PRB: Spawn with _P_WAIT Returns Immediately on Win32s
ID: Q125213
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The information in this article applies to:
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The C Run-Time (CRT), included with:
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Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 2.2, 4.0, 4.1
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Microsoft Win32s versions 1.30, 1.30a, 1.30c
SYMPTOMS
If you call _spawnl() with _P_WAIT from a Win32-based application, then
under Windows NT, the call returns after the spawned application has been
terminated. But under Win32s, the call returns immediately, even though the
spawned application is still running.
The return value from _spawnl() with _P_WAIT is zero if the spawned
application is a 16-bit Windows-based application or 0x103 if the
application is a Win32-based application.
CAUSE
This is due to the design of the C Run-time and a limitation of Win32s.
When the CRT does a _P_WAIT spawn, it calls CreateProcess() and checks for
failure. Next, the CRT calls WaitForSingleObject() on the process handle.
Under Windows NT, WaitForSingleObject() pauses the application until the
new process terminates, and then returns TRUE. But under Win32s,
WaitForSingleObject() returns TRUE immediately. Next, the CRT calls
GetExitCodeProcess() to find the exit status. It is a limitation that
GetExitCodeProcess() returns zero for 16-bit Windows-based application on
both Windows NT and Win32s. The return value of 0x103 for Win32-based
applications is incorrect because the application has not yet terminated.
RESOLUTION
There is no way to perform the synchronous spawn with the spawn family
of functions on Win32s. You can only perform an asynchronous spawn.
For an example of a synchronous spawn under Win32s using the Win32 API
and the Universal Thunk, please see the following article in the Microsoft
Knowledge Base:
Q125212 Performing a Synchronous Spawn Under Win32s
MORE INFORMATION
The following sample code can be used to demonstrate this behavior. The
code spawns NOTEPAD.EXE.
NOTE: The path is hard-coded, so you may have to change it if your NOTEPAD
is installed in a different directory. Under Windows NT, the message box is
displayed after NOTEPAD is closed, whereas under Win32s, the message box is
displayed before NOTEPAD is closed.
NOTEPAD is a 16-bit application under Win32s on Windows. To demonstrate the
return value of 0x103 with a Win32-based application, substitute the path
to FREECELL.EXE for the C:\\WINNT35\\SYSTEM32\\NOTEPAD.EXE in the _spawnl()
call in the code below.
Sample Code
/* Compile options needed: /MD /DWIN32 <filename>.c /link user32.lib
*/
#include <windows.h>
#include <process.h>
void main( )
{
DWORD dwVersion;
int status;
char buf[80];
dwVersion = GetVersion();
if( !(dwVersion & 0x80000000) )
{
// Windows NT: NOTEPAD must be closed before this call completes.
status = _spawnl( _P_WAIT, "c:\\winnt35\\system32\\notepad.exe",
"notepad.exe", "dummy", NULL );
}
else if( LOBYTE(LOWORD(dwVersion)) < 4 )
{
// Win32s: This call completes before NOTEPAD is closed.
status = _spawnl( _P_WAIT, "c:\\windows\\notepad.exe",
"notepad.exe", "dummy", NULL );
}
else
{
// Windows 95: for future reference.
}
wsprintf( buf, "Return Value = 0x%x\n", status );
MessageBox( NULL, buf, "Test", MB_OK );
}
Additional query words:
_spawnle _spawnlp _spawnlpe _spawnv _spawnve _spawnvp _spawnvpe win32sdk win32s
Keywords : kbCRT kbVC kbWin32s
Version : 1.0 1.3 1.3a 1.3c 2.0 2.1 2.2 4.
Platform : NT WINDOWS
Issue type : kbprb