tree 8c0f6f98eb867d520e95d30d32a6d0e4fe55906c
parent afbc89a263d57bb2e36ce5f07b979c739bb2e8cd
author Thomas Van Lenten <thomasvl@google.com> 1450380944 -0500
committer Thomas Van Lenten <thomasvl@google.com> 1450386350 -0500

Drop all use of OSSpinLock

Apple engineers have pointed out that OSSpinLocks are vulnerable to live locking
on iOS in cases of priority inversion:
. http://mjtsai.com/blog/2015/12/16/osspinlock-is-unsafe/
. https://lists.swift.org/pipermail/swift-dev/Week-of-Mon-20151214/000372.html

- Use a dispatch_semaphore_t within the extension registry.
- Use a dispatch_semaphore_t for protecting autocreation within messages.
- Drop the custom/internal GPBString class since we don't have really good
  numbers to judge the locking replacements and it isn't required. We can
  always bring it back with real data in the future.