NSOperationQueue maxConcurrentOperationCount –1 and undocumented system throttling boundary

NSOperationQueue is configured with maxConcurrentOperationCount set to –1, which is documented as unlimited. In practice the system caps the number of concurrent threads for a queue based on CPU and memory resources.

The throttling policy and thresholds are not documented, and the queue’s internal throttling state is not exposed through a public API. Developers therefore have no permission boundary to query effective concurrency or adjust system-level limits, leaving the behavior opaque across iOS and macOS.

The goal is to establish a deterministic configuration boundary for queues used under high concurrent load where latency must remain predictable.

Is there a documented API to observe the effective concurrency applied by the system for a queue with maxConcurrentOperationCount –1? Does Apple intend the –1 setting to be a performance contract or an advisory hint subject to opaque throttling? What configuration is required to avoid non-deterministic latency spikes under concurrent requests?