Remove holding Poh lock

[carllin]

Problem

Poh lock is held during expensive operations by statements of the type if let Some(_) = poh.lock().unwrap()...

Summary of Changes

Rework

Fixes #

[sakridge]

Hmm. I wouldn't expect it to be held, but good find if so..

[codecov]

Codecov Report

Merging #8838 into master will decrease coverage by <.1%.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           master   #8838     +/-   ##
========================================
- Coverage      80%     80%   -0.1%     
========================================
  Files         265     265             
  Lines       57546   57549      +3     
========================================
+ Hits        46072   46073      +1     
- Misses      11474   11476      +2

[carllin]

@sakridge hehe yeah, the lock doesn't go out of scope until the end of the block. For example, in this example: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=eb85cd168d706fb955dd40701c79c0d8, main never returns

[carllin]

@sakridge I wonder if we have this pattern anywhere else in the codebase xD, with RwLock's as well

[mvines]

Same, that's super unexpected. Maybe a compiler bug even?

[carllin]

rust-lang/rust-clippy#5219

[carllin]

https://stackoverflow.com/questions/56681822/why-does-if-let-block-the-execution-with-usage-of-mutex