commit 449a78b1e20ea85b11f967cf3a184ee610ce21c3
author Austin Orion <auorion@microsoft.com> Tue Dec 01 18:24:50 2020
committer Commit Bot <commit-bot@chromium.org> Tue Dec 01 20:17:22 2020
tree 6c4ebd398b6982f9f18edc02317a824c869a7ea0
parent 0496a4121188a26013dca007bf6e9a7ab6d961b6

Prevent window enumeration deadlock and add unit tests.

For some time now, calls to EnumerateCapturableWindows could lead to a
deadlock if an application's main thread is waiting on the thread that
is running EnumerateCapturableWindows. This is because calls to
GetWindowText and GetWindowTextLength send a message to the window if
the window is owned by the current process. Since the main thread is
waiting on us, it will never reply to this message and we will hang.

This happens occasionally in Chromium when tearing down the
NativeDesktopMediaList object, e.g. when a user clicks "cancel" on
the capture target picker.

We can avoid this deadlock by checking if the window we are querying
is owned by the current process, and if it is then we must ensure it
is responding to messages before we call a GetWindowText* API.

This change also adds a unit test for this scenario. We create a
window and force it to be unresponsive by creating a deadlock, and
then call GetWindowList and (with the new changes) we should not
hang. Without the new changes to GetWindowListHandler, this test
would hang.

Change-Id: I2523cd735f96fd7ea60708c30cd22e5b525803f0
Bug: chromium:1152841
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/195365
Commit-Queue: Austin Orion <auorion@microsoft.com>
Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#32734}