A customer found that their program was leaking GDI resources, but they couldn’t figure out why.<\/p>\n
They suspect that it may have something to do with a recent change they made. They discovered in the fine print of the documentation of the The system automatically deletes class background brushes when the class is unregistered by using Unregister\u00adClass<\/b>. An application should not delete these brushes.<\/p><\/blockquote>\n The code responsible for registering classes was registering the classes with brushes it did not own. When the original owner destroyed the brushes, that created a double-free bug. To fix the problem, they had their class registration code create a duplicate of the brush and register with the duplicate.<\/p>\n This fixed the double-free bug, but somehow it introduced a resource leak. Were they incorrect to duplicate the brush? Are all these duplicates being leaked? It seemed so, because most of the time, the program ran out of resources on the What’s going on?<\/p>\n After being reassured that the The issue was that they created a brush for the class registration, expecting the The code registers classes on demand, and before they create a window, they call hbrBackground<\/code> member of the WNDCLASS<\/code> structure<\/p>\nCreateBrushIndirect<\/code> call in their brush duplication function, which suggests that these brushes are being leaked after all.<\/p>\nRegister\u00adClass<\/code> function does indeed take ownership of the brushes used for class registrations, they went and studied their code more closely and found the problem.<\/p>\nRegister\u00adClass<\/code> to take responsibility for destroying the brush when it’s no longer needed. But they neglected to deal with the case where they register the same class more than once.<\/p>\nRegister\u00adClass<\/code> to register the class just in time. If the class is already registered, then Register\u00adClass<\/code> fails with ERROR_Register\u00adClass<\/code> does not<\/i> take responsibility for the hbrBackground<\/code> brush. In the case that Register\u00adClass<\/code> fails, the code needs to delete the brush manually.<\/p>\n