Memory Usage by MS-DOS Application Steadily Increases (195930)
The information in this article applies to:
- Microsoft Windows NT Workstation 3.51
- Microsoft Windows NT Workstation 4.0
- Microsoft Windows NT Server 3.51
- Microsoft Windows NT Server 4.0
- Microsoft Windows NT Server, Enterprise Edition 4.0
This article was previously published under Q195930 SYMPTOMS
Memory usage by any MS-DOS application that repeatedly calls the functions
_dos_findfirst or _dos_findnext may continue to grow until the application
quits. When you view the working set or private bytes using a diagnostic
tool such as Performance Monitor, the size may steadily increase over time.
CAUSE
MS-DOS applications run on Windows NT under the Windows NT Virtual DOS
Machine (NTVDM) subsystem. Each time an MS-DOS application calls the
_dos_findfirst API, memory is allocated by the NTVDM and is used to keep
the necessary search context information needed to handle subsequent calls
to _dos_findnext. This memory is not deallocated until the directory search
is complete or the process ends. The amount of memory allocated for each
_dos_findfirst request varies based on the version of Windows NT, but is in
the range of 1 KB to 2 KB for each request.
RESOLUTION
The only way the NTVDM can be sure a directory search has completed is when
either _dos_findfirst or _dos_findnext returns non-zero, which indicates no
matching entry. Applications should be written to finish each search, or
the application can be rewritten as a 32-bit application. Under Win32, the
functions FindFirstFile and FindNextFile replace the functions
_dos_findfirst and _dos_findnext respectively. The Win32 function FindClose
is provided to deallocate all related memory when the search handle is no
longer required.
| Modification Type: | Major | Last Reviewed: | 2/25/1999 |
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| Keywords: | kbprb KB195930 |
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