How to lock a file using an API function

DO decl 

#DEFINE GENERIC_READ 2147483648 && 0x80000000 
#DEFINE GENERIC_WRITE 1073741824 && 0x40000000 
#DEFINE cret  Chr(13) 
#DEFINE dcret Chr(13)+Chr(13) 

    LOCAL lcPath, lcAlias, lcFile, hFile, lnHeader, lcBuffer 
    lcPath  = GetTmpPath() 
    lcAlias = "Test" 
    lcFile  = lcPath + lcAlias + ".dbf" 

    * creating a testing table 
    IF USED (lcAlias) 
        USE IN (lcAlias) 
    ENDIF 

    IF Not FILE(lcFile) 
        SET SAFETY OFF 
        CREATE TABLE (lcFile) (dt T) 
        SET SAFETY ON 
        INSERT INTO (lcAlias) VALUES (datetime()) 
    ELSE 
        USE (lcFile) ALIAS (lcAlias) SHARED 
    ENDIF 

    lnHeader = HEADER() 
    USE IN (lcAlias) 

    lcBuffer = REPLI (Chr(0), 250) 
    hFile = OpenFile (lcFile, @lcBuffer, GENERIC_READ) 

    IF LockFile (hFile, 0,0, lnHeader,0) <> 0 
        = MessageB ("File " + lcFile + " is locked." + dcret +; 
            "At this point do not close this Dialog " +; 
            "and start another VFP instance." + dcret +; 
            "Use another instance to open " + lcFile + cret +; 
            "or just try to read the tables on " + lcPath + " " + ; 
            "using regular DIRECTORY command." + dcret +; 
            "After that click Ok to unlock the target file.", 64, "Locking a file") 

        = UnlockFile (hFile, 0,0, lnHeader,0) 
    ELSE 
        * 6 = ERROR_INVALID_HANDLE - already in exclusive use 
        ? "Error code:", GetLastError() 
    ENDIF 
    = CloseHandle (hFile) 

FUNCTION  GetTmpPath 
    LOCAL lpBuffer, lnLength 
    lpBuffer = SPACE(250) 
    lnLength = GetTempPath (LEN(lpBuffer), @lpBuffer) 
RETURN Iif (lnLength=0, "C:\Temp", PADR(lpBuffer, lnLength)) 

PROCEDURE  decl 
    DECLARE INTEGER GetLastError IN kernel32 

    DECLARE INTEGER GetTempPath IN kernel32; 
        INTEGER nBufferLength, STRING @ lpBuffer 

    DECLARE INTEGER LockFile IN kernel32; 
        INTEGER hFile, INTEGER dwFileOffsetLow,; 
        INTEGER dwFileOffsetHigh,; 
        INTEGER nNumberOfBytesToLockLow,; 
        INTEGER nNumberOfBytesToLockHigh 

    DECLARE INTEGER UnlockFile IN kernel32; 
        INTEGER hFile, INTEGER dwFileOffsetLow,; 
        INTEGER dwFileOffsetHigh,; 
        INTEGER nNumberOfBytesToUnlockLow,; 
        INTEGER nNumberOfBytesToUnlockHigh 

    DECLARE INTEGER OpenFile IN kernel32; 
        STRING   lpFileName,; 
        STRING @ lpReOpenBuff,; 
        INTEGER  wStyle 

    DECLARE INTEGER CloseHandle IN kernel32; 
        INTEGER hObject