Blocking pool doesn't have backpressure on OSX

[vertexclique]

Longhauling blocking requests are panicking the blocking thread pool because max threads is not 10_000 for OSX. It is 4096. Current method panics.

Solution: having a variable max threads based on errors coming up from thread pool during spawning dynamic threads.

[yoshuawuyts]

This seems like it'll be resolved by #181.

[vertexclique]

No, it is not solved by that PR yet:

running 1 test
thread 'longhauling_task_join' panicked at 'cannot start a dynamic thread driving blocking tasks: Os { code: 35, kind: WouldBlock, message: "Resource temporarily unavailable" }', src/libcore/result.rs:1084:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
test longhauling_task_join ... FAILED

failures:

failures:
    longhauling_task_join

[yoshuawuyts]

@vertexclique do you have a repro perhaps?

[vertexclique]

Yes, It was fixed in the EMA branch. I wrote tests for these cases too. Reopened the branch again so you can take a look to test called longhauling_task_join. Also wrote in the PR how it can be run:
#108 (comment)
branch is here: https://github.com/vertexclique/async-std/tree/ema-based-statistically-adaptive-thread-pool