kill off remaining kgio uses

kgio is an extra download and shared object which costs users
bandwidth, disk space, startup time and memory.  Ruby 2.3+
provides `Socket#accept_nonblock(exception: false)' support
in addition to `exception: false' support in IO#*_nonblock
methods from Ruby 2.1.

We no longer distinguish between TCPServer and UNIXServer as
separate classes internally; instead favoring the `Socket' class
of Ruby for both.  This allows us to use `Socket#accept_nonblock'
and get a populated `Addrinfo' object off accept4(2)/accept(2)
without resorting to a getpeername(2) syscall (kgio avoided
getpeername(2) in the same way).

The downside is there's more Ruby-level argument passing and
stack usage on our end with HttpRequest#read_headers (formerly
HttpRequest#read).  I chose this tradeoff since advancements in
Ruby itself can theoretically mitigate the cost of argument
passing, while syscalls are a high fixed cost given modern CPU
vulnerability mitigations.

Note: no benchmarks have been run since I don't have a suitable
system.

1 files changed, 0 insertions, 1 deletions

diff --git a/unicorn.gemspec b/unicorn.gemspec
index 7bb1154..85183d9 100644
--- a/unicorn.gemspec
+++ b/unicorn.gemspec
@@ -36,7 +36,6 @@ Gem::Specification.new do |s|
   # won't have descriptive text, only the numeric status.
   s.add_development_dependency(%q<rack>)
 
-  s.add_dependency(%q<kgio>, '~> 2.6')
   s.add_dependency(%q<raindrops>, '~> 0.7')
 
   s.add_development_dependency('test-unit', '~> 3.0')