Based on hamishm's original patch from 2015, but heavily modified,
refactored, and reworked.
From the original commit message:
> When an object is deleted, a B_EVENT_INVALID event is delivered,
> and the object is unregistered from the queue.
>
> The special event flag B_EVENT_ONE_SHOT can be passed in when adding
> an object so that the object is automatically unregistered when an
> event is delivered.
Modifications to the original change include:
* Removed the public interface (syscalls remain private for the moment)
* Event list queueing/dequeueing almost entirely rewritten, including:
- Clear events field when dequeueing.
- Have B_EVENT_QUEUED actually indicate whether the event has been
appended to the linked list (or not), based around lock state.
The previous logic was prone to races and double-insertions.
- "Modify" is now just "Deselect + Select" performed at once;
previously it could cause use-after-frees.
- Unlock for deselect only once at the end of dequeue.
- Handle INVALID events still in the queue upon destruction,
fixing memory leaks.
* Deduplified code with wait_for_objects.
* Use of C++ virtual dispatch instead of C-style enum + function calls,
and BReferenceable plus destructors for teardown.
* Removed select/modify/delete flags. Select/Modify are now the same
operation on the syscall interface, and "Delete" is done when 0
is passed for "events". Additionally, the events selected can be fetched
by passing -1 for "events".
* Implemented level-triggered mode.
* Use of BStackOrHeapArray and other convenience routines in syscalls.
Change-Id: I1d2f094fd981c95215a59adbc087523c7bbbe40b
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6745
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>
