Expose ConnectionPool#reload

Ref: mperham/connection_pool#140

When forking a process, you need to close existing connection
to avoid sharing them across processes. `shutdown` does that, but
it also mark the pool as no longer usable.

`connection_pool` `2.2.4` introduced `#reload` that discard existing
connections, but let the pool be used again later. It's a much better
fit for an `after_fork` callback.

lib/net/http/persistent.rb

@@ -947,7 +947,8 @@ def request_setup req_or_uri # :nodoc:
   end
 
   ##
-  # Shuts down all connections
+  # Shuts down all connections. Attempting to checkout a connection after
+  # shutdown will raise an error.
   #
   # *NOTE*: Calling shutdown for can be dangerous!
   #
@@ -958,6 +959,17 @@ def shutdown
     @pool.shutdown { |http| http.finish }
   end
 
+  ##
+  # Discard all existing connections. Subsequent checkouts will create
+  # new connections as needed.
+  #
+  # If any thread is still using a connection it may cause an error!  Call
+  # #reload when you are completely done making requests!
+
+  def reload
+    @pool.reload { |http| http.finish }
+  end
+
   ##
   # Enables SSL on +connection+
 

net-http-persistent.gemspec

@@ -17,6 +17,6 @@ Gem::Specification.new do |s|
   s.required_ruby_version = ">= 2.4".freeze
   s.summary = "Manages persistent connections using Net::HTTP including a thread pool for connecting to multiple hosts".freeze
 
-  s.add_runtime_dependency(%q<connection_pool>.freeze, ["~> 2.2"])
+  s.add_runtime_dependency(%q<connection_pool>.freeze, ["~> 2.2", ">= 2.2.4"])
 end
 

test/test_net_http_persistent.rb

@@ -1244,6 +1244,17 @@ def test_shutdown
     refute c2.http.finished?, 'present generation connection must not be finished'
   end
 
+  def test_reload
+    c = connection
+
+    @http.reload
+
+    c2 = connection
+
+    assert c.http.finished?, 'last-generation connection must be finished'
+    refute c2.http.finished?, 'present generation connection must not be finished'
+  end
+
   def test_ssl
     skip 'OpenSSL is missing' unless HAVE_OPENSSL