Menu
I am thinking if there are handles of the same value ?
To clarify my question, let's say I open Notepad, type in some text, save it and then close Notepad. If I repeat this a thousand times (or even more), will I ever have a chance to see the same window handle (HWND) value being used for the Notepad main window that was used the first time? If so, why?
218
However, you can obtain the window handle by calling FindWindow() . This function retrieves a window handle based on a class name or window name. Call GetConsoleTitle() to determine the current console title. Then supply the current console title to FindWindow() .
The two main types of window handles that are fitted onto double glazed windows are, Espag handles and Cockspur handles. Then you have tilt and turn handles, spade or blade handles and monkey tail handles. Below, we'll look at these different types of window handles, how they work and why they're used.
HWND is a special HANDLE which points to a window object. HWND is said to be a pointer to a Window. To get any Window, its Child or Dialog box object, we need to use an HWND object. Communication between two windows is also done using HWND's.
Yes. There are only a finite number of values a handle can be represented by, so Windows has to reuse them eventually.
Once a handle is closed, it is gone, you can't do anything with it, it doesn't exist, and you shouldn't even look at it.
And if you subsequently open another handle, then it is possible that Windows will reuse the handle value.
68
theoretically yes. in practice - the probability of this (in contrast to process and thread id, which is frequently reused) is almost zero.
in current implementation low 16 bits of HWND used as index in windows handle table - so currently maximum 64K windows can be created. the next 16 bits used as reuse index. when a cell is used for the first time this index is 1.when this cell is reused, the index is increased by 1. and so on. as result for get the same HWND on window need how minimum 64k windows must be created and destroyed. but this is only in case all this windows will be used the same cell. but we have 64k cells. so real minimum much more higher for this. not exactly 2^32 but big enough.
and even if implementation will changed, i not think that new implementation will make HWND less unique than current.
23
By the pigeonhole principal, yes, they can't be unique.
Due to the compatibility with 32-bit processes (WoW64), handles cannot use the entire 64-bits even on 64-bit OS -- think of a 64-bit process passing a handle to a 32-bit child, or getting a handle to a window opened by a 32-bit process. This makes their true space pretty small, and thus reuse very likely.
38
Yes, window handles are reused.
Documentation to IsWindow function says:
A thread should not use
IsWindowfor a window that it did not create because the window could be destroyed after this function was called. Further, because window handles are recycled the handle could even point to a different window.
2
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
