[Backport 2.x] Fix Dispatchers.IO starvation deadlock in notification send path - #1251
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…nsearch-project#1248) * Fix Dispatchers.IO starvation deadlock in notification send path SendMessageActionHelper used runBlocking inside code already running on a Dispatchers.IO coroutine (PluginBaseAction launches every transport request on CoroutineScope(Dispatchers.IO)). The parent coroutine parked its dispatcher thread while awaiting child async(Dispatchers.IO) sends that need threads from the same pool. Under sustained concurrent sends to a slow destination (e.g. a webhook that times out), parents eventually occupy all 64 Dispatchers.IO slots. At that point no child can ever be scheduled and no parent can ever complete: a permanent dispatcher deadlock. Because all Notifications transport actions share the same scope, every plugin API (e.g. GET /_plugins/_notifications/features) hangs until the node is restarted. Replace runBlocking with structured concurrency: the send-path functions become suspend functions and use coroutineScope { ... } + awaitAll(), so waiting parents suspend and release their dispatcher threads instead of parking them. All call chains already terminate in suspend transport-action methods, so no additional bridging is needed. Reproduced by flooding 200 concurrent send requests at a webhook channel that responds after 30s: before this change the node's notifications APIs deadlock permanently (64 threads parked in runBlocking at sendMessagesInParallel, zero threads performing sends); after this change all sends complete and APIs remain responsive. Signed-off-by: Surya Sashank Nistala <snistala@amazon.com> * Add comment explaining why sendMessageToChannel is a suspend function Signed-off-by: Surya Sashank Nistala <snistala@amazon.com> --------- Signed-off-by: Surya Sashank Nistala <snistala@amazon.com> (cherry picked from commit 70804cb) Signed-off-by: opensearch-ci-bot <opensearch-infra@amazon.com>
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Backport 70804cb from #1248.