SAMPLE: TERMWAIT Spawns Task and Waits for its Termination (84456)
The information in this article applies to:
- Microsoft Windows Software Development Kit (SDK) 3.0
- Microsoft Windows Software Development Kit (SDK) 3.1
This article was previously published under Q84456 SUMMARY
Termwait.exe is a self-extracting file in the Microsoft Download Center
that demonstrates how an application can launch a child task and then wait
for it to complete before executing specific code. Termwait.exe uses
notification messages from the Toolhelp dynamic-link library (DLL) to
determine that the child task has completed. The techniques demonstrated by
the Termwait.exe sample work for both Windows and MS-DOS (non-Windows)
child tasks.
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119591 How to Obtain Microsoft Support Files from Online Services
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The Termwait.exe sample application calls the NotifyRegister() function to
install a notification callback function before it calls the WinExec()
function to launch the child task. If a callback function is
registered, it is called before any task in the system terminates. The
notification callback function calls the TaskFindHandle() function to
fill a TASKENTRY data structure with information about the terminating
task. When the callback determines that the child task has terminated,
it notifies the Termwait.exe application.
When it spawns the child task, Termwait.exe sets its bChildIsExecuting
global variable to TRUE. The notification callback resets this
variable to FALSE when the child task is complete. Any code that must
not execute while the child task is running can query the value of the
bChildIsExecuting flag. During the wait, any menu selections that
will cause reentrancy problems should be disabled. Doing so keeps the
user informed about the options that are presently valid. In the
TERMWAIT sample, the AfterChildHasTerminated() function contains code
that is executed only after the child task has completed.
If an application tracks a number of child tasks, its NotifyRegister()
callback function should process both the NFY_STARTTASK and
NFY_EXITTASK notifications. The callback function uses these
notifications to maintain a list of child task handles. Note that
while no two tasks will have the same handle, it is possible for task
handles to be reused. Consequently, if one task ends and a new task
begins, the new task can use the same task handle.
Version 3.1 of the Windows SDK is required to build the Termwait.exe
sample. However, the compiled code is compatible with both Windows 3.0
and 3.1. Note that because the TOOLHELP.DLL is not part of the default
installation for Windows 3.0, it must be installed into the Windows
system directory (by default, C:\WINDOWS\SYSTEM) before Termwait.exe will
run. The TOOLHELP.DLL file is provided as a redistributable file with
the Windows 3.1 SDK.
NOTE: The NotifyRegister callback function must be placed in a separate
source file and this file must be compiled with /GA/GEa. This is because
the NotifyRegisterCallback function is called with the Data Segment (DS) of
the task that installed the callback and the Stack egment of the task which
is notifying the callback. So SS != DS and /GA/GEs cannot be used to
compile this file.
| Modification Type: | Minor | Last Reviewed: | 8/4/2004 |
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| Keywords: | kb16bitonly kbfile kbSample KB84456 kbAudDeveloper |
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