How do I know I've hit the threads limit defined in Node?

I have limited the size of the thread pool to 25.

process.env.UV_THREADPOOL_SIZE = 25;

How can one know that all the threads are exhausted at run time?

Is there any way to find that all the define threads are exhausted during a new request?

I'm using Native Abstractions for Node.js (NAN) to call C++ functions. For every request to C++ Nan::AsyncQueueWorker is created. Here I want to find if the thread limit is exhausted and then add a safety factor.

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