If hr < 0 Then GoTo exit_proc
   
    ' // Marshal
    hr = CoMarshalInterThreadInterfaceInStream(tData.tIID, ByVal tData.pObjectRaw, tData.pStream)
    If hr < 0 Then GoTo exit_proc
   
    tData.bInitialized = True
   
exit_proc:
   
    If hr < 0 Then
       
        If tData.pStream Then
            vbaObjSetAddref tData.pStream, ByVal 0&
        End If
       
        If tData.hThread Then
            CloseHandle tData.hThread
            tData.hThread = 0
        End If
       
        If tData.lThreadID Then
            tData.lThreadID = 0
        End If
       
        If tData.pObjectRaw Then
            vbaObjSetAddref tData.pObjectRaw, ByVal 0&
        End If
       
        tData.bInitialized = False
       
        If tData.hWnd Then
            DestroyWindow tData.hWnd
            tData.hWnd = 0
        End If
       
    End If
   
    tData.hr = hr
   
End Function


...

Public Sub CreateObjectInThread( _
          ByRef sProgID As String)
    Dim hr      As Long
    Dim cObj    As Object
   
    If m_tThreadData.hThread Then
        Err.Raise 5, "CThreadItem::CreateObjectInThread", "There is an active object in the thread"
    End If

    With m_tThreadData
   
        .sProgID = sProgID
        .tIID = IID_IDispatch
        .hInstance = App.hInstance
        .hr = 0
        .hThread = 0
        .hWnd = 0
        .lThreadID = 0
        .pObjectRaw = 0
        .pStream = 0

    End With
   
    hr = SHCreateThread(AddressOf ThreadProc, m_tThreadData, CTF_COINIT_STA, AddressOf ThreadInitProc)
    If hr < 0 Then Err.Raise hr
   
    If m_tThreadData.hr Then Err.Raise m_tThreadData.hr
   
    hr = CoGetInterfaceAndReleaseStream(ByVal m_tThreadData.pStream, IID_IDispatch, cObj)
   
    If hr < 0 Then Err.Raise hr
   
    Set m_cObjInThread = cObj
   
End Sub

---

I have made a little progress with this application. I discovered that when a thread is created, it is executed immediately, and that presented timing issues. Setting up the listening socket does not require that code to be part of the listening thread, so it was moved outside of the thread code.

In the IDE, it was discovered that only the first working thread was created. Using a brief delay (Sleep 10) in the working thread initialization loop solved that problem, and coincidently it solved the same issue in the executable. The executable would crash after initializing the first working thread, and now it crashes after initializing all the working threads.

Experimenting with the executable, it would remain running if I did not initialize the working threads. So I enabled the working thread initialization routine, but commented out the bulk of the code within the routine. Low and behold, the executable stayed running. So the problem in the executable seems to be related to the size of the code. I am finding it difficult to merge IOCP with any existing VB thread code, as IOCP already handles much of it.

J.A. Coutts

If handled well, multithreading won't crash when compiled into an exe. Is your crash problem solved now?

Quote:

---

Originally Posted by The trick

It's better to make an AxDll (apartment threading) and create an object for each IOCP thread. I wouldn't recommend to use Std-EXE threading because you lose the debugging ability (each IOCP thread sleeps in most time). Of course you could use a small asm thunk (the cycle with GetQueuedCompletionStatus call) to transmit the data from an IOCP thread to the main thread using my module as well. Regarding to AxDll approach, i had the experience with such approach when i needed to run several instances of ActiveScripting engines simultaneously:

Code:

---

Public Function ThreadProc( _
                ByRef tData As tThreadData) As Long
    Dim hWnd    As Long
    Dim tMsg    As MSG
    Dim lRet    As Long
    Dim pObj    As Long
   
    If tData.hr < 0 Then Exit Function
   
    hWnd = tData.hWnd
    pObj = tData.pObjectRaw
   
    Do
   
        lRet = GetMessage(tMsg, 0, 0, 0)
       
        If lRet = -1 Then
            ' // Error
            tData.hr = E_FAIL
            Exit Do
        ElseIf lRet = 0 Then
            ' // Exit message queue
            Exit Do
        Else
            TranslateMessage tMsg
            DispatchMessage tMsg
        End If
       
    Loop While True
       
    If tData.pObjectRaw Then
        vbaObjSetAddref pObj, ByVal 0&
    End If
       
End Function

Public Function ThreadInitProc( _
                ByRef tData As tThreadData) As Long
    Dim hr      As Long
    Dim tClsId  As UUID
   
    ' // Create communication window
    tData.hWnd = CreateWindowEx(0, THREAD_WND_CLASS, vbNullString, 0, 0, 0, 0, 0, HWND_MESSAGE, 0, tData.hInstance, ByVal 0&)
   
    If tData.hWnd = 0 Then
        hr = E_FAIL
        GoTo exit_proc
    End If
   
    tData.lThreadID = GetCurrentThreadId()
    tData.hThread = OpenThread(SYNCHRONIZE, 0, tData.lThreadID)
   
    hr = CLSIDFromProgID(tData.sProgID, tClsId)
    If hr < 0 Then GoTo exit_proc
   
    ' // Create object
    hr = CoCreateInstance(tClsId, Nothing, CLSCTX_INPROC_SERVER, IID_IUnknown, tData.pObjectRaw)
    If hr < 0 Then GoTo exit_proc
   
    ' // Marshal
    hr = CoMarshalInterThreadInterfaceInStream(tData.tIID, ByVal tData.pObjectRaw, tData.pStream)
    If hr < 0 Then GoTo exit_proc
   
    tData.bInitialized = True
   
exit_proc:
   
    If hr < 0 Then
       
        If tData.pStream Then
            vbaObjSetAddref tData.pStream, ByVal 0&
        End If
       
        If tData.hThread Then
            CloseHandle tData.hThread
            tData.hThread = 0
        End If
       
        If tData.lThreadID Then
            tData.lThreadID = 0
        End If
       
        If tData.pObjectRaw Then
            vbaObjSetAddref tData.pObjectRaw, ByVal 0&
        End If
       
        tData.bInitialized = False
       
        If tData.hWnd Then
            DestroyWindow tData.hWnd
            tData.hWnd = 0
        End If
       
    End If
   
    tData.hr = hr
   
End Function


...

Public Sub CreateObjectInThread( _
          ByRef sProgID As String)
    Dim hr      As Long
    Dim cObj    As Object
   
    If m_tThreadData.hThread Then
        Err.Raise 5, "CThreadItem::CreateObjectInThread", "There is an active object in the thread"
    End If

    With m_tThreadData
   
        .sProgID = sProgID
        .tIID = IID_IDispatch
        .hInstance = App.hInstance
        .hr = 0
        .hThread = 0
        .hWnd = 0
        .lThreadID = 0
        .pObjectRaw = 0
        .pStream = 0

    End With
   
    hr = SHCreateThread(AddressOf ThreadProc, m_tThreadData, CTF_COINIT_STA, AddressOf ThreadInitProc)
    If hr < 0 Then Err.Raise hr
   
    If m_tThreadData.hr Then Err.Raise m_tThreadData.hr
   
    hr = CoGetInterfaceAndReleaseStream(ByVal m_tThreadData.pStream, IID_IDispatch, cObj)
   
    If hr < 0 Then Err.Raise hr
   
    Set m_cObjInThread = cObj
   
End Sub

---

---

when i needed to run several instances of ActiveScripting engines simultaneously:
Is there a test project for this? Thank you

SHCreateThread
vbaObjSetAddref

' // Marshal
hr = CoMarshalInterThreadInterfaceInStream(tData.tIID,
CoGetInterfaceAndReleaseStream(ByVal
Can you talk about why you use these APIs? I've never used these things before.

The reason for developing this program is that on larger file transfers, the Client program I was using (built with SimpleSock), was not fast enough to keep up with the IOCP server program I was working on, when both programs were operating in the IDE. I wanted to NOT use multithreading on the Client program, but I could not find a way to leave the endless loop in a signaled state without using the API function "CreateThread". So I ended up with a single threaded Client program instead.

Each record is preceded by a 5 byte header, containing the record Type, the 2 byte version, and the 2 byte record length.
To summarize the program flow:
- Initialize working thread.
- Connect to server port (5150).
- Send Client Hello (Type 1).
- Server responds with a list of available files and length (Type 8).
- Client adds these to the listBox.
- Client clicks on desired file, sends it to the server (Type 8), and opens the file for receipt.
- Server opens that file and starts sending in blocks of 8192 bytes (Type 9).
- Client receives each block, adds it to the file and decrements the file length.
- When the file length is less than or equal to the "BlockLen", the file is closed and the operation is complete.

All this worked quite nicely while operating in the IDE. But when I compiled the program and ran it, it crashed as soon as it attempted to save the file. A zero length file would be left open. I suspected that the problem might be a conflict between IOCP and the VB6 file system. That is why I experimented with the Windows file API (See: https://www.vbforums.com/showthread....ndows-File-API ). That appears to be a good guess, because when I changed the program to use the API, the executable crash problem went away.

For testing purposes, I have provided a server program that uses SimpleSock. It was easy to throw together, and SimpleSock is quite stable, but also quite slow. If you are going to use this program in the IDE for files more than a few records, be sure to disable some of the Debug.Print statements, as the Immediate window has very limited capacity.

This is a work in progress, as is the IOCP server program. To implement IOCP in this Client program, I used a single structure to define the server, but I retained the structure array for the Client in case I wanted to allow it to support more than one download at a time. I have temporarily removed the IOCP server program as I try to resolve some of the issues in that particular program.

J.A. Coutts

Some Chinese have achieved iocp server for webserver,websocket
the goal of supporting 100,000 concurrency without crashing.
You definitely need to use multithreading.

Quote:

---

Originally Posted by xiaoyao

Some Chinese have achieved iocp server for webserver,websocket
the goal of supporting 100,000 concurrency without crashing.
You definitely need to use multithreading.

---

The need for multi threading on the Client end is highly questionable considering the amount of resources it requires. On the Server end however, it is very desirable.

J.A. Coutts

In this latest update, the IOCP Server essentially remains the same, but with some improvements in the File I/O. GetFile is still using SimpleSock with a much improved File I/O. If the file to be downloaded already exists and the API uses the "OPEN_ALWAYS" option, the API opens the file but returns "ERROR_ALREADY_EXISTS". Should the operator choose to overwrite the file, the file is closed and reopened using the "TRUNCATE_EXISTING" option. This is similar to the way the Command Line uses the Copy command.

If anyone can provide a better work around for the Start delays, I am all ears. Without fully understanding exactly how VB6 works, I can only guess that the problem is that the call automatically initiates the thread process, which can take longer than the API call itself depending on its size. The current process appears to be quite stable in the IDE as well as compiled.

J.A. Coutts

Maybe it can be packaged as a WEBSOCKET purpose?

Code:

---

Sub WaitEventAnsy(ByVal hEvent As Long)  '
    Do While MsgWaitForMultipleObjects(1&, hEvent, 0&, INFINITE, QS_ALLINPUT)  '??1??0????
        DoEvents
    Loop
 
End Sub

---

Code:

---

Sub WaitEventByFrm(frm As Form)
 Dim hEvent As Long
    hEvent = CreateEvent(ByVal 0, 1, 0, vbNullString)  '"Event" & f2.hwnd
   
    frm.EventHandle = hEvent
   
    WaitEventAnsy hEvent
    Do While MsgWaitForMultipleObjects(1&, hEvent, 0&, INFINITE, QS_ALLINPUT)  '??1??0????
        DoEvents
    Loop
        CloseHandle hEvent
End Sub

---

Code:

---

form1.frm

Public EventHandle As Long
Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer)

If EventHandle <> 0 Then SetEvent EventHandle
End Sub

---

Vb6 sends and receives event signals across processes, CreateEvent.

Code:

---

Dim Start As Date
Private Declare Function ResetEvent Lib "kernel32" (ByVal hEvent As Long) As Long
Private Declare Function CreateEvent Lib "kernel32" Alias "CreateEventA" (lpEventAttributes As Any, ByVal bManualReset As Long, ByVal bInitialState As Long, ByVal lpName As String) As Long
Private Declare Function SetEvent Lib "kernel32" (ByVal hEvent As Long) As Long
Private Declare Function OpenEvent Lib "kernel32.dll" Alias "OpenEventA" ( _
                                        ByVal dwDesiredAccess As Long, _
                                        ByVal bInheritHandle As Long, _
                                        ByVal lpName As String) As Long
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long

Private Const STANDARD_RIGHTS_REQUIRED As Long = &HF0000
Private Const SYNCHRONIZE As Long = &H100000
Private Const EVENT_ALL_ACCESS As Long = (STANDARD_RIGHTS_REQUIRED Or SYNCHRONIZE Or &H3)

Private Const INFINITE As Long = -1&
Private Const QS_ALLINPUT As Long = &H4FF&
Private Declare Function MsgWaitForMultipleObjects Lib "user32.dll" (ByVal nCount As Long, ByRef pHandles As Long, ByVal bWaitAll As Long, ByVal dwMilliseconds As Long, ByVal dwWakeMask As Long) As Long
 
 Dim hEvent As Long

Private Sub Command1_Click()
'From ABC.EXE WaitEvent:
Command1.Enabled = False
Start = Now

    'hEvent = CreateEvent(ByVal 0, 1, 0, "eventName1")
    hEvent = CreateEvent(0&, False, False, "eventName1")
WaitEventAnsy hEvent
Me.Caption = "WaitEvent:" & DateDiff("s", Start, Now) & "?"
Command1.Enabled = True
End Sub

sub WaitMessageAgain
    ResetEvent  hEvent
    WaitEventAnsy hEvent
end sub

Private Sub Command2_Click()
'From Client2.exe 'SetEvent,So ABC.EXE Will Get Event Message

    hEvent = OpenEvent(EVENT_ALL_ACCESS, False, "eventName1")

    If hEvent <> 0 Then
    SetEvent hEvent
    Else
    MsgBox "hEvent=0"
    End If
End Sub

Sub WaitEventAnsy(ByVal hEvent As Long)  '
    Do While MsgWaitForMultipleObjects(1&, hEvent, 0&, INFINITE, QS_ALLINPUT)  '??1??0????
        DoEvents
    Loop

End Sub

Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer)
    CloseHandle hEvent
End
End Sub

---

Quote:

---

Originally Posted by xiaoyao

Vb6 sends and receives event signals across processes, CreateEvent.

---

Sorry, but I do not understand the connection between the CreateThread difficulty and CreateEvent.

J.A. Coutts

Quote:

---

Originally Posted by couttsj

Sorry, but I do not understand the connection between the CreateThread difficulty and CreateEvent.

J.A. Coutts

---

. I wanted to NOT use multithreading on the Client program, but I could not find a way to leave the endless loop in a signaled state without using the API function "CreateThread". So I ended up with a single threaded Client program instead.

I don't know exactly what function you want to do.
Why use multithreading? What are you waiting for?

Quote:

---

Originally Posted by xiaoyao

. I wanted to NOT use multithreading on the Client program, but I could not find a way to leave the endless loop in a signaled state without using the API function "CreateThread". So I ended up with a single threaded Client program instead.

I don't know exactly what function you want to do.
Why use multithreading? What are you waiting for?

---

The single threaded Client program is still in development and is not part of the current download.

Threads are used to facilitate speedy network transmission using IOCP, fixed length records, and the actual length transmitted via the record header. When a thread is initialized, it has to allocate memory and load the thread process, leaving it in the signalled state using WSARecv to receive incoming data. When sending data, the data is loaded into the buffer before enabling the signalled state using WSASend.

To setup each thread, CreateThread is used to run GetQueuedCompletionStatus (sometimes called GQCS). This is called the signalled state, as it remains in that state until it receives a signal that an I/O function has completed, whereupon it processes that I/O and waits for the next instruction.

According to Microsoft, CreateThread can return before the thread has been enabled. In order to not crash using VB6, each thread is given 500 ms to finish loading accompanied by a form print to indicate that it is loaded and ready. This combination was discovered by trial and error, and why it works is unknown to me. Without it the program crashes, both compiled and in the IDE.

J.A. Coutts

You can create 10 thread and suspend them if you complete the task.When the main program receives a new request, it wakes up and lets it continue to process the task.You can also send him a task instruction to call a different process.

It can also turn all the tasks to be processed into a sequence. Processed sequentially by each multithread.

I finally got a single thread IOCP to receive a file without crashing, and the results were pretty much what I expected.
-------------------------------------
transfer 64 KB file over local network
(File Open & File Close not included)

Using SimpleSock for send and receive:
110ms transfer complete!

Using SimpleSock for send and IOCP for receive:
124ms transfer complete!

Using IOCP for send and SimpleSock for receive:
32ms transfer complete!

Using IOCP for send and IOCP for receive:
doesn't complete transfer (2 records only)
--------------------------------------
The only conclusion I can come to is that using IOCP to receive files simply isn't worth the effort, but using IOCP to send files certainly is. One other thing that I noticed was that File Close seems to take quite a long time using IOCP for receiving. That is probably not significant if multiple threads were used.

J.A. Coutts

How can a piece of software support 100,000 user connections? This is when multithreading is important.

Quote:

---

Originally Posted by xiaoyao

How can a piece of software support 100,000 user connections? This is when multithreading is important.

---

100,000 user connections does not mean 100,000 active users. Each thread can only service 1 connection at a time, but a single thread can be made to support more than 1 connection in series. Further more the maximum number of TCP ports is 65,536. To achieve 100,000 connections, other facilities are necessary such as a server farm.

J.A. Coutts

A bug was discovered in the GetFile program that did not save the last record. Not sure why, but the JPEG files I was testing with displayed properly without that last record.

After correcting that flaw and fixing up a few other things, the 64KB file transferred in a time of 16ms. When both programs were run compiled, the results were the same. That simply demonstrates that the limiting factor is network speed. By way of comparison, transferring a 1,608KB file took 328ms, and a 10.7GB file took 1,705ms. These are all timed when overwriting existing files, and does not account for file buffering. For example, the 10.7GB file took 2,578ms after deleting the existing file and rebooting the client computer.

Many of the debug statements in this version of GetFile have been commented out. If you are going to transfer relatively large files with IOCP_Svr in the IDE, it is advisable to comment out some of the debug statements there as well. The immediate window in the IDE has limited capacity, and too many debug prints will cause problems.

J.A. Coutts

Quote:

---

Originally Posted by couttsj

The attached server program is my first attempt at using IOCP {Input Output Completion Port). It is based on one submitted by xiaoyao, but I am not sure who deserves the credit as it was a repost.

To be effective at fully serving the needs of a high usage server, IOCP needs to be used in Overlapped mode as well as Multi Threaded mode. Overlapped I/O in non-blocking or asynchronous mode using multiple threads based on the number of CPU cores available, delivers the highest throughput according to Microsoft. My own experience so far supports that. Unfortunately there is very little information out there on utilizing this function with VB6. What I could find was information about C++ and .NET implementations with echo servers, and this information was not very helpful. Stepping through the program to identify problems proved to be next to impossible without the IDE crashing, so I was left with a lot of trial and error solutions to fix bugs.

Although this program is currently designed to use non-encrypted data, the intention is to eventually add encryption. To this end the first transmission after connecting to the server is a simple Client Hello ("Hello") using a 5 byte header. Overlapped I/O apparently has the ability to split the data into separate buffers (eg. Header/Body), but I have not yet attempted to implement that.

Overlapped I/O uses a fixed length buffer along with a length variable. Therefore it is not necessary to clear the buffer on each pass. The size of that buffer is configurable, and should be adjusted to suit the application. An application that hosts many connections with relatively short messages should have a smaller buffer than one that exchanges larger messages. This has to be balanced against operations such as encryption. Longer buffers take more processor power than shorter buffers. For this particular application, I have chosen 8,192 bytes as a starting point.

When a request is passed to a thread with a WSARecv or WSASend, the request is directed to the appropriate thread defined by ComKey, which is the Completion Key being used as the index to the connection array.

Sending encrypted files over a network requires messages to be sent as data defined by a header that can be decrypted as a complete block of data as defined in:
https://www.vbforums.com/showthread....13-VB6-GetFile

This worked well until I started experimenting with high speed server traffic over a Local Area network using IOCP in the IDE. File transfers must store the file blocks as they are received and decrypted to avoid having to store the entire file in memory before storage. Normally, network speed is slower than program speed, but in this scenario, the opening of the file for download was slow enough to only save the first record. Subsequently I have implemented an option to open the file in the client prior to starting the download.

Because much of the work is done by the API, the code is relatively short in comparison to my previous attempts at server networking. The downside is that it is also less flexible. The same buffer is used for sending as receiving. We signal the buffer to receive data by applying a "WSARecv". An endless loop in the worker thread detects incoming traffic with GetQueuedCompletionStatus (GQCS), the index for the connection is recovered, and the recovered bytes are made available. Whether or not the buffer is returned before it is complete is unknown at this time. To change from receiving to sending, we apply a "WSASend" with the bytes to be sent in "PerData(nPerIndex).Buf" and the number of bytes in "PerData(nPerIndex).Len". This program currently does not support IPv6.

That's about the gist of it, with some changes to file I/O. Using File API, I was able to improve speed and provide for automatic detection of file existence and prompting the operator before overwriting.

There will probably be some bugs to fix. Feedback is welcome.

J.A. Coutts

Note: IOCP_Svr.zip & GetFile.zip have been restored. See post #15 for details
Update: GetFile has been updated. See post #26 for details

---

The link I originally sent should also be posted.
The website I originally downloaded from has been closed.
Like our vbforums community, 90% of the sites that survive purely on advertising have been shut down.So a little advertising fee can not maintain the server of the website and the cost of maintenance.

Quote:

---

Originally Posted by xiaoyao

The link I originally sent should also be posted.
The website I originally downloaded from has been closed.
Like our vbforums community, 90% of the sites that survive purely on advertising have been shut down.So a little advertising fee can not maintain the server of the website and the cost of maintenance.

---

I gave yourself credit even though your original post was a repost of someone else's work. Unfortunately, that post and any other postings I could find were of very limited value because they were all about Echo Servers. What I have finally come up with bears little resemblance to an Echo Server.

J.A. Coutts

Ran into a problem when exiting the server program in the IDE after transferring a large file (10.7 GB). The IDE itself would crash. The only function that operates upon exiting the program is shutting down the threads. For that I was using TerminateThread. MS cautions about using TerminateThread from outside of the thread itself, stating "If the target thread is allocating memory from the heap, the heap lock will not be released".

The normal way of starting and stopping threads is to create an event and pick up the event code using WaitForSingleObject. But the threads using IOCP are not stopped and started like normal threads. The threads are put into a signaled state and simply sit there waiting for a signal to start processing a single buffer. Once processed they are programmed to enter the signaled state again. All this is complicated by the fact that VB handles much of the cleanup itself without requiring program intervention.

So I started searching for answers. One response in StackOverflow suggested:
--------------------------------------------------
Safe options to kill a thread and exit could be:
TerminateThread(thd);
__fastfail(0);
or
TerminateThread(thd);
TerminateProcess(GetCurrentProcess(), 0);
--------------------------------------------------
I could not find any info on using "fastFail" with VB, and a number of posts advised against it. So it was back to the old Trial and Error method again. What I found was that TerminateProcess alone solved the problem. From that I assume that TerminateThread simply kills the thread without doing any cleanup, whereas TerminateProcess (or VB6 itself) does some cleanup before killing the thread.

Public Declare Function TerminateProcess Lib "kernel32" (ByVal hProcess As Long, ByVal uExitCode As Long) As Long

J.A. Coutts
Note: The download has not been updated yet.


Addendum:
Terminating a process has the following results:
Any remaining threads in the process are marked for termination.
Any resources allocated by the process are freed.
All kernel objects are closed.
The process code is removed from memory.
The process exit code is set.
The process object is signaled.

A bug in IOCP_Svr was discovered that went undetected. When the file length was less than the maximum record size (BlockLen), the server would send 2 copies of the file. GetFile did not complain, and it is presumed that it saved the file twice.

The thread generation and termination routines were moved to the module along with updating TerminateThread to TerminateProcess. As well, a system call recovers the number of CPU processors and generates a thread for each one up to a maximum of 8.

J.A. Coutts

If the task of a thread has been completed, it can be suspended directly.When you have a task, you can choose which free trips to let him recover.

Quote:

---

Originally Posted by xiaoyao

If the task of a thread has been completed, it can be suspended directly.When you have a task, you can choose which free trips to let him recover.

---

IOCP threads are never completed until the program is ended. After one task is completed, that particular connection is theoretically suspended. It has to be told what to expect for the next task (WSARecv or WSASend). It has no idea when that will occur, so it should be immediately assigned a task. In the meantime that thread can service any other connections it has been assigned. If zero bytes are recovered, it is because the other end closed the socket, and our end should do the same.

So you can see that we are never completely in charge of what the thread is doing. We cannot arbitrarily stop and start the thread.

J.A. Coutts

When IOCP_Svr was run on a Windows 8.1 machine with 4 processors, it ran without a problem until the server was shut down, at which point the IDE would crash. This would not occur on the Windows 11 machine with 8 processors.

I noticed that did not occur if I stepped through the termination process, so I added a brief delay between terminating each thread. This appears to have corrected the problem.

J.A. Coutts

Quote:

---

Originally Posted by couttsj

When IOCP_Svr was run on a Windows 8.1 machine with 4 processors, it ran without a problem until the server was shut down, at which point the IDE would crash. This would not occur on the Windows 11 machine with 8 processors.

I noticed that did not occur if I stepped through the termination process, so I added a brief delay between terminating each thread. This appears to have corrected the problem.

J.A. Coutts

---

vb6 ide,Will it crash when parsing and executing?
It would be nice to be able to resolve the run inside idE so that it can safely exit multithreading.

I tried some code once. I launched five multi-threaded requests at once. The IDE crashes.
Slow down when creating multiple threads. For example, click two buttons to create two multithreads, and then execute the task for five minutes. So it doesn't fall apart.
The normal operation of multithreading automatically exits, and sometimes closing the form will not crash.

But re-run it a few times and it will crash.

These problems can only be found by looking at assembly or debugging.

At present, no one has been able to solve the problem of crash in the VB6 IDE.

createthread addressof test
sib test()
sleep 10000
end sub

I've tried it many times, and sometimes I can run it several times in a row without crashing, and sometimes it crashes again.
I don't know what the specific reason is.

If you write a standard DLL. It can be in the initialization function DllMain.It will perform a lot of loading of the ear thread and exit of the multi-thread. There are a lot of other problems with initializing the VB6 runtime and then uninstalling it.

https://www.vbforums.com/showthread....DLL&highlight=

Like secure subclassing in VB6 idE, perhaps the easiest way to do this is to write an addin plugin. Such as pausing a program or closing a running project, add your own menus and buttons to execute.
Before you need to exit a thread or shut down a program, let it handle tasks such as reclaiming memory. Because windows tasks are asynchronous, it is always incorrect to close them directly.

You can try multithreading running alone in the VB6 IDE. Release it as another code bank module.

It is also a better way to execute some simple weak star cities in idE without crashing.
There are always some conflicts and other problems between single thread and multi-thread running purely in a process, so it is safer and more reliable to run many times safely in IDE.
If your assembly level and debugging ability are very good, you should be able to solve the multi-threaded crash problem in the VB6 IDE.

Code:

---

Option Explicit

Private Type uuid
    data1      As Long
    data2      As Integer
    data3      As Integer
    data4(7)    As Byte
End Type

Public hInstance    As Long

Private lpInst_    As Long
Private lpUnk_      As Long
Private lpVBHdr_    As Long

' ????? ?????
Public Function DllMain(ByVal hInstDll As Long, ByVal fdwReason As Long, ByVal lpvReserved As Long) As Long
    Dim lpProc      As Long
    Dim lpInst      As Long
    Dim lpUnk      As Long
    Dim lpVBHdr    As Long
   
    ' ??? ???????? ???????? ?????????????? ?????? ?????? ??????????
    If fdwReason = DLL_PROCESS_ATTACH Then
        ' ???????? ?????? ??? ??????, VBHeader, ? ??? ????????? ??????????? ??? ?????????????
        lpProc = GetProcAddress(hInstDll, "DllGetClassObject")
        If lpProc = 0 Then Exit Function
        GetMem4 ByVal lpProc + 2, lpVBHdr
        GetMem4 ByVal lpProc + 7, lpUnk
        GetMem4 ByVal lpProc + 12, lpInst
        DllMain = InitRuntime(lpInst, lpUnk, lpVBHdr, hInstDll, fdwReason, lpvReserved)
        lpInst_ = lpInst: lpUnk_ = lpUnk: lpVBHdr_ = lpVBHdr: hInstance = hInstDll
    ElseIf fdwReason = DLL_THREAD_ATTACH Then
        DllMain = InitRuntime(lpInst_, lpUnk_, lpVBHdr_, hInstDll, fdwReason, lpvReserved)
    Else
        vbCoUninitialize
        DllMain = UserDllMain(lpInst_, lpUnk_, hInstDll, fdwReason, ByVal lpvReserved)
    End If
   
End Function

Private Function InitRuntime(ByVal lpInst As Long, ByVal lpUnk As Long, ByVal lpVBHdr As Long, ByVal hInstDll As Long, _
                            ByVal fdwReason As Long, ByVal lpvReserved As Long) As Long
    Dim iid    As uuid
    Dim clsid  As uuid
   
    InitRuntime = UserDllMain(lpInst, lpUnk, hInstDll, fdwReason, ByVal lpvReserved)
    If InitRuntime Then
        vbCoInitialize ByVal 0&
        iid.data4(0) = &HC0: iid.data4(7) = &H46                    ' IUnknown
        VBDllGetClassObject lpInst, lpUnk, lpVBHdr, clsid, iid, 0  ' ????????????? ??????
    End If
End Function

---

The best use of IOCP is for.websocket,mqtt,sse,webserver()like iis,- Apache HTTP Serve,nginx

It can even be used for stock trading. Operate automated transactions in Bitcoin. Even mining.

Of course, the use of us ordinary people can be used to initiate some post requests.

For example, some people in the forum often operate rc6 and put 30 to 50 transparent PNG pictures. Overlay, and then control the replacement or display and hiding of a layer respectively.
If this is the only usage, using WebBrowser is the easiest way.
But it needs to load 30 PNG files at the same time.
How to create a simple TCP server in a program? The web server sends PNG images directly from resource files or dynamically.

Or merge 30 images into one PNG file. The original height may be 700 pixels, but now it may become 20,000 pixels.
Then use JS code to parse it into 30 PNG objects from the web page.

Quote:

---

Originally Posted by xiaoyao

I've tried it many times, and sometimes I can run it several times in a row without crashing, and sometimes it crashes again.
I don't know what the specific reason is.

---

I have recently been working on a remote picture viewer, and this particular program has run all day as a picture server without a failure. The only failure was when I attempted to shut it down. Having said that, it has not undergone adequate testing with multiple connections, as I simply do not have the resources.

J.A. Coutts

Now in VB6 IDE, multiple F5 runs can be turned off and started without crashing, making it a relatively stable example of multithreading

Code:

---

Dim StopOk As Boolean
Private Sub cmdInit_Click()
    cmdInit.Enabled = False
    NumThreads = Environ("NUMBER_OF_PROCESSORS")
    Print "Number of processors is " & NumThreads
    Call ThreadInit(NumThreads)
    cmdInit.Visible = False
    lblStatus.Caption = "RUNNING!"
End Sub


Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer)
If Not StopOk Then
    Me.Visible = False
    StopOk = True
    Cancel = 1
  Call ThreadTerminate(NumThreads)
    Releasesocket
    Timer1.Enabled = True
End If
End Sub

Private Sub Timer1_Timer()
Timer1.Enabled = False
Unload Me
End Sub

---

your demo how to use?send file or GET DOWNLOAD file?

Quote:

---

Originally Posted by xiaoyao

your demo how to use?send file or GET DOWNLOAD file?

---

Have you tried the supplied GetFile program? It uses SimpleSck, which is older and slower, but it should still work.

I am close to having the remote picture viewer ready for posting. It crashes when downloading an 11 MB file, but works fine with a 1.6 MB file.

J.A. Coutts

Quote:

---

Originally Posted by couttsj

Have you tried the supplied GetFile program? It uses SimpleSck, which is older and slower, but it should still work.

I am close to having the remote picture viewer ready for posting. It crashes when downloading an 11 MB file, but works fine with a 1.6 MB file.

J.A. Coutts

---

you need upload a full project for test.use project group
one is server,one is client,only for click send file

but your project i try about 3 hours,can't run it together

As long as the design is good, 100MB or 1000MB can be sent completely

Quote:

---

Originally Posted by xiaoyao

you need upload a full project for test.use project group
one is server,one is client,only for click send file

but your project i try about 3 hours,can't run it together

As long as the design is good, 100MB or 1000MB can be sent completely

---

I presume you have defined the SharePath in the server. The default is C:\share\ and it is located in ModMT.

J.A. Coutts

Quote:

---

Originally Posted by couttsj

I presume you have defined the SharePath in the server. The default is C:\share\ and it is located in ModMT.

J.A. Coutts

---

You need to design a code that works out of the box
For example, the client can click to send and the server can receive.

Maybe I'm wrong. This is a function similar to FTP download.
There are many files on the server and clients. Send the command and then get the data from it.

The main reason is that your example is not complete.

The IOCP_Svr program has been substantially modified. The main change has been to move the work function from a class to a module and to put the Listen function on its own thread. This has allowed for all the delays to be removed. Printing functions used by VB6 (eg. Debug.Print) sometimes interferes with API functions used. Therefore, debugging information can be displayed in a text box using DbgPrint. This function uses TryEnterCriticalSection to isolate it from conflicting threads.

I used "C:\share" to list files to share on the server, and on the receiving end I used "C:\Download" to store the files downloaded. Headers are used on all records, with the initial client connection sending "Hello". The server responds with a list of the shared file names and size separated by a space. The Client saves the file names to a list box. When the client selects a file to download, it opens a file with the file length provided. If that file already exists, it asks the client if it is to be overwritten. It then sends the file name to the server and the server responds.

There is an outstanding problem that I have not been able to resolve, and any assistance would be appreciated. When I attempt to exit the program after several large file downloads, the IDE itself shuts down.
----------------------------------------------------
1,646,411 EndCliff.JPG - Using single connection
EndCliff.JPG Saved in 375ms
EndCliff.JPG Saved in 265ms
EndCliff.JPG Saved in 296ms
EndCliff.JPG Saved in 344ms
(IDE remained when program exited)
1,646,411 EndCliff.JPG - Using multiple connections
EndCliff.JPG Saved in 375ms
EndCliff.JPG Saved in 407ms
EndCliff.JPG Saved in 375ms
EndCliff.JPG Saved in 360ms
(IDE remained when program exited)

11,533,852 sample.jpg - Using single connection
sample.jpg Saved in 2750ms
sample.jpg Saved in 2453ms
sample.jpg Saved in 2687ms
sample.jpg Saved in 2313ms
(IDE shut down when program exited)
11,533,852 sample.jpg - Using multiple connections
sample.jpg Saved in 4984ms
sample.jpg Saved in 4938ms
sample.jpg Saved in 5297ms
sample.jpg Saved in 5250ms
(IDE shut down when program exited)
---------------------------------------------------
It looks like something is not being properly cleaned up after sending larger files, but I have no idea what that is.

J.A. Coutts
Note: All testing so far has been between the client on a WiFi network and a server on a wired network.

As I developed IOCP_Svr in the IDE, I neglected to test the executable. When I finally did, the executable would display the form and then disappear. The program was based on an Echo Server called "#Prj_VB_iocp_Server_En1.vbp". An Echo Server did not come close to meeting my requirements, but it was a good starting point. So I went back to the original and started all over, this time testing the executable as I went along.

It turned out that there were several issues, that all seemed to be related to string manipulation within the worker routine. I have no idea why.
1. Each received record was copied, cleared, and the header recovered and removed. That was changed to shifting the buffer left 5 places after recovering the header.
2. The executable did not like the file list creation routine, so it was moved outside of the worker routine and stream lined.
3. The file name was originally saved in a string array. That was changed to a simple string.
4. To access files, the API required pointers only. The code originally used "lstrcpyW" and "lstrlenW" to create the file name from the pointer. This was changed by transferring the string name as well and using "StrPtr" to open the file.

There was one small change required to the Client program, so that download has also been updated.

I am not going to suggest that this is the last of my problems with this program, but it appears to have addressed the crashing of the executable.

J.A. Coutts

I think if you are just looking for a high-performance socket server, this library might be of help to you.

cWinsock Class Development Documentation | VB6 PRO DOCS
https://doc.vb6.pro/en/vbman/winsock/overview.html

vbman 's cWisncok is based on VbAsyncSocket: [email protected], but encapsulates a simpler and more user-friendly object that you can keep Winsock.ocx as it is, but it is better. Similarly, vbman is free and will be open-sourced after the migration to Twinbasic

Quote:

---

Originally Posted by woeoio

I think if you are just looking for a high-performance socket server, this library might be of help to you.

cWinsock Class Development Documentation | VB6 PRO DOCS
https://doc.vb6.pro/en/vbman/winsock/overview.html

---

Thank you for the feedback. Microsoft is clear that the highest throughput is achieved using Overlapped I/O in non-blocking or asynchronous mode using multiple threads. I only supplied the Client program because it was needed in order to interface with the server, and SimpleSock for me was stable and manageable. Any Client program could have been used, and Vbman may indeed be better suited, but this post is essentially about the high speed server.

J.A. Coutts

Quote:

---

Originally Posted by couttsj

Thank you for the feedback. Microsoft is clear that the highest throughput is achieved using Overlapped I/O in non-blocking or asynchronous mode using multiple threads. I only supplied the Client program because it was needed in order to interface with the server, and SimpleSock for me was stable and manageable. Any Client program could have been used, and Vbman may indeed be better suited, but this post is essentially about the high speed server.

J.A. Coutts

---

Yes, I'm sorry, it's my fault that I didn't see the previous context

Please note that if you are going to transfer fairly large files using the executable, you will need to adjust the buffer size (MAX_PERBUFLEN). The current posting of IOCP_Svr uses a buffer size of 1,024 and crashes when transferring an 11MB file, but not when using a 8,192 byte buffer.

J.A. Coutts