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Asked: 2026-05-11T05:41:23+00:00

I’ve already looked at this question , and I’ve already checked out the suggestions

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I’ve already looked at this question, and I’ve already checked out the suggestions that were made there. My program creates and destroys a lot of UI controls (a lot of UI controls), and anything that makes controls hang around after they’re ‘destroyed’ will cause this problem. (Fun fact: if you don’t set a ToolStrip control’s Visible property to false before you destroy its container, it doesn’t get disposed, because it’s still registered with Windows to receive theme-change events; it only unregisters itself when it’s not visible, and it apparently doesn’t have any way of knowing that this is happening when its container is being destroyed.)

The thing is, it’s actually possible that my application really is running out of window handles. The program’s got a single form that has nested tab controls. Each parent tab has 12 or 13 child tabs, and a child tab can have 30 or 40 controls on it. It’s quite possible for the user to have 15 parent tabs open at any given time, and that’s getting into the territory of 5000+ live controls in the application. And I know that many of my controls use more than one window handle.

(And before you say ‘well, it looks like you’ve designed the UI wrong,’ let me disabuse of that: the whole reason the application exists in the first place is that the users have an enormous space of data that they need to be able to navigate to quickly. The tabs-within-tabs thing actually works really well for them.)

My understanding is that there’s a hard limit of 10,000 window handles per application. If that’s actually true (I understand a lot of things to be true that aren’t), then I’m going to have to manage my app’s use of them. I can, for instance, throw away the contents of the least recently used tab when I start running low on window handles.

But how do I tell that I’ve started running low on window handles? And is this really the right approach to the problem?

(This is but one of the many reasons that I’d like to rebuild this UI in WPF.)

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1 Answer

  1. I’ve fixed this problem, which I’ve described in detail in this answer. I answered it there instead of here mostly because I got mad(der) at Raymond Chen when I read the other responses to the question.

    The short answer:

    1. Maintain an LRU cache of tab pages that gets updated whenever the user visits one.
    2. Count the window handles in use before creating a new tab page.
    3. If too many window handles are in use, dispose the contents of least-recently-visited tab pages until the number of window handles in use gets down to a safe level.
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