ID Number: Q83808
3.00
WINDOWS
Summary:
Windows supports multiple references to a given resource. For example,
suppose that an application has two top-level menus that each contain
the same submenu. (An application can use the AppendMenu or SetMenu
functions to add a submenu to another menu at run time.)
Normally, destroying a menu destroys all of its submenus. In the case
above, however, when one menu is destroyed, the other menu has a lock
on the common submenu. Therefore, the common submenu remains in memory
and is not destroyed. The handle to the submenu remains valid until
all references to the submenu are removed. The submenu either remains
in memory or is discarded, while its handle remains valid.
More Information:
Windows maintains a lock count for each resource, including menus.
When the lock count falls to zero, Windows can free (destroy) the
object. Each time an application loads a resource, its lock count is
incremented. If a resource is loaded more than once, only one copy is
created; subsequent loads only increment the lock count. Each call to
free a resource decrements its lock count.
When the LoadResource function determines if a resource has already
been loaded, it also determines if the resource has been discarded. If
so, LoadResource loads the resource again. The resource is not
necessarily present in memory at all times. However, if the lock count
is not zero and the resource is discarded, Windows will automatically
reload the resource. All resources are discardable and will be
discarded if required to free memory.
Therefore, in the example above, the application's call to the
DestroyMenu function calls FreeResource, which checks the lock count.
This process is analogous to LoadMenu, which calls LoadResource.
Additional reference words: 3.00