On 6/3/21 2:59 PM, André Almeida wrote:
** The wait on multiple problem
The use case lies in the Wine implementation of the Windows NT interface
WaitMultipleObjects. This Windows API function allows a thread to sleep
waiting on the first of a set of event sources (mutexes, timers, signal,
console input, etc) to signal. Considering this is a primitive
synchronization operation for Windows applications, being able to quickly
signal events on the producer side, and quickly go to sleep on the
consumer side is essential for good performance of those running over Wine.
I know this is part of the cover letter, but I really do want to clarify
that this isn't really accurate. The use case that this is referring to
is not "the Wine implementation of WaitForMultipleObjects", it is an
out-of-tree implementation of WaitForMultipleObjects that provides
improved performance compared to the in-tree implementation.
This is especially salient because:
(1) this out-of-tree implementation is only in a small handful of cases
any more performant than a different out-of-tree implementation which
uses eventfd and poll() instead;
(2) these implementations will remain out-of-tree due to compatibility
and robustness problems;
(3) I believe there is potential for an upstreamable implementation
which does not rely on futex or futex2.
