Improved java extension loading.

The original implementation assumed that the Java extensions would
always be compiled and loaded when running on JRuby. This is not always
the case. During development and testing if the gem in included directly
from source, as when the Gemfile references git directly, none of the
native extensions will exist. In production if the pure-Ruby gem
is loaded under JRuby the extensions won't exist, either.

This commit updates Java extension loading to follow the existing
pattern for C extensions. Relevant parts of the code check to see if the
extensions have been correctly loaded first, rather than assuming they
are. The test suite still assumes that Java and C extensions are loaded,
however. This is necessary to catch bugs which prevent extensions from
properly compiling and loading.

Author: jdantonio

lib/concurrent/atomic/atomic_boolean.rb

@@ -48,7 +48,7 @@ module Concurrent
   #   Explicitly sets the value to false.
   #
   #   @return [Boolean] true is value has changed, otherwise false
-  
+
   ###################################################################
 
   # @!macro [new] atomic_boolean_public_api
@@ -79,7 +79,7 @@ module Concurrent
   # @!visibility private
   # @!macro internal_implementation_note
   AtomicBooleanImplementation = case
-                                when Concurrent.on_jruby?
+                                when defined?(JavaAtomicBoolean)
                                   JavaAtomicBoolean
                                 when defined?(CAtomicBoolean)
                                   CAtomicBoolean

lib/concurrent/atomic/atomic_fixnum.rb

@@ -96,7 +96,7 @@ module Concurrent
   # @!visibility private
   # @!macro internal_implementation_note
   AtomicFixnumImplementation = case
-                               when Concurrent.on_jruby?
+                               when defined?(JavaAtomicFixnum)
                                  JavaAtomicFixnum
                                when defined?(CAtomicFixnum)
                                  CAtomicFixnum

lib/concurrent/atomic/semaphore.rb

@@ -91,7 +91,7 @@ module Concurrent
   # @!visibility private
   # @!macro internal_implementation_note
   SemaphoreImplementation = case
-                            when Concurrent.on_jruby?
+                            when defined?(JavaSemaphore)
                               JavaSemaphore
                             else
                               MutexSemaphore

lib/concurrent/map.rb

@@ -1,30 +1,31 @@
 require 'thread'
 require 'concurrent/constants'
+require 'concurrent/utility/native_extension_loader'
 
 module Concurrent
   # @!visibility private
   module Collection
 
     # @!visibility private
-    MapImplementation = if defined?(RUBY_ENGINE)
-                   case RUBY_ENGINE
-                   when 'jruby'
-                     # noinspection RubyResolve
-                     JRubyMapBackend
-                   when 'ruby'
-                     require 'concurrent/collection/map/mri_map_backend'
-                     MriMapBackend
-                   when 'rbx'
-                     require 'concurrent/collection/map/atomic_reference_map_backend'
-                     AtomicReferenceMapBackend
-                   else
-                     warn 'Concurrent::Map: unsupported Ruby engine, using a fully synchronized Concurrent::Map implementation' if $VERBOSE
-                     require 'concurrent/collection/map/synchronized_map_backend'
-                     SynchronizedMapBackend
-                   end
-                 else
-                   MriMapBackend
-                 end
+    MapImplementation = if Concurrent.java_extensions_loaded?
+                          # noinspection RubyResolve
+                          JRubyMapBackend
+                        elsif defined?(RUBY_ENGINE)
+                          case RUBY_ENGINE
+                          when 'ruby'
+                            require 'concurrent/collection/map/mri_map_backend'
+                            MriMapBackend
+                          when 'rbx'
+                            require 'concurrent/collection/map/atomic_reference_map_backend'
+                            AtomicReferenceMapBackend
+                          else
+                            warn 'Concurrent::Map: unsupported Ruby engine, using a fully synchronized Concurrent::Map implementation' if $VERBOSE
+                            require 'concurrent/collection/map/synchronized_map_backend'
+                            SynchronizedMapBackend
+                          end
+                        else
+                          MriMapBackend
+                        end
   end
 
   # `Concurrent::Map` is a hash-like object and should have much better performance

lib/concurrent/synchronization/jruby_lockable_object.rb

@@ -1,7 +1,7 @@
 module Concurrent
   module Synchronization
 
-    if Concurrent.on_jruby?
+    if Concurrent.on_jruby? && Concurrent.java_extensions_loaded?
 
       # @!visibility private
       # @!macro internal_implementation_note

lib/concurrent/synchronization/jruby_object.rb

@@ -1,7 +1,7 @@
 module Concurrent
   module Synchronization
 
-    if Concurrent.on_jruby?
+    if Concurrent.on_jruby? && Concurrent.java_extensions_loaded?
 
       # @!visibility private
       # @!macro internal_implementation_note

lib/concurrent/synchronization/lockable_object.rb

@@ -8,7 +8,7 @@ module Synchronization
                                      MriMonitorLockableObject
                                    when Concurrent.on_cruby? && Concurrent.ruby_version(:>, 1, 9, 3)
                                      MriMutexLockableObject
-                                   when Concurrent.on_jruby?
+                                   when defined? JRubyLockableObject
                                      JRubyLockableObject
                                    when Concurrent.on_rbx?
                                      RbxLockableObject

lib/concurrent/synchronization/object.rb

@@ -6,7 +6,7 @@ module Synchronization
     ObjectImplementation = case
                            when Concurrent.on_cruby?
                              MriObject
-                           when Concurrent.on_jruby?
+                           when defined? JRubyObject
                              JRubyObject
                            when Concurrent.on_rbx?
                              RbxObject

lib/concurrent/utility/native_extension_loader.rb

@@ -7,42 +7,57 @@ module Utility
     # @!visibility private
     module NativeExtensionLoader
 
-      @c_ext_loaded    ||= false
-      @java_ext_loaded ||= false
-
-      # @!visibility private
       def allow_c_extensions?
         Concurrent.on_cruby?
       end
 
-      if Concurrent.on_cruby? && !@c_ext_loaded
-        tries = [
-          lambda do
-            require 'concurrent/extension'
-            @c_ext_loaded = true
-          end,
-          lambda do
-            # may be a Windows cross-compiled native gem
-            require "concurrent/#{RUBY_VERSION[0..2]}/extension"
-            @c_ext_loaded = true
-          end]
-
-        tries.each do |try|
-          begin
-            try.call
-            break
-          rescue LoadError
-            next
+      def c_extensions_loaded?
+        @c_extensions_loaded ||= false
+      end
+
+      def java_extensions_loaded?
+        @java_extensions_loaded ||= false
+      end
+
+      def set_c_extensions_loaded
+        @c_extensions_loaded = true
+      end
+
+      def set_java_extensions_loaded
+        @java_extensions_loaded = true
+      end
+
+      def load_native_extensions
+        if Concurrent.on_cruby? && !c_extensions_loaded?
+          tries = [
+            lambda do
+              require 'concurrent/extension'
+              set_c_extensions_loaded
+            end,
+            lambda do
+              # may be a Windows cross-compiled native gem
+              require "concurrent/#{RUBY_VERSION[0..2]}/extension"
+              set_c_extensions_loaded
+            end]
+
+          tries.each do |try|
+            begin
+              try.call
+              break
+            rescue LoadError
+              next
+            end
           end
         end
-      end
 
-      if Concurrent.on_jruby? && !@java_ext_loaded
-        begin
-          require 'concurrent_ruby_ext'
-          @java_ext_loaded = true
-        rescue LoadError
-          # move on with pure-Ruby implementations
+        if Concurrent.on_jruby? && !java_extensions_loaded?
+          begin
+            require 'concurrent_ruby_ext'
+            set_java_extensions_loaded
+          rescue LoadError
+            # move on with pure-Ruby implementations
+            warn 'On JRuby but Java extensions failed to load.'
+          end
         end
       end
     end
@@ -51,3 +66,5 @@ def allow_c_extensions?
   # @!visibility private
   extend Utility::NativeExtensionLoader
 end
+
+Concurrent.load_native_extensions