Added failure path in case of Event Enqueue fails

[Santhosha-bk]

Description

CxPlatEventQEnqueue, aka PostQueuedCompletionStatus, can fail because of OOM. The reason for this is that NtSetIoCompletion underneath PQCS must allocate an IO completion packet to add to the target IOCP *.

Same applies in case of epoll or kqueue io_uring.

Added a failure paths to finish the work inline incase of CxPlatEventQEnqueue fails.
#5369
Describe the purpose of and changes within this Pull Request.

Testing

Do any existing tests cover this change? Are new tests needed?

Documentation

Is there any documentation impact for this change?

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[mtfriesen]

I'm not sure we can simply run inline - in at least some of these files, I expect the orderly completion is relied on for serialization / mutual exclusion. Instead, we need to provide a backup mechanism that ensures orderly completion runs even if the underlying OS queue fails.

[Santhosha-bk]

@mtfriesen Rather than inline, we can try to re-add the event in queue with a delay in case of failure as a backup mechanism, we can add a 1ms delay and re-add the event like below. Please share your thoughts on this approach.

while (!CxPlatEventQEnqueue(&Worker->EventQ, &Worker->ShutdownSqe)) {
            if (++RetryCount >= MaxRetries) {
                QuicTraceLogWarning(
                    WorkerShutdownEnqueueRetry,
                    "[wrkr][%p] Shutdown enqueue failed, retry %u/%u",
                    Worker,
                    RetryCount,
                    MaxRetries);
                break;
            }
            // Exponential backoff: 1ms, 2ms, 4ms, 8ms, ...
            CxPlatSleep(1U << (RetryCount - 1));
 }

[guhetier]

I don't think that re-trying with delay is an acceptable option, and it only pushes back the problem: what happens if it keeps failing, do we hang forever? Or are we back to a fre assert?

It might also be worth checking whether the issue reported in the bug can happen for Unix.
Typically, memory management won't let an allocation failure happen (a process will either get memory or be killed).

[Santhosha-bk]

I was thinking we could have loop of 5-10 re-tries, but this is not an acceptable solution.

MsQuic stalls only in CxPlatWorkerPoolDestroyWorker because the thread waits for the worker thread to rejoin after a failed CxPlatEventQEnqueue. In all other cases where CxPlatEventQEnqueue is used, this behavior does not occur.

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