Filtering based on thread name.

[eliphatfs]

I'm using py-spy to profile a PyTorch program. It has a lot of threads.
I also care about the native stack traces on the main and the collation thread (--native).

The thing is py-spy can't keep up with so many threads. It shows messages like

py-spy> 1.66s behind in sampling, results may be inaccurate. Try reducing the sampling rate
py-spy> 1.81s behind in sampling, results may be inaccurate. Try reducing the sampling rate
py-spy> 2.13s behind in sampling, results may be inaccurate. Try reducing the sampling rate

I need a great bit of sampling rate (at least 40-50) for the profile to be helpful to analyze the performance, so I cannot reduce the sampling rate too much.

Thus, I want to propose a feature to be able to filter based on thread names, ignoring these queue feeder threads so py-spy only need to sample the threads that we care about. Most threads are multi-processing utility threads (QueueFeeder). It would be better if we can also control more fine-grained behaviors of the sampler, like selectively enabling --native for some threads (since the maximum sampling rate py-spy is able to keep up with dropped from ~80 to ~20 when enabling native).

[olejorgenb]

Ref: #559 (comment)