Ensure the java extension is always loaded before it's needed

Author: eregon

lib/concurrent-ruby/concurrent/atomic/java_count_down_latch.rb

@@ -1,4 +1,5 @@
 if Concurrent.on_jruby?
+  require 'concurrent/utility/native_extension_loader'
 
   module Concurrent
 

lib/concurrent-ruby/concurrent/atomic/semaphore.rb

@@ -94,8 +94,8 @@ module Concurrent
 
   # @!visibility private
   # @!macro internal_implementation_note
-  SemaphoreImplementation = case
-                            when defined?(JavaSemaphore)
+  SemaphoreImplementation = if Concurrent.on_jruby?
+                              require 'concurrent/utility/native_extension_loader'
                               JavaSemaphore
                             else
                               MutexSemaphore

lib/concurrent-ruby/concurrent/exchanger.rb

@@ -289,6 +289,7 @@ def do_exchange(value, timeout)
   end
 
   if Concurrent.on_jruby?
+    require 'concurrent/utility/native_extension_loader'
 
     # @!macro internal_implementation_note
     # @!visibility private

lib/concurrent-ruby/concurrent/map.rb

@@ -10,6 +10,7 @@ module Collection
     # @!visibility private
     MapImplementation = case
                         when Concurrent.on_jruby?
+                          require 'concurrent/utility/native_extension_loader'
                           # noinspection RubyResolve
                           JRubyMapBackend
                         when Concurrent.on_cruby?

lib/concurrent-ruby/concurrent/synchronization/abstract_lockable_object.rb

@@ -1,3 +1,5 @@
+require 'concurrent/utility/native_extension_loader' # load native parts first
+
 module Concurrent
   module Synchronization