Refactor characteristics read for WinRT

The characteristics read was using IAsyncOperation->put_Completed() to
process the results of descriptor reading. Each of these completed
callbacks is executed in its own thread. In our case each of the
callbacks is also calling QWinRTFunctions::await() to perform some
async operations.
As a result, if the service has a lot of characteristics, we could
end up spawning multiple threads, each of them doing some CPU-consuming
operations. Normally it's not a problem, but looks like for some
bluetooth peripherals reading the characteristics can take significant
time. Connecting to such devices can result in 100% CPU load for all
cores if the number of characteristics exceeds the number of logical
CPUs.

This patch removes the put_Completed() approach in favor of another
QWinRTFunctions::async() call. This will guarantee that all the
characteristics read operations are performed in the same worker
thread. As a drawback, characteristics reading becomes sequential,
which makes it slower.

Fixes: QTBUG-97242
Change-Id: If46c3f0afe13a56d93f2b8fc46b87a2c90555bf3
(cherry picked from commit 2a7ef291d696745887e71f8b0e27cb4c8701bdd2)
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

0 files changed, 0 insertions, 0 deletions