Q153904: How To Perform Background Processing in FoxPro
Article: Q153904
Product(s): Microsoft FoxPro
Version(s): 3.00 3.00b
Operating System(s):
Keyword(s): kbvfp300 kbvfp300b kbvfp600
Last Modified: 04-AUG-1999
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The information in this article applies to:
- Microsoft Visual FoxPro for Windows, versions 3.0, 3.0b, 6.0
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SUMMARY
=======
This article describes how to create a process to run another program in a
background of FoxPro using API routines and how to use some API calls related to
a process. The tasks described in this article are available as commands in
Microsoft FoxPro versions 3.0 and 3.0b.
NOTE: The following sample uses native Win32 applications.
MORE INFORMATION
================
A Windows-based application that performs a long background task, such as
scanning serial ports, can be designed using Win32 API calls.
In FoxPro, the procedure code could be called in a timer method to facilitate
checking for characters at semi-regular intervals. However, if large amounts of
data are expected to be received from the serial port, this technique will
reduce the chance of over-running the input buffer. This article discusses the
code required to implement such a task in a separate module that can be executed
in a background.
The CreateProcess function is used to run a new program by creating a process. In
addition to creating a process, CreateProcess also creates a thread object (a
primary thread).
The RUN command in FoxPro can be used to run a specified external MS-DOS program
in a window. While the MS-DOS program or command is running, the title of the
window is FoxPro Run Command. In FoxPro for Windows, after the external program
or command is finished executing, the window title changes to Inactive FoxPro
Run Command. The FoxPro for Windows menu system is disabled until this window is
closed. In Visual FoxPro, the FoxPro Run Command window is closed after the
external program or command is finished executing. In other words, FoxPro
application does not have the control until the external program is finished
executing.
By using API calls, it is possible to run the specified external windows
application in a background while the users have full control over their own
FoxPro application.
In this article, the customized API routine was written using Microsoft Visual
C++ 4.0 to create a process and a thread.
The following sample program illustrates the contents of the .DLL file written in
Microsoft Visual C++ 4.0. It shows a way to create a process through the Win32
SDK.
NOTE: This sample program illustrates many Microsoft Visual C++ commands. The use
of these commands is beyond the scope of Microsoft FoxPro Product Support. Users
with substantial experience using API routines should be able to write the
following sample .DLL file. For this sample .DLL file to work, you need a .DEF
file to export the disable function.
Sample Program (DLL - to initiate a background program)
-------------------------------------------------------
#include <windows.h>
#include <stdio.h>
HANDLE hInst;
HWND hDlg;
HANDLE hHeap;
BOOL APIENTRY DllMain(HANDLE hInst, DWORD ul_reason_being_called, LPVOID
lpReserved)
{
return 1;
UNREFERENCED_PARAMETER(hInst);
UNREFERENCED_PARAMETER(ul_reason_being_called);
UNREFERENCED_PARAMETER(lpReserved);
}
double APIENTRY backgrnd(void)
{
PROCESS_INFORMATION pInfo;
STARTUPINFO sInfo;
DWORD exitCode;
sInfo.cb = sizeof(STARTUPINFO);
sInfo.lpReserved = NULL;
sInfo.lpReserved2 = NULL;
sInfo.cbReserved2 = 0;
sInfo.lpDesktop = NULL;
sInfo.lpTitle = NULL;
sInfo.dwFlags = 0;
sInfo.dwX = 0;
sInfo.dwY = 0;
sInfo.dwFillAttribute = 0;
sInfo.wShowWindow = SW_SHOW;
// The path to notepad.exe in this example is for
// Windows NT. Your path may be different.
if (!CreateProcess("c:\\winnt351\\system32\\notepad.exe",
NULL,
NULL,
NULL,
FALSE,
0,
NULL,
NULL,
&sInfo,
&pInfo)) {
printf("ERROR: Cannot launch child process\n");
exit(1);
}
// Give the process time to execute and finish
WaitForSingleObject(pInfo.hProcess, 50L);
return pInfo.dwProcessId;
}
Sample Program (DLL - to terminate the background program)
----------------------------------------------------------
#include <windows.h>
#include <stdio.h>
HANDLE hInst;
HWND hDlg;
HANDLE hHeap;
BOOL APIENTRY DllMain(HANDLE hInst, DWORD ul_reason_being_called, LPVOID
lpReserved)
{
return 1;
UNREFERENCED_PARAMETER(hInst);
UNREFERENCED_PARAMETER(ul_reason_being_called);
UNREFERENCED_PARAMETER(lpReserved);
}
void APIENTRY terminat(double processid)
{
//PROCESS_INFORMATION pInfo;
DWORD exitCode;
HANDLE fhandle;
fhandle = OpenProcess(PROCESS_ALL_ACCESS, TRUE, (DWORD)processid);
if (GetExitCodeProcess(fhandle, &exitCode))
{
switch(exitCode)
{
case STILL_ACTIVE: printf("Process is still active\n");
break;
default: printf("Exit code = %d\n", exitCode);
break;
}
}
else {
printf("GetExitCodeProcess() failed\n");
}
BOOL TermSucc;
TermSucc= TerminateProcess(fhandle, exitCode);
if (TermSucc == FALSE)
printf("TerminateProcess");
else
printf("Process terminated successfully!\n");
}
Sample Program (FoxPro)
-----------------------
PUBLIC DOUBLE phandle
phandle = 0
DECLARE DOUBLE backgrnd IN c:\BACKGRND.DLL
phandle = backgrnd()
WAIT WINDOW("Note Pad is now Running")
DECLARE terminat IN c:\TERMINAT.DLL DOUBLE
FoxHWND = terminat(phandle)
Sample Program (Notes)
----------------------
- To create a .DLL file in Visual C++, please refer to a Help file in Microsoft
Visual C++ 4.0.
- Make a note that the Backgrnd.dll and Terminat.dll should be in the same
directory as your project, or should be in the path of the Windows Win32
directory.
The API function Backgrnd returns a process id. This process id should be used as
a parameter to call terminate API function which will terminate the process
based on the given id.
Furthermore, the backgrnd.dll creates the process in the separate address space
with an unique process id and handle. After the process is created, you have
access to your FoxPro program (your FoxPro and the C program (DLL) will run
simultaneously). Once the process is created with the primary thread, the C
program will run separately from the FoxPro application until you specifically
ask it to terminate. A good way to terminate the process is when the user quits
the FoxPro program.
You should implement the terminat.dll code inside the last event of your project
such as a Destroy event.
This sample code is designed to work with only one process and will only work
under Windows NT or Windows 95.
Additional query words: VFoxWin
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Keywords : kbvfp300 kbvfp300b kbvfp600
Technology : kbVFPsearch kbAudDeveloper kbVFP300 kbVFP300b kbVFP600
Version : 3.00 3.00b
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