[backport/v3.x] Make Sprockets::Utils.module_include thread safe on JRuby

CHANGELOG.md

@@ -1,3 +1,7 @@
+**Master**
+
+* Make `Sprockets::Utils.module_include` thread safe on JRuby. [#760](https://github.com/rails/sprockets/pull/760)
+
 **3.7.2** (June 19, 2018)
 
 * Security release for [CVE-2018-3760](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-3760).

lib/sprockets/utils.rb

@@ -147,34 +147,39 @@ def normalize_extension(extension)
       false
     end
 
+    MODULE_INCLUDE_MUTEX = Mutex.new
+    private_constant :MODULE_INCLUDE_MUTEX
+
     # Internal: Inject into target module for the duration of the block.
     #
     # mod - Module
     #
     # Returns result of block.
     def module_include(base, mod)
-      old_methods = {}
+      MODULE_INCLUDE_MUTEX.synchronize do
+        old_methods = {}
 
-      mod.instance_methods.each do |sym|
-        old_methods[sym] = base.instance_method(sym) if base.method_defined?(sym)
-      end
+        mod.instance_methods.each do |sym|
+          old_methods[sym] = base.instance_method(sym) if base.method_defined?(sym)
+        end
 
-      unless UNBOUND_METHODS_BIND_TO_ANY_OBJECT
-        base.send(:include, mod) unless base < mod
-      end
+        unless UNBOUND_METHODS_BIND_TO_ANY_OBJECT
+          base.send(:include, mod) unless base < mod
+        end
 
-      mod.instance_methods.each do |sym|
-        method = mod.instance_method(sym)
-        base.send(:define_method, sym, method)
-      end
+        mod.instance_methods.each do |sym|
+          method = mod.instance_method(sym)
+          base.send(:define_method, sym, method)
+        end
 
-      yield
-    ensure
-      mod.instance_methods.each do |sym|
-        base.send(:undef_method, sym) if base.method_defined?(sym)
-      end
-      old_methods.each do |sym, method|
-        base.send(:define_method, sym, method)
+        yield
+      ensure
+        mod.instance_methods.each do |sym|
+          base.send(:undef_method, sym) if base.method_defined?(sym)
+        end
+        old_methods.each do |sym, method|
+          base.send(:define_method, sym, method)
+        end
       end
     end