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, 3 insertions, 3 deletions

diff --git a/lib/unicorn/worker.rb b/lib/unicorn/worker.rb
index ad5814c..4af31be 100644
--- a/lib/unicorn/worker.rb
+++ b/lib/unicorn/worker.rb
@@ -71,8 +71,8 @@ class Unicorn::Worker
   end
 
   # this only runs when the Rack app.call is not running
-  # act like a listener
-  def kgio_tryaccept # :nodoc:
+  # act like Socket#accept_nonblock(exception: false)
+  def accept_nonblock(*_unused) # :nodoc:
     case buf = @to_io.read_nonblock(4, exception: false)
     when String
       # unpack the buffer and trigger the signal handler
@@ -82,7 +82,7 @@ class Unicorn::Worker
     when nil # EOF: master died, but we are at a safe place to exit
       fake_sig(:QUIT)
     when :wait_readable # keep waiting
-      return false
+      return :wait_readable
     end while true # loop, as multiple signals may be sent
   end