On Tue, 6 Jun 2023 16:07:53 GMT, Alexey Ivanov <[email protected]> wrote:
> **Problem description** > > If you grab the thumb of the scroll bar of `ScrollPane` and drag it slowly > and continuously up and down, you'll notice the UI stops rendering correctly: > the child component of the scroll pane will render on the left of the frame > itself, the inside of the scroll pane will be filled with the background > color of its child component. > > **Root cause** > > AWT calls the > [`::SetScrollInfo`](https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-setscrollinfo) > function on EDT when AWT processes scroll bar tracking events. This Windows > API is not thread-safe, calling this function on an incorrect thread leads to > leaking GDI objects. > > When the process reaches the limit on the number of GDI objects, it cannot > create new GDI objects, which results in rendering issues. > > **Fix** > > To resolve the problem, I modified the code so that `::SetScrollInfo` and > [`::GetScrollInfo`](https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getscrollinfo) > are always called on the toolkit thread, all AWT components are created on > the toolkit thread. > > An automatic test is provided. The test scrolls the vertical scroll bar up > and down. Then the test takes a screenshot. When the bug is reproduced, the > robot cannot create new GDI objects to capture the screenshot and it throws > `OutOfMemoryError`. The screenshot of the test case after the problem is reproduced:  If you scroll up or down, the left side of the frame gets filled with the light-green color of the canvas which is the child component inside the scroll pane. ------------- PR Comment: https://git.openjdk.org/jdk/pull/14338#issuecomment-1579061086
