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CompletableFuture represents a value that may complete later, with dependent stages triggered on completion. Async methods without an explicit executor commonly use a shared pool; blocking calls there can starve unrelated work. Prefer non-blocking composition, choose an executor suited to the task, set timeouts, and observe exceptional completion rather than calling join() throughout request paths.

Each platform thread consumes native resources, including stack reservation, and excessive runnable threads add scheduling and context-switching overhead. The service may hit native-thread creation errors or degrade before that point. Bound executors, measure queue depth and task latency, and apply backpressure rather than creating one thread per unbounded unit of work.

If every worker submits a task to the same bounded executor and synchronously waits for that task, no worker remains to run queued children. This is thread-pool starvation, not necessarily a monitor deadlock. Avoid blocking composition on the same pool, separate workloads, or use asynchronous completion and bounded concurrency.

Capture repeated thread dumps with jcmd or jstack while the incident is active. A deadlock cycle shows threads waiting for locks held by each other; distinguish it from starvation or a slow dependency by checking whether owners can progress. Fix consistent lock order, shorten critical sections, or redesign ownership so both locks are not required together.