WaitForSingleObject for reading serial port?

Hi

I want to read data from the serial port using api. Why don't I want to use the ms comm control? Who told you I was working in VB? :)

Right now, I'm opening the com port as a file, change the settings of it and I use ReafFile to read data from it.

The problem is, I want to read the port only when new data arrive.
If I use ReadFile, I have 3 options:
1- the function returns even if there are no data, so I need to put it in an infinite loop that takes 100% of cpu usage(not good)
2- Infinite timeout - It needs to be in a separate thread so the app will not lock. But there is no way to kill a thread doing a ReadFile, the ReadFile need to return before the thread can be killed.(not good)
3- A not infinite timeout, also in another thread but I only have to test if the thread should die before reading again. This is the best method up to date.
I'd like to read the port ONLY when new data arrive.

So, how would I read the serial port using a blocking reading, reading that I could unlock everytime I want to?

I think that the key to this answer is with ovelapping I/O, WaitFoSingleOBject and CreateEvent but I can't figure out how to use them.

Any help would be appreciated.

Thanks

Here is an example that you can, hopefully, modify to suit your needs. Hope this helps, or at least gets you started in the right direction. :)

VB Code:

'This example uses a common dialog box named CDBox
Const INFINITE = &HFFFF
Const STARTF_USESHOWWINDOW = &H1
Private Enum enSW
    SW_HIDE = 0
    SW_NORMAL = 1
    SW_MAXIMIZE = 3
    SW_MINIMIZE = 6
End Enum
Private Type PROCESS_INFORMATION
    hProcess As Long
    hThread As Long
    dwProcessId As Long
    dwThreadId As Long
End Type
Private Type STARTUPINFO
    cb As Long
    lpReserved As String
    lpDesktop As String
    lpTitle As String
    dwX As Long
    dwY As Long
    dwXSize As Long
    dwYSize As Long
    dwXCountChars As Long
    dwYCountChars As Long
    dwFillAttribute As Long
    dwFlags As Long
    wShowWindow As Integer
    cbReserved2 As Integer
    lpReserved2 As Byte
    hStdInput As Long
    hStdOutput As Long
    hStdError As Long
End Type
Private Type SECURITY_ATTRIBUTES
    nLength As Long
    lpSecurityDescriptor As Long
    bInheritHandle As Long
End Type
Private Enum enPriority_Class
    NORMAL_PRIORITY_CLASS = &H20
    IDLE_PRIORITY_CLASS = &H40
    HIGH_PRIORITY_CLASS = &H80
End Enum
Private Declare Function CreateProcess Lib "kernel32" Alias "CreateProcessA" (ByVal lpApplicationName As String, ByVal lpCommandLine As String, lpProcessAttributes As SECURITY_ATTRIBUTES, lpThreadAttributes As SECURITY_ATTRIBUTES, ByVal bInheritHandles As Long, ByVal dwCreationFlags As Long, lpEnvironment As Any, ByVal lpCurrentDriectory As String, lpStartupInfo As STARTUPINFO, lpProcessInformation As PROCESS_INFORMATION) As Long
Private Declare Function WaitForSingleObject Lib "kernel32" (ByVal hHandle As Long, ByVal dwMilliseconds As Long) As Long
Private Function SuperShell(ByVal App As String, ByVal WorkDir As String, dwMilliseconds As Long, ByVal start_size As enSW, ByVal Priority_Class As enPriority_Class) As Boolean
    Dim pclass As Long
    Dim sinfo As STARTUPINFO
    Dim pinfo As PROCESS_INFORMATION
    'Not used, but needed
    Dim sec1 As SECURITY_ATTRIBUTES
    Dim sec2 As SECURITY_ATTRIBUTES
    'Set the structure size
    sec1.nLength = Len(sec1)
    sec2.nLength = Len(sec2)
    sinfo.cb = Len(sinfo)
    'Set the flags
    sinfo.dwFlags = STARTF_USESHOWWINDOW
    'Set the window's startup position
    sinfo.wShowWindow = start_size
    'Set the priority class
    pclass = Priority_Class
    'Start the program
    If CreateProcess(vbNullString, App, sec1, sec2, False, pclass, _
    0&, WorkDir, sinfo, pinfo) Then
        'Wait
        WaitForSingleObject pinfo.hProcess, dwMilliseconds
        SuperShell = True
    Else
        SuperShell = False
    End If
End Function
Private Sub Form_Load()
    'KPD-Team 1998
    'URL: [url]http://www.allapi.net/[/url]
    'E-Mail: [email][email protected][/email]
    'Set the dialog's title
    CDBox.DialogTitle = "Choose an EXEC-File ..."
    'Error when canceled
    CDBox.CancelError = True
    'Set the dialog's filter
    CDBox.Filter = "EXEC-Files (*.exe)|*.exe|All files (*.*)|*.*"
    'Show the 'Open File'-dialog
    CDBox.ShowOpen
    'Execute the program
    SuperShell CDBox.filename, Left$(CDBox.filename, Len(CDBox.filename) - Len(CDBox.FileTitle)), 0, SW_NORMAL, HIGH_PRIORITY_CLASS
    End
End Sub