INFO: Microsoft Windows Caches Five Display Contexts (74291)
The information in this article applies to:
- Microsoft Windows Software Development Kit (SDK) 3.1
This article was previously published under Q74291
3.00 3.10
WINDOWS
kbprg
SUMMARY
The Microsoft Windows graphical environment maintains an internal
cache of five display contexts (DCs) which are shared by all
applications in the system. An application retrieves one of these DCs
when it calls the BeginPaint(), GetDC(), or GetWindowDC() functions. When an application retrieves a DC, Windows marks the DC as in use and does
not allow another application to retrieve it. When an application has
finished using a DC, it must return the DC to the cache which makes
the DC available to another application. Two APIs return a DC to
the cache: EndPaint() function (to match BeginPaint() and the ReleaseDC() function (to match GetDC() or GetWindowDC()).
If an application fails to return DCs to the DC cache correctly, the
cache becomes empty, and subsequent calls to BeginPaint(), GetDC(), and GetWindowDC() fail. Because most applications do not check to be sure
that the DC they retrieve is valid, they attempt to use an invalid DC
in a graphics device interface (GDI) call, which causes a FatalExit
error.
To avoid this problem, be sure to return DCs to the cache correctly
and check the value returned by BeginPaint(), GetDC(), and GetWindowDC() to ensure that a valid DC is available.
| Modification Type: | Minor | Last Reviewed: | 2/11/2005 |
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| Keywords: | kb16bitonly kbinfo KB74291 |
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